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Beamish Stepper Motor Driver

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  • Duane C. Johnson
    Hi Wilf; I wrote to you about the defect in your XOR stepper driver. After a lot of experimenting I have come up with this version. See:
    Message 1 of 27 , Oct 28, 2002
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      Hi Wilf;

      I wrote to you about the defect in your XOR stepper
      driver. After a lot of experimenting I have come up
      with this version. See:
      http://www.redrok.com/images/beamstepper3.gif
      This version is specifically for use in solar trackers
      but may have use in beamish attraction to light.

      Features:
      1. True 4 phase stepper drive.
      ( This was the problem with the XOR design.)
      2. Essentially zero power consumption when not moving.

      Duane

      --
      Home of the $35 LED solar tracker.
      http://www.redrok.com/electron.htm#led3
      CUL8ER \ \ \ \ \ \\ \ \ Receiver
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      These are my opinions, and not that of Unisys Corp. ===
    • Duane C. Johnson
      Hi Wilf and All; I wrote to you about the defect in your XOR stepper driver. After a lot of experimenting I have come up with this version. See:
      Message 2 of 27 , Oct 29, 2002
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        Hi Wilf and All;

        I wrote to you about the defect in your XOR stepper
        driver. After a lot of experimenting I have come up
        with this version. See:
        http://www.redrok.com/images/beamstepper3.gif
        This version is specifically for use in solar trackers
        but may have use in beamish attraction to light.

        Features:
        1. True 4 phase stepper drive.
        ( This was the problem with the XOR design.)
        2. Essentially zero power consumption when not moving.

        Negatives:
        1. Requires that VCC be at twice the operating voltage
        rating of the motor

        Duane

        --
        Home of the $35 LED solar tracker.
        http://www.redrok.com/electron.htm#led3
        CUL8ER \ \ \ \ \ \\ \ \ Receiver
        Powered by\ \ \ \ \ \\ \ \ [*]
        Thermonuclear \ \Solar\Energy\from the Sun \ /////|
        Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
        \ \ \ \ \ /\ / \/ / / / |
        WA0VBE \ \ \ \ / /\ \/ / / \/ /|
        Ziggy \ \ \/ / / \ \/ \/ /\ |
        \ / \ \/ / /\ \\ / \ / / |
        "Red Rock Energy" === ===\ / \ / \ === \ / ===
        Duane C. Johnson, Designer=== === \ \ === / |
        1825 Florence St Mirrors,Heliostats,Controls & Mounts|
        White Bear Lake, Minnesota \ \ / |
        USA 55110-3364 \ \ |
        (651)635-5O65 work \ \ / |
        (651)426-4766 home use Courier New Font \ \ |
        (413)556-659O Fax copyright \ / |
        (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
        redrok@... (my primary email: address) \ |
        redrok2@... (Hotmail address) \ |
        duane.johnson@... (Unisys address) \ |
        http://www.redrok.com/index.htm (My New Web site) \|
        These are my opinions, and not that of Unisys Corp. ===
      • wilf_nv
        Very nice (beamish) Duane! Let me try my hand at a brief description of operation to see if I understand your method behind the madness. The stepper controller
        Message 3 of 27 , Oct 29, 2002
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          Very nice (beamish) Duane!

          Let me try my hand at a brief description of operation to see if I
          understand your method behind the madness.

          The stepper controller operation is as follows (I think):

          The LED photodetectors work together with Q1 and Q2 to enable either
          of the two independent oscillators. When the LEDs are aligned with
          the sun, both LED sensors would be shaded by a "shadow mask", both Q1
          and Q2 are on and both oscillators are disabled.

          When one or the other LED is illuminated, the transistor is turned
          off and the oscillator is enabled and generates a squarewave.

          The LED photodetector uses it's photovoltaic output voltage to drive
          the transistor base negative and the transistor turns off.

          Assume that LED1 is lit. LED1 anode voltage remains at +0.6V (clamped
          by the Q4 base-emitter) but the LED generates a negative voltage at
          the cathode of -1V which drives the Q1 base negative and turns off Q1
          collector current. That releases the U1E input and the oscillator
          starts.

          This is where the circuit gets funky: The outputs of the oscillators
          are connected to a "floating" RC network i.e. a network that has no
          dc connection to the supply rails. External leakage currents can
          cause the dc level in such a network to drift.
          Despite the lack of a dc reference, the average dc level of this
          network must hover near Vcc/2 for it to operate.

          Measuring waveforms in this floating network with a scope probe can
          cause problems as the probe has a 1M or 10M (x10 setting) impedance
          to GND.

          I would recommend adding a high resistance voltage divider between
          Vcc and GND with the midpoint connected to the network to stabilize
          the dc level of the network to Vcc/2 or better yet just below the
          lower trigger threshold (approximately Vcc/3)

          Keeping in mind, the necesary floating DC level of the network, the
          AC coupled waveforms, superimposed on the dc level will cross the
          thresholds of the Schmitt triggers as required.

          The U1E oscillator output is capacitively coupled via C2 through R3
          to the input of U1D. The signal will be clamped by the input
          protection network to Vcc+.6V. The output of U1D will follow the
          input without delay.
          The coupled signal from C2 also drives an integrating RC network
          formed by R4 and C2. This causes a delayed signal of Vcc/2
          superimposed on the dc to appear at the input of U1C. Since the
          normal positive switching threshold of the Schmitt trigger is 3V (
          http://www.philipslogic.com/products/hef/pdf/hef40106b.pdf ) this
          Vcc/2 signal by itself is not high enough to trigger the input of
          U1C. However with the added dc level, the signal crosses the threhold
          of U1c causing a delayed negative output pulse at the output of U1C.

          When the U1E oscillator output goes negative, the signal is couple to
          the U1D output without delay and through R4 and delay by C4 the
          signal appears at the output of U1c.

          The result is a quadrature phase relationship between the signals on
          U1D and U1C with U1C output delayed.

          Now look at the output circuit (quite weird in the best BEAM
          tradition). When the oscillators are disabled the outputs of U1c and
          U1D are both at Vcc and the capacitor C1 is charged through Q2 and Q5
          via the stepper coils to Vcc.

          Each output is buffered with a voltage follower half bridge power
          stage.

          When the outputs of U1c and U1D are pulsing, the average value of the
          voltage on C1 is Vcc/2 as the cap is alternately partially charged
          and partially discharged through the stepper coils. The result is a
          bipolar current waveform through each coil in quadrature that steps
          the motor in one direction.


          The action is the same for the case of LED2 illuminated except that
          the delayed quadrature signal will be on U1D and the motor steps in
          the reverse direction.


          Well that's it for now. Let me know how close I am.

          enjoy

          wilf


          --- In beam@y..., "Duane C. Johnson" <redrok@r...> wrote:
          > Hi Wilf and All;
          >
          > I wrote to you about the defect in your XOR stepper
          > driver. After a lot of experimenting I have come up
          > with this version. See:
          > http://www.redrok.com/images/beamstepper3.gif
          > This version is specifically for use in solar trackers
          > but may have use in beamish attraction to light.
          >
          > Features:
          > 1. True 4 phase stepper drive.
          > ( This was the problem with the XOR design.)
          > 2. Essentially zero power consumption when not moving.
          >
          > Negatives:
          > 1. Requires that VCC be at twice the operating voltage
          > rating of the motor
          >
          > Duane
          >
          > --
          > Home of the $35 LED solar tracker.
          > http://www.redrok.com/electron.htm#led3
          > CUL8ER \ \ \ \ \ \\ \ \ Receiver
          > Powered by\ \ \ \ \ \\ \ \ [*]
          > Thermonuclear \ \Solar\Energy\from the Sun \ /////|
          > Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
          > \ \ \ \ \ /\ / \/ / / / |
          > WA0VBE \ \ \ \ / /\ \/ / / \/ /|
          > Ziggy \ \ \/ / / \ \/ \/ /\ |
          > \ / \ \/ / /\ \\ / \ / / |
          > "Red Rock Energy" === ===\ / \ / \ === \ / ===
          > Duane C. Johnson, Designer=== === \ \ === / |
          > 1825 Florence St Mirrors,Heliostats,Controls & Mounts|
          > White Bear Lake, Minnesota \ \ / |
          > USA 55110-3364 \ \ |
          > (651)635-5O65 work \ \ / |
          > (651)426-4766 home use Courier New Font \ \ |
          > (413)556-659O Fax copyright \ / |
          > (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
          > redrok@r... (my primary email: address) \ |
          > redrok2@h... (Hotmail address) \ |
          > duane.johnson@u... (Unisys address) \ |
          > http://www.redrok.com/index.htm (My New Web site) \|
          > These are my opinions, and not that of Unisys Corp. ===
        • Duane C. Johnson
          Hi Wilf; ... Thanks; I must have tried a dozen variations. This works the best and is quit reliable. ... http://www.redrok.com/images/beamstepper3.gif ... Q4
          Message 4 of 27 , Oct 29, 2002
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            Hi Wilf;

            wilf_nv wrote:

            > Very nice (beamish) Duane!

            Thanks; I must have tried a dozen variations.
            This works the best and is quit reliable.

            > Let me try my hand at a brief description of operation
            > to see if I understand your method behind the madness.

            > The stepper controller operation is as follows (I think):

            http://www.redrok.com/images/beamstepper3.gif

            > The LED photodetectors work together with Q1 and Q2 to enable either
            Q4
            > of the two independent oscillators. When the LEDs are aligned with
            > the sun, both LED sensors would be shaded by a "shadow mask", both Q1
            > and Q2 are on and both oscillators are disabled.
            Q4
            > When one or the other LED is illuminated, the transistor is turned
            > off and the oscillator is enabled and generates a squarewave.

            > The LED photodetector uses it's photovoltaic output voltage to drive
            > the transistor base negative and the transistor turns off.

            > Assume that LED1 is lit. LED1 anode voltage remains at +0.6V (clamped
            > by the Q4 base-emitter) but the LED generates a negative voltage at
            > the cathode of -1V which drives the Q1 base negative and turns off Q1
            > collector current. That releases the U1E input and the oscillator
            > starts.

            > This is where the circuit gets funky: The outputs of the oscillators
            > are connected to a "floating" RC network i.e. a network that has no
            > dc connection to the supply rails. External leakage currents can
            > cause the dc level in such a network to drift.
            > Despite the lack of a dc reference, the average dc level of this
            > network must hover near Vcc/2 for it to operate.

            Actually it doesn't make much difference what the floating
            voltage is. It can be in only three regions, high, low, or
            mid. This voltage tends to stay in what ever region it
            was actively set in.

            The reason it tends to stay is due to the input current
            that flows into and out of a CMOS Schmitt trigger gate.
            I don't call this current leakage current. It's different.
            This current, although very small at less than 10uA, is
            associated with the Schmitt circuits. Depending on the
            input voltage this current changes polarity.

            Anyway, the voltage tends to stay in a range and is stable.

            > Measuring waveforms in this floating network with a scope probe can
            > cause problems as the probe has a 1M or 10M (x10 setting) impedance
            > to GND.

            Correct. I just don't do it.
            A reasonable method is to connect an emitter follower to
            a scope probe. Works pretty well for slow speed circuits
            such as these.

            > I would recommend adding a high resistance voltage divider between
            > Vcc and GND with the midpoint connected to the network to stabilize
            > the dc level of the network to Vcc/2 or better yet just below the
            > lower trigger threshold (approximately Vcc/3)

            It actually isn't needed. As the input clamps keep the voltage
            between the rails. No mater what the starting voltage it only
            takes a cycle or to to get started.

            > Keeping in mind, the necesary floating DC level of the network, the
            > AC coupled waveforms, superimposed on the dc level will cross the
            > thresholds of the Schmitt triggers as required.

            > The U1E oscillator output is capacitively coupled via C2 through R3
            > to the input of U1D. The signal will be clamped by the input
            > protection network to Vcc+.6V. The output of U1D will follow the
            > input without delay.
            > The coupled signal from C2 also drives an integrating RC network
            > formed by R4 and C2. This causes a delayed signal of Vcc/2
            > superimposed on the dc to appear at the input of U1C. Since the
            > normal positive switching threshold of the Schmitt trigger is 3V (
            > http://www.philipslogic.com/products/hef/pdf/hef40106b.pdf ) this
            > Vcc/2 signal by itself is not high enough to trigger the input of
            > U1C. However with the added dc level, the signal crosses the threhold
            > of U1c causing a delayed negative output pulse at the output of U1C.

            > When the U1E oscillator output goes negative, the signal is couple to
            > the U1D output without delay and through R4 and delay by C4 the
            > signal appears at the output of U1c.

            > The result is a quadrature phase relationship between the signals on
            > U1D and U1C with U1C output delayed.

            > Now look at the output circuit (quite weird in the best BEAM
            > tradition). When the oscillators are disabled the outputs of U1c and
            > U1D are both at Vcc and the capacitor C1 is charged through Q2 and Q5
            > via the stepper coils to Vcc.

            > Each output is buffered with a voltage follower half bridge power
            > stage.

            > When the outputs of U1c and U1D are pulsing, the average value of the
            > voltage on C1 is Vcc/2 as the cap is alternately partially charged
            > and partially discharged through the stepper coils. The result is a
            > bipolar current waveform through each coil in quadrature that steps
            > the motor in one direction.

            > The action is the same for the case of LED2 illuminated except that
            > the delayed quadrature signal will be on U1D and the motor steps in
            > the reverse direction.

            > Well that's it for now. Let me know how close I am.

            Yup, that's how I see it two.
            The circuit is a bit sensitive to capacitor tolerance in
            C2 and C4. +80 -20% capacitors should be avoided. Try to keep
            them matched matched.

            Speed is control by the oscillator capacitors and is not critical
            of values for operation, except for speed of course.

            LEDs make marvelous light sensors.
            The green ones generate up to 1.7 volts.
            In the back to back arrangement this amounts to a 3.4 volt
            change. Quite enough to drive logic gates directly.
            If set at 90 degrees to each other they have a high accuracy.
            You might think the voltage changes linearly with the
            differential illumination. This is not the case.
            Large voltage changers occur over a few degrees.

            I just posted the other variant with H-Bridge. See:
            http://www.redrok.com/images/beamstepper4.gif

            > enjoy wilf


            Duane
            > --- In beam@y..., "Duane C. Johnson" <redrok@r...> wrote:
            > > Hi Wilf and All;
            > >
            > > I wrote to you about the defect in your XOR stepper
            > > driver. After a lot of experimenting I have come up
            > > with this version. See:
            > > http://www.redrok.com/images/beamstepper3.gif
            > > This version is specifically for use in solar trackers
            > > but may have use in beamish attraction to light.
            > >
            > > Features:
            > > 1. True 4 phase stepper drive.
            > > ( This was the problem with the XOR design.)
            > > 2. Essentially zero power consumption when not moving.
            > >
            > > Negatives:
            > > 1. Requires that VCC be at twice the operating voltage
            > > rating of the motor


            --
            Home of the $35 LED solar tracker.
            http://www.redrok.com/electron.htm#led3
            CUL8ER \ \ \ \ \ \\ \ \ Receiver
            Powered by\ \ \ \ \ \\ \ \ [*]
            Thermonuclear \ \Solar\Energy\from the Sun \ /////|
            Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
            \ \ \ \ \ /\ / \/ / / / |
            WA0VBE \ \ \ \ / /\ \/ / / \/ /|
            Ziggy \ \ \/ / / \ \/ \/ /\ |
            \ / \ \/ / /\ \\ / \ / / |
            "Red Rock Energy" === ===\ / \ / \ === \ / ===
            Duane C. Johnson, Designer=== === \ \ === / |
            1825 Florence St Mirrors,Heliostats,Controls & Mounts|
            White Bear Lake, Minnesota \ \ / |
            USA 55110-3364 \ \ |
            (651)635-5O65 work \ \ / |
            (651)426-4766 home use Courier New Font \ \ |
            (413)556-659O Fax copyright \ / |
            (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
            redrok@... (my primary email: address) \ |
            redrok2@... (Hotmail address) \ |
            duane.johnson@... (Unisys address) \ |
            http://www.redrok.com/index.htm (My New Web site) \|
            These are my opinions, and not that of Unisys Corp. ===
          • Wilf Rigter
            Hi Duane, I find I appreciate the fine points of a circuit design if I try to write up a little description of operation.but no better way to test a design
            Message 5 of 27 , Oct 29, 2002
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              Hi Duane,
               
              I find I appreciate the fine points of a circuit design if I try to write up a little description of operation.but no better way to test a design than by actually building and testing it "hands on".  Anything weird or unusual popping up (hmm, that's strange) should tweak your interest (not frustration) cause it makes life interesting and often leads to brand new ideas.  You have obviously exploited every possible quirk in this novel design.
               
              I have one or two comments -
               
              You said:
               
              2. Essentially zero power consumption when not moving.
               
              and
               
              Actually it doesn't make much difference what the floating
              voltage is. It can be in only three regions, high, low, or
              mid. This voltage tends to stay in what ever region it
              was actively set in.

              With both oscillators off  (i.e. at night),  a floating dc level in the RC network can potentially maintain a stable state of one output low and the other high causing continuous current flow through both motor windings.   If the input "leakage current" level and direction is dependent on the Schmitt states, then opposite output states  would cause the floating dc level to drift to a stable Vcc/2 potential which maintains that state.  With external bias resistors setting the dc level, this posibility can be avoided.   
               
              Then you speak righteously of :
               
              LEDs make marvelous light sensors.
              The green ones generate up to 1.7 volts.
              In the back to back arrangement this amounts to a 3.4 volt
              change. Quite enough to drive logic gates directly.
              If set at 90 degrees to each other they have a high accuracy.
              You might think the voltage changes linearly with the
              differential illumination. This is not the case.
              Large voltage changers occur over a few degrees.
              Marvelous indeed!    The trick for using LED PV sensors is to keep the load capacitance very low and load resistance very high. I found that the LED photovoltaic current is in the nA range while reverse leakage photo current is in the uA range.  I am looking at 5x7 LED arrays for simple imaging applications so I am curious about the light to voltage response curve. Silicon photodiodes have a well known log response. You described large voltage changes in terms of  "a few degrees". That can be for several reasons (ie shadow edges). Any ideas why the non-linear differential  response to light levels for dual reversed LED sensors? 

              I just posted the other variant with H-Bridge. See:
              http://www.redrok.com/images/beamstepper4.gif
               
              Yup, Looks kinda "clunky" by comparison to your half bridge version. I have a gut feeling that the latter circuit can be further simplified.
               
              wilf
               
               
               
               
              ----- Original Message -----
              Sent: Tuesday, October 29, 2002 9:51 PM
              Subject: Re: [beam] Re: Beamish Stepper Motor Driver

              Hi Wilf;

              wilf_nv wrote:

              > Very nice (beamish) Duane!

              Thanks; I must have tried a dozen variations.
              This works the best and is quit reliable.

              ------8<---- (snipped)
            • Duane C. Johnson
              Hi Duane, ... Actually both oscillators are off most of the time. When the LED sensors are aimed at the sun they are in balance. and, in this case, the two
              Message 6 of 27 , Oct 30, 2002
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                Hi Duane,

                wilf_nv wrote:

                > I find I appreciate the fine points of a circuit design if
                > I try to write up a little description of operation. but no
                > better way to test a design than by actually building and
                > testing it "hands on". Anything weird or unusual popping
                > up (hmm, that's strange) should tweak your interest (not
                > frustration) cause it makes life interesting and often
                > leads to brand new ideas. You have obviously exploited
                > every possible quirk in this novel design.

                > I have one or two comments -

                > You said:

                > > 2. Essentially zero power consumption when not moving.

                > and

                > > Actually it doesn't make much difference what the floating
                > > voltage is. It can be in only three regions, high, low, or
                > > mid. This voltage tends to stay in what ever region it
                > >was actively set in.

                > With both oscillators off (i.e. at night),

                Actually both oscillators are off most of the time.
                When the LED sensors are aimed at the sun they are in balance.
                and, in this case, the two transistors, Q1-Q4, with the help
                of resisters, R1-R5, actively disable both oscillators.

                > a floating dc level in the RC network can potentially
                > maintain a stable state of one output low and the other
                > high causing continuous current flow through both motor
                > windings. If the input "leakage current" level and
                > direction is dependent on the Schmitt states, then opposite
                > output states would cause the floating dc level to drift
                > to a stable Vcc/2 potential which maintains that state.

                That's what I thought too. But it doesn't do it.
                No amount of fiddling with the inputs allows this to
                happen. Of course I can force it into this both on state
                but once I remove any external bias it reverts back to
                both both either high or low. Kind of bi-stable.
                I tries about 25 different 40106 gates and none
                performed badly.

                I suspect that one gate always becomes dominant
                and forces the other to be in the same state.

                One quirk that I do see though. Sometimes when the voltage
                is in the mid range the power supply current rises
                to one of two current levels. Either a lower value of
                about 301uA or higher 601uA as opposed to just 1uA idle
                current. The 300uA or 600uA portions are probably
                associated with one or both the Schmitt trigger transistors
                being in the linear region. The actual values are
                different for each gate tried.

                BTW, the above quirk usually doesn't happen because
                after the last oscillator pulse occurs the output
                tends to drive the floating phase shifter to one extreme
                or the other.

                > With external bias resistors setting the dc level, this
                > posibility can be avoided.

                The added bias resisters tend to just make the above
                quirk happen more often.

                > Then you speak righteously of :

                > > LEDs make marvelous light sensors. The green ones
                > > generate up to 1.7 volts. In the back to back
                > > arrangement this amounts to a 3.4 volt change. Quite
                > > enough to drive logic gates directly. If set at 90
                > > degrees to each other they have a high accuracy.
                > > You might think the voltage changes linearly with the
                > > differential illumination. This is not the case.
                > > Large voltage changers occur over a few degrees.

                > Marvelous indeed! The trick for using LED PV sensors is
                > to keep the load capacitance very low and load resistance
                > very high. I found that the LED photovoltaic current is
                > in the nA range while reverse leakage photo current is in
                > the uA range.

                I find that most LEDs generate quite a bit more current
                than a few nA. In fact the large LED I use in by trackers,
                a 10mm LUMEX SSL-LX100133XGC, can generate up to 170uA
                of current when aimed directly at the sun. and about
                10 to 20 uA when at 45 degrees. Smaller LEDs generate
                much lower current, in the few uA.

                I have been working on a single solar cell power boost
                circuit that uses 2 or 3 of these LEDs as a bootstrap
                power supply to get it started. See:
                http://www.redrok.com/images/pvcellinv01.gif

                > I am looking at 5x7 LED arrays for simple imaging
                > applications so I am curious about the light to
                > voltage response curve. Silicon photodiodes have a well
                > known log response. You described large voltage changes
                > in terms of "a few degrees". That can be for several
                > reasons (ie shadow edges).

                It isn't shadows. I can increase the sensitivity to
                about +-1/4 degree with a shadow blocker. But it
                is a few degrees without the shadow.

                > Any ideas why the non-linear differential response to
                > light levels for dual reversed LED sensors?

                I like to describe the LED pair as kind of fighting
                with each other. They are both illuminated about evenly.
                Each trying to produce current. However little current
                is generated so, except when a load is present.
                Which ever wins expresses its voltage polarity.
                In CMOS circuits the load current is almost non existent.
                So the voltage swing is large. In bipolar circuits there
                is only a small load so the voltage swing is still fairly
                large. This change from one being dominant to the
                other is very directionally sensitive in the pair.

                The green LEDs use exotic semiconductors which have
                large bandgap voltages. In this case about 1.7V.
                I have tried blue LEDs which generate a little under
                3 volts. I haven't tried the new ultra violet LEDs yet
                which may be in the 5 volt range. However, the blue
                or UV leds are much more expensive and the solar
                spectrum is somewhat deficient in these wavelengths
                so I don't use them for solar trackers because of
                the low output current.

                > > I just posted the other variant with H-Bridge. See:
                > > http://www.redrok.com/images/beamstepper4.gif

                > Yup, Looks kinda "clunky" by comparison to your half
                > bridge version. I have a gut feeling that the latter
                > circuit can be further simplified.

                I will try the 74AC14 later today. But the AC14 input
                is not as asymmetrical. The oscillator is easy to get
                a square output. I am worried that the non symmetrical
                input will affect the phase shifting part. There isn't
                a way to get the phase shifter to be symmetrical though.

                The AC14 could drive the stepper directly.

                Here are a few other LED circuits.
                Blatant plug here, I sell most of these things but
                don't mind people building their own.
                http://www.redrok.com/electron.htm#tracker
                An analog H-bridge driver.
                http://www.redrok.com/electron.htm#led5
                An older design with 4 LEDs and CMOS gates.
                http://www.redrok.com/electron.htm#ledshex3
                High power version with 2 LED bipolar sensor.
                http://www.redrok.com/led3xassm.htm
                And others.
                I'm now working on an AC powered tracker that
                drives TV antenna rotators. And is dual axis.

                > wilf

                Duane

                --
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              • wilf_nv
                Thanks for doing all the hard work there Duane, interesting results. some small comments in line mostly to show my orginal questions were not too naive. ...
                Message 7 of 27 , Oct 30, 2002
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                  Thanks for doing all the hard work there Duane, interesting results.

                  some small comments in line mostly to show my orginal questions were
                  not too naive.

                  --- In beam@y..., "Duane C. Johnson" <redrok@r...> wrote:

                  > > With both oscillators off (i.e. at night),
                  >
                  > Actually both oscillators are off most of the time.

                  For solar tracking yes, both oscillators are mostly off, and just one
                  oscillator is activivated periodically throughout the day to jog the
                  array westward. The other oscillator probably operates just once a
                  day, just long enough to return the array to the east sky. Total
                  number of pulses per day from each oscillator should be about equal.

                  > > opposite
                  > > output states would cause the floating dc level to drift
                  > > to a stable Vcc/2 potential which maintains that state.

                  > That's what I thought too. But it doesn't do it.
                  > No amount of fiddling with the inputs allows this to
                  > happen. Of course I can force it into this both on state
                  > but once I remove any external bias it reverts back to
                  > both both either high or low. Kind of bi-stable.
                  > I tries about 25 different 40106 gates and none
                  > performed badly.

                  This is why "direct experiment" wins over "thought experiment" hands
                  down. These subtle hidden features of various electronic devices are
                  an untapped goldmine for designers but are rarely exploited. If it
                  is not in the data sheet it can't be used. Of course the manufacturer
                  may change his process without affecting the listed specifications
                  but drastically change the more subtle features. Best strategy is to
                  use a mature part they won't spend more money on developing.

                  The same sort of argument goes for using "undocumented opcodes" in
                  CPUs. (did I get the attention of some sofware guys?)


                  > One quirk that I do see though. Sometimes when the voltage
                  > is in the mid range the power supply current rises
                  > to one of two current levels. Either a lower value of
                  > about 301uA or higher 601uA as opposed to just 1uA idle
                  > current. The 300uA or 600uA portions are probably
                  > associated with one or both the Schmitt trigger transistors
                  > being in the linear region. The actual values are
                  > different for each gate tried.

                  This will be more of a concern for 74ACxx devices. I have measured
                  supply current rising to >50ma when the input voltage is in a narrow
                  region near the switching threshold.

                  >
                  > BTW, the above quirk usually doesn't happen because
                  > after the last oscillator pulse occurs the output
                  > tends to drive the floating phase shifter to one extreme
                  > or the other.

                  Same reason that suspended bicore normally don't hang up( but can
                  easily be forced to hang)

                  > > With external bias resistors setting the dc level, this
                  > > posibility can be avoided.

                  > The added bias resisters tend to just make the above
                  > quirk happen more often.

                  I bet I could design it so it doesn't cause the quirk at all.

                  > > Then you speak righteously of :
                  >
                  > > > LEDs make marvelous light sensors. The green ones


                  > I find that most LEDs generate quite a bit more current
                  > than a few nA. In fact the large LED I use in by trackers,
                  > a 10mm LUMEX SSL-LX100133XGC, can generate up to 170uA
                  > of current when aimed directly at the sun. and about
                  > 10 to 20 uA when at 45 degrees. Smaller LEDs generate
                  > much lower current, in the few uA.

                  Indoor vs outdoor tests.

                  > I have been working on a single solar cell power boost
                  > circuit that uses 2 or 3 of these LEDs as a bootstrap
                  > power supply to get it started. See:
                  > http://www.redrok.com/images/pvcellinv01.gif

                  I have mentioned this low current bootstrap method also to kick start
                  sub 1V inverters


                  > > Any ideas why the non-linear differential response to
                  > > light levels for dual reversed LED sensors?
                  >
                  > I like to describe the LED pair as kind of fighting
                  > with each other.

                  > > the latter
                  > > circuit can be further simplified.
                  >
                  > I will try the 74AC14 later today. But the AC14 input
                  > is not as asymmetrical. The oscillator is easy to get
                  > a square output. I am worried that the non symmetrical
                  > input will affect the phase shifting part. There isn't
                  > a way to get the phase shifter to be symmetrical though.

                  There way to achieve 50% duty cycle in a simple 2 inverter CMOS
                  oscillator is to avoid clamping the positive feedback signal in the
                  input diodes using a 10X series input resistor
                • Gord Mitchell
                  Hey Wilf What chip is used in the stepper head and is there a scematic that shows the chip pin outs....? Gord ...
                  Message 8 of 27 , Oct 30, 2002
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                    Hey Wilf

                    What chip is used in the stepper head and is there a scematic that
                    shows the chip pin outs....?

                    Gord


                    >
                    > I just posted the other variant with H-Bridge. See:
                    > http://www.redrok.com/images/beamstepper4.gif
                    >
                    > Yup, Looks kinda "clunky" by comparison to your half bridge version.
                    > I have a gut feeling that the latter circuit can be further
                    > simplified.
                    >
                    > wilf
                    >
                    >
                    >
                    >
                    > ----- Original Message -----
                    > From: Duane C. Johnson
                    > To: beam@yahoogroups.com
                    > Sent: Tuesday, October 29, 2002 9:51 PM
                    > Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                    >
                    >
                    > Hi Wilf;
                    >
                    > wilf_nv wrote:
                    >
                    > > Very nice (beamish) Duane!
                    >
                    > Thanks; I must have tried a dozen variations.
                    > This works the best and is quit reliable.
                    >
                    > ------8<---- (snipped)


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                  • Mycroft2152
                    Hi Gord, Check out the digikey website for part #40106. the info is there Myc Gord Mitchell wrote:Hey Wilf What chip is used in the
                    Message 9 of 27 , Oct 30, 2002
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                      Hi Gord,

                      Check out the digikey website for part #40106. the info is there

                      Myc

                       Gord Mitchell <gord_1812@...> wrote:

                      Hey Wilf

                      What chip is used in the stepper head and is there a scematic that
                      shows the chip pin outs....? 

                      Gord


                      >
                      > I just posted the other variant with H-Bridge. See:
                      > http://www.redrok.com/images/beamstepper4.gif
                      >
                      > Yup, Looks kinda "clunky" by comparison to your half bridge version.
                      > I have a gut feeling that the latter circuit can be further
                      > simplified.
                      >
                      > wilf
                      >
                      >
                      >
                      >
                      > ----- Original Message -----
                      >   From: Duane C. Johnson
                      >   To: beam@yahoogroups.com
                      >   Sent: Tuesday, October 29, 2002 9:51 PM
                      >   Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                      >
                      >
                      >   Hi Wilf;
                      >
                      >   wilf_nv wrote:
                      >
                      >   > Very nice (beamish) Duane!
                      >
                      >   Thanks; I must have tried a dozen variations.
                      >   This works the best and is quit reliable.
                      >
                      >   ------8<---- (snipped)


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                    • Duane C. Johnson
                      Hi Gord; It is a conventional B series 40106 CMOS hex Schmitt trigger inverting buffer. The pin out is on the schematic. It has the same pin out as a 7414. ...
                      Message 10 of 27 , Oct 30, 2002
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                        Hi Gord;

                        It is a conventional B series 40106 CMOS
                        hex Schmitt trigger inverting buffer.

                        The pin out is on the schematic.

                        It has the same pin out as a 7414.

                        Gord Mitchell wrote:

                        > Hey Wilf

                        > What chip is used in the stepper head and is there
                        > a scematic that shows the chip pin outs....?

                        http://www.redrok.com/images/beamstepper3.gif
                        http://www.redrok.com/images/beamstepper4.gif

                        > Gord

                        Duane

                        --
                        Home of the $35 LED solar tracker.
                        http://www.redrok.com/electron.htm#led3
                        CUL8ER \ \ \ \ \ \\ \ \ Receiver
                        Powered by\ \ \ \ \ \\ \ \ [*]
                        Thermonuclear \ \Solar\Energy\from the Sun \ /////|
                        Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
                        \ \ \ \ \ /\ / \/ / / / |
                        WA0VBE \ \ \ \ / /\ \/ / / \/ /|
                        Ziggy \ \ \/ / / \ \/ \/ /\ |
                        \ / \ \/ / /\ \\ / \ / / |
                        "Red Rock Energy" === ===\ / \ / \ === \ / ===
                        Duane C. Johnson, Designer=== === \ \ === / |
                        1825 Florence St Mirrors,Heliostats,Controls & Mounts|
                        White Bear Lake, Minnesota \ \ / |
                        USA 55110-3364 \ \ |
                        (651)635-5O65 work \ \ / |
                        (651)426-4766 home use Courier New Font \ \ |
                        (413)556-659O Fax copyright \ / |
                        (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
                        redrok@... (my primary email: address) \ |
                        redrok2@... (Hotmail address) \ |
                        duane.johnson@... (Unisys address) \ |
                        http://www.redrok.com/index.htm (My New Web site) \|
                        These are my opinions, and not that of Unisys Corp. ===
                      • Duane C. Johnson
                        Hi Wilf; ... That would be nice. ... The higher currents are definitely outdoors. I do most testing indoors on my circuits with a fluorescent ceiling light.
                        Message 11 of 27 , Oct 30, 2002
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                          Hi Wilf;

                          wilf_nv wrote:

                          > Thanks for doing all the hard work there Duane,
                          > interesting results.

                          > some small comments in line mostly to show my
                          > orginal questions were not too naive.

                          > --- In beam@y..., "Duane C. Johnson" <redrok@r...> wrote:

                          > > > With both oscillators off (i.e. at night),

                          > > Actually both oscillators are off most of the time.

                          > For solar tracking yes, both oscillators are mostly off,
                          > and just one oscillator is activivated periodically
                          > throughout the day to jog the array westward. The other
                          > oscillator probably operates just once a day, just long
                          > enough to return the array to the east sky. Total
                          > number of pulses per day from each oscillator should be
                          > about equal.

                          > > > opposite
                          > > > output states would cause the floating dc level to
                          > > > drift to a stable Vcc/2 potential which maintains
                          > > > that state.

                          > > That's what I thought too. But it doesn't do it.
                          > > No amount of fiddling with the inputs allows this to
                          > > happen. Of course I can force it into this both on
                          > > state but once I remove any external bias it reverts
                          > > back to both both either high or low. Kind of
                          > > bi-stable. I tries about 25 different 40106 gates
                          > > and none performed badly.

                          > This is why "direct experiment" wins over "thought
                          > experiment" hands down. These subtle hidden features
                          > of various electronic devices are an untapped goldmine
                          > for designers but are rarely exploited. If it is not
                          > in the data sheet it can't be used. Of course the
                          > manufacturer may change his process without affecting
                          > the listed specifications but drastically change the
                          > more subtle features. Best strategy is to use a mature
                          > part they won't spend more money on developing.

                          > The same sort of argument goes for using "undocumented
                          > opcodes" in CPUs. (did I get the attention of some
                          > sofware guys?)

                          > > One quirk that I do see though. Sometimes when the
                          > > voltage is in the mid range the power supply current
                          > > rises to one of two current levels. Either a lower
                          > > value of about 301uA or higher 601uA as opposed to
                          > > just 1uA idle current. The 300uA or 600uA portions
                          > > are probably associated with one or both the Schmitt
                          > > trigger transistors being in the linear region. The
                          > > actual values are different for each gate tried.

                          > This will be more of a concern for 74ACxx devices.
                          > I have measured supply current rising to >50ma when
                          > the input voltage is in a narrow region near the
                          > switching threshold.

                          > > BTW, the above quirk usually doesn't happen because
                          > > after the last oscillator pulse occurs the output
                          > > tends to drive the floating phase shifter to one extreme
                          > > or the other.

                          > Same reason that suspended bicore normally don't hang
                          > up( but can easily be forced to hang)

                          > > > With external bias resistors setting the dc level,
                          > > > this posibility can be avoided.

                          > > The added bias resisters tend to just make the above
                          > > quirk happen more often.

                          > I bet I could design it so it doesn't cause the quirk
                          > at all.

                          That would be nice.

                          > > > Then you speak righteously of :

                          > > > > LEDs make marvelous light sensors. The green ones

                          > > I find that most LEDs generate quite a bit more current
                          > > than a few nA. In fact the large LED I use in by trackers,
                          > > a 10mm LUMEX SSL-LX100133XGC, can generate up to 170uA
                          > > of current when aimed directly at the sun. and about
                          > > 10 to 20 uA when at 45 degrees. Smaller LEDs generate
                          > > much lower current, in the few uA.

                          > Indoor vs outdoor tests.

                          The higher currents are definitely outdoors. I do most testing
                          indoors on my circuits with a fluorescent ceiling light.

                          > > I have been working on a single solar cell power boost
                          > > circuit that uses 2 or 3 of these LEDs as a bootstrap
                          > > power supply to get it started. See:
                          > > http://www.redrok.com/images/pvcellinv01.gif

                          > I have mentioned this low current bootstrap method also
                          > to kick start sub 1V inverters

                          The above inverter had to run at .55 volts and
                          up to about 4 amps.

                          > > > Any ideas why the non-linear differential response to
                          > > > light levels for dual reversed LED sensors?

                          > > I like to describe the LED pair as kind of fighting
                          > > with each other.

                          > > > the latter
                          > > > circuit can be further simplified.

                          > > I will try the 74AC14 later today. But the AC14 input
                          > > is not as asymmetrical. The oscillator is easy to get
                          > > a square output. I am worried that the non symmetrical
                          > > input will affect the phase shifting part. There isn't
                          > > a way to get the phase shifter to be symmetrical though.

                          > There way to achieve 50% duty cycle in a simple 2 inverter
                          > CMOS oscillator is to avoid clamping the positive feedback
                          > signal in the input diodes using a 10X series input resistor

                          The 74AC14 is a very different animal from the 40106
                          or even a 74HC14. I couldn't get it to work well at
                          all.

                          What's the deal with the 1 inverter oscillator.
                          Sometimes it runs sometimes not. It kind of gets
                          stuck. The stuck condition seems related other gates
                          that may be near their threshold.

                          You mentioned the 2 inverter design. Are Schmitt trigger
                          oscillators un reliable in "AC"?

                          Duane

                          --
                          Home of the $35 LED solar tracker.
                          http://www.redrok.com/electron.htm#led3
                          CUL8ER \ \ \ \ \ \\ \ \ Receiver
                          Powered by\ \ \ \ \ \\ \ \ [*]
                          Thermonuclear \ \Solar\Energy\from the Sun \ /////|
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                          \ \ \ \ \ /\ / \/ / / / |
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                          Ziggy \ \ \/ / / \ \/ \/ /\ |
                          \ / \ \/ / /\ \\ / \ / / |
                          "Red Rock Energy" === ===\ / \ / \ === \ / ===
                          Duane C. Johnson, Designer=== === \ \ === / |
                          1825 Florence St Mirrors,Heliostats,Controls & Mounts|
                          White Bear Lake, Minnesota \ \ / |
                          USA 55110-3364 \ \ |
                          (651)635-5O65 work \ \ / |
                          (651)426-4766 home use Courier New Font \ \ |
                          (413)556-659O Fax copyright \ / |
                          (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
                          redrok@... (my primary email: address) \ |
                          redrok2@... (Hotmail address) \ |
                          duane.johnson@... (Unisys address) \ |
                          http://www.redrok.com/index.htm (My New Web site) \|
                          These are my opinions, and not that of Unisys Corp. ===
                        • Wilf Rigter
                          Hi Duane, Here is the schematic for the 50% duty cycle 74AC14 oscillator I mentioned. The trick is Rx which prevents the normal dc restoration to Vcc/2 of the
                          Message 12 of 27 , Oct 30, 2002
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                            Hi Duane,
                             
                            Here is the schematic for the 50% duty cycle 74AC14 oscillator I mentioned. The trick is Rx which prevents the normal dc restoration to Vcc/2  of the AC feedback signal clamped by input protection diodes. As a result, for  Vcc =  5V the waveform at Tp1 is about 11Vp-p.  (that waveform can be rectified and can provide a low current +8V/-3V auxillary voltage for ??)   The average DC voltage at Tp1 is midway between the upper and lower Schmitt thresholds. That causes the dutycycle to be close to 50% regardless of the actual threhold levels. Rx should be at least 10 times R2. The components shown should give about the same frequency as the original circuit but adjust as required. Hopefully you can find a useful stepper motor can be driven directly from the 74AC14 outputs. Note the oops for Q1.
                             
                             
                             
                            wilf

                             
                             
                             
                             
                            ----- Original Message -----
                            From: wilf_nv
                            Sent: Wednesday, October 30, 2002 7:17 AM
                            Subject: [beam] Re: Beamish Stepper Motor Driver


                            The way to achieve 50% duty cycle in a simple 2 inverter CMOS oscillator is to avoid clamping the positive feedback signal in the input diodes using a 10X series input resistor.




                          • Wilf Rigter
                            First I want to mention that Duane s circuits are some of the most innovative and elegant designs I have had the pleasure to learn from and I highly recommend
                            Message 13 of 27 , Oct 30, 2002
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                              First I want to mention that Duane's circuits are some of the most innovative and elegant designs I have had the pleasure to learn from and I highly recommend adapting them to BEAM robot applications.   Duane also points out that some of his ideas came from BEAM. What goes round, comes round.
                               
                              So Duane, here is some in line feedback on last reply:
                               
                              ----- Original Message -----
                              Sent: Wednesday, October 30, 2002 7:31 PM
                              Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                              snip

                              > I bet I could design it so it doesn't cause the quirk
                              > at all.

                              That would be nice.
                              I'm going to build and test the circuit this weekend.

                              > > http://www.redrok.com/images/pvcellinv01.gif

                              > I have mentioned this low current bootstrap method also
                              > to kick start sub 1V inverters
                              The comment was with respect to a National 5V converter chip that starts at 0.8V
                              but operates down to below 0.5V. I suggested this could be used with a single
                              aerospace type PV cell (0.55V) if the circuit was bootstrapped with some small
                              series PV cells. Just some blue sky talk is all..

                              >The above inverter had to run at .55 volts and
                              >up to about 4 amps.
                              >The 74AC14 is a very different animal from the 40106
                              >or even a 74HC14. I couldn't get it to work well at
                              >all.

                              The AC14 inverters are probably oscillating at 100MHz caused by negative feedback through
                              output to input pin stray capacitance.  The series inductance of the RC component leads is a
                              high impedance at that frequency. Components leads must be kept short and a groundplane
                              is recommended. Using 2 inverters with positive feedback should swamp out the problem.
                              Come to think of it, because of that the Rx resistor I recommended may not work well with AC14
                              unless a small cap (100pf) is placed in parallel with Rx.  Anyway the thresholds are reasonable
                              symmetrical and perhaps Rx can be omitted.

                              >What's the deal with the 1 inverter oscillator.
                              >Sometimes it runs sometimes not. It kind of gets
                              >stuck. The stuck condition seems related other gates
                              >that may be near their threshold.

                              >You mentioned the 2 inverter design. Are Schmitt trigger
                              >oscillators un reliable in "AC"?

                              Duane

                              --
                            • Duane C. Johnson
                              ... I tried this out and it works well. See: http://www.redrok.com/images/beamstepper5.gif The sensor front end works as described before. The floating phase
                              Message 14 of 27 , Nov 1, 2002
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                                > Hi Duane,

                                > Here is the schematic for the 50% duty cycle 74AC14 oscillator
                                > I mentioned. The trick is Rx which prevents the normal dc
                                > restoration to Vcc/2 of the AC feedback signal clamped by
                                > input protection diodes. As a result, for Vcc = 5V the
                                > waveform at Tp1 is about 11Vp-p.
                                > (that waveform can be rectified and can provide a low
                                > current +8V/-3V auxillary voltage for ??)
                                > The average DC voltage at Tp1 is midway between the upper
                                > and lower Schmitt thresholds. That causes the dutycycle to
                                > be close to 50% regardless of the actual threhold levels.
                                > Rx should be at least 10 times R2. The components shown
                                > should give about the same frequency as the original
                                > circuit but adjust as required. Hopefully you can find a
                                > useful stepper motor can be driven directly from the
                                > 74AC14 outputs. Note the oops for Q1.

                                I tried this out and it works well. See:
                                http://www.redrok.com/images/beamstepper5.gif

                                The sensor front end works as described before.

                                The floating phase shifter didn't work at all so I
                                added a voltage divider to center the voltage on
                                U1D & U1C to the mid threshold point and the 2 half
                                bridges worked. However when in the stationary mode
                                the idle current was greater than 10mA due to the
                                74AC14 Schmitt being in the linear region.

                                To fix this I realized that lower half of the voltage
                                divider could be connected to the output of the
                                oscillators.

                                Lets say the upper oscillator is off and the bottom
                                is outputting 50%. The average of these is 25%.
                                The resisters R9, R10, and R11 now bias to the
                                threshold and I get a reasonable quadriture signal
                                to the stepper.

                                When both oscillators are off the average is 0% which
                                biases the voltage to a lower voltage. This reduces
                                the idle current to about .4mA or so. Now I'm happy.

                                It would be nice to get the idle current to zero but
                                I can't get the simple divider to bring the bias voltage
                                any lower without upsetting the quadriture relationship.

                                A more complicated arrangement with 2 diodes does bring
                                the idle current to zero but not worth the extra
                                complexity.

                                One negative. The 2 inverter oscillators consume
                                4 inverters. I now don't have 2 more for driving the
                                stepper with full bridges.

                                Would the 74AC240 octal inverting buffer work in a similar
                                way to the 74AC14? The 2 inverter oscillator doesn't need
                                Schmitt inputs to work. Plus I can possibly use the tristate
                                feature to remove power from the stepper when not moving.

                                Thanks for the help.

                                > wilf

                                Duane

                                --
                                Home of the $35 LED solar tracker.
                                http://www.redrok.com/electron.htm#led3
                                CUL8ER \ \ \ \ \ \\ \ \ Receiver
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                                Thermonuclear \ \Solar\Energy\from the Sun \ /////|
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                                WA0VBE \ \ \ \ / /\ \/ / / \/ /|
                                Ziggy \ \ \/ / / \ \/ \/ /\ |
                                \ / \ \/ / /\ \\ / \ / / |
                                "Red Rock Energy" === ===\ / \ / \ === \ / ===
                                Duane C. Johnson, Designer=== === \ \ === / |
                                1825 Florence St Mirrors,Heliostats,Controls & Mounts|
                                White Bear Lake, Minnesota \ \ / |
                                USA 55110-3364 \ \ |
                                (651)635-5O65 work \ \ / |
                                (651)426-4766 home use Courier New Font \ \ |
                                (413)556-659O Fax copyright \ / |
                                (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
                                redrok@... (my primary email: address) \ |
                                redrok2@... (Hotmail address) \ |
                                duane.johnson@... (Unisys address) \ |
                                http://www.redrok.com/index.htm (My New Web site) \|
                                These are my opinions, and not that of Unisys Corp. ===
                              • Duane C. Johnson
                                Hi All; Wilf and I have been developing another solar tracker that is based on a 74AC240 Dual Quad Tristate Buffer. There have been a number of variations.
                                Message 15 of 27 , Nov 9, 2002
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                                  Hi All;

                                  Wilf and I have been developing another solar tracker
                                  that is based on a 74AC240 Dual Quad Tristate Buffer.
                                  There have been a number of variations. This is
                                  the results. See:
                                  http://www.redrok.com/images/beamstepper7e.gif

                                  The 74AC240 stepper driver works by enabling each half
                                  of the buffer. Only one half can be enabled at a time.

                                  Let's assume that the top half of the driver is enabled.
                                  U1A & U1B along with R8, C1, & the input protection
                                  resister R7 form a square wave oscillator. The outputs
                                  of U1A & U1B directly drive one coil of a bipolar stepper
                                  motor.

                                  U1C & U1D along with R9, C2, & the input protection
                                  resister R10 form a 90 degree phase shift. The outputs
                                  of U1C & U1D directly drive the other coil of the bipolar
                                  stepper motor. The motor turns in one direction.

                                  If the second bottom half of the driver is enabled the
                                  oscillator using U1E & U1F work as before. U1H & U1G
                                  along with R12, C3, & the input protection
                                  resister R11 form a 90 degree phase shift. Except it's
                                  connected the other way around from before so it's
                                  actually 270 degrees. The outputs of U1H & U1G directly
                                  drive the other coil of the bipolar stepper motor. The
                                  motor turns in the other direction. Neat, Huh!

                                  An earlier version of the circuit didn't work well
                                  because the the sensors presented an analog enable
                                  signal. This was sometimes at the threshold voltage
                                  which caused the buffer to have high idle current and
                                  sometimes cross coupling which was a bad thing. %^(

                                  What was needed was a sensor that had a Schmitt trigger
                                  input. This could be done using a Schmitt trigger gate
                                  which works well. I suggest a 40106 or 74AHCT14. However,
                                  this needs a second IC.

                                  A better solution is to make the sensor have Schmitt
                                  action. The first version was:
                                  http://www.redrok.com/images/beamstepper7a.gif
                                  The problem was that it worked over a limited voltage
                                  range.

                                  http://www.redrok.com/images/beamstepper7e.gif
                                  works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                  latch similar in operation to an SCR.

                                  Let's start with the left side without the LEDs.
                                  Initially no current flows. The series resisters
                                  R5 & R2 cause a small bias current to flow in the base
                                  of Q1. Which pass current through R1 causing Q3 to
                                  conduct. Since Q3 shorts out R5 the current through
                                  R2 doubles. The output at the collector of Q1 snaps
                                  high disabling the connected buffer.

                                  (Note, R5 & R6 aren't actually required. It turns
                                  out that leakage currents in the transistors is enough
                                  to get started. I tried many transistors and never found
                                  one that didn't work as expected. Prudent circuit design
                                  demands that R5 & R6 be included because one might find
                                  a transistor that is so perfect it won't work. Bummer. )

                                  The now connected and lit LED1 has the ability to
                                  absorb the current through R2 starving Q1 which
                                  switches off resulting in the output snapping low.
                                  Q3 also switches off reducing the bias current
                                  in R2 to 1/2. This condition persists until the
                                  LED goes dark.

                                  You might ask where the current for the other side of
                                  the LED comes from. It is from base of Q2 on the right
                                  side. Actually, when the left side is turned off the
                                  right side is turned on doubly as the current from
                                  both R2 and R3 go through the base.

                                  The right side works the same way. Since the LEDs
                                  are connected anti parallel only one latch can
                                  be off at a time. This is safe for the buffers.

                                  When both of the quad buffers are supposed to be off
                                  it is essential that all inputs not be near the
                                  threshold to have the lowest idle current. R13 & R14
                                  ensure that all inputs be near ground. All inputs
                                  are connected to R13 or R14 either directly, through
                                  input resisters, or through the stepper motor. I
                                  added R15 & R16 for testing when the stepper motor
                                  is disconnected. If the motor is permanently
                                  connected R15 & R16 aren't needed. R13 & R14 can also
                                  be connected to VCC. They don't even need to be to
                                  the same voltage, although it operates quicker if
                                  they are the same.

                                  I have tested this circuit with about 25 different
                                  74AC240s. They all worked as expected.

                                  I ran the circuit from about 2.4V to 8.5V.
                                  OK, one shouldn't go past 7V to be within the specs
                                  of the 74AC240.

                                  The sensor section was tested to 40V. It still works
                                  well, the sensitivity is less because the bias current
                                  is proportional to voltage which requires brighter
                                  illumination to work.

                                  The step patterns are not perfectly symmetrical because
                                  this is essentially an analog circuit. Some resister
                                  adjustment can be done.

                                  To change the speed of the motor adjust the capacitor
                                  values. Note, all three need to be the same value.

                                  I have chosen the time constants of R9-C2 & R12-C3
                                  to be about 3/4ths of R8-C1. Try to keep these ratios.
                                  ( BTW, I'm not sure this is the exact ratio but it
                                  seams about right. )

                                  The 10M resisters in the sensor are the largest
                                  commonly available resisters in 1/8W size. I tried
                                  22M in 1/4W and that worked well with added
                                  sensitivity. I suppose if you could find 100M they
                                  would work even better.

                                  I have a variation which is even more sensitive to
                                  low light levels. Ask me if you want this variation.

                                  I have to thank Wilf for his invaluable help in the
                                  circuit design. Thanks Wilf.

                                  Have fun, Duane

                                  --
                                  Home of the $35 LED solar tracker.
                                  http://www.redrok.com/electron.htm#led3
                                  CUL8ER \ \ \ \ \ \\ \ \ Receiver
                                  Powered by\ \ \ \ \ \\ \ \ [*]
                                  Thermonuclear \ \Solar\Energy\from the Sun \ /////|
                                  Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
                                  \ \ \ \ \ /\ / \/ / / / |
                                  WA0VBE \ \ \ \ / /\ \/ / / \/ /|
                                  Ziggy \ \ \/ / / \ \/ \/ /\ |
                                  \ / \ \/ / /\ \\ / \ / / |
                                  "Red Rock Energy" === ===\ / \ / \ === \ / ===
                                  Duane C. Johnson, Designer=== === \ \ === / |
                                  1825 Florence St Mirrors,Heliostats,Controls & Mounts|
                                  White Bear Lake, Minnesota \ \ / |
                                  USA 55110-3364 \ \ |
                                  (651)635-5O65 work \ \ / |
                                  (651)426-4766 home use Courier New Font \ \ |
                                  (413)556-659O Fax copyright \ / |
                                  (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
                                  redrok@... (my primary email: address) \ |
                                  redrok2@... (Hotmail address) \ |
                                  duane.johnson@... (Unisys address) \ |
                                  http://www.redrok.com/index.htm (My New Web site) \|
                                  These are my opinions, and not that of Unisys Corp. ===
                                • Wilf Rigter
                                  have been chomping at the bit for Duane to post this new design. This is truly a mindmeld of Duane s own unique circuit designs and beam. A great example of
                                  Message 16 of 27 , Nov 9, 2002
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                                     have been chomping at the bit for Duane to post this new design. This is
                                    truly a "mindmeld" of Duane's own unique circuit designs and beam. A great
                                    example of technological hybrid vitality, this Beamish SMD circuit is
                                    perfect for solar tracker applications in it's own right and also opens the
                                    door to many other beam applications.  The detailed description of operation
                                    makes this article a complete tutorial for designing with this circuit. The
                                    variations of the LED detector shows how a just a few components can be used
                                    to create a multitude of useful crcuits, that can be plugged into your own
                                    circuit designs .

                                    Beam historians might recognize the core of the stepper design as the Master
                                    Slave Monocore,  I first dabbled with in 1999 but which Mark Tilden invented
                                    earlier with his  "robustness test", demonstrating that an MS Bicore keeps
                                    on ticking despite the removal of some components. Still earlier, this
                                    oscillator circuit could be found as a textbook example in CMOS Logic Data
                                    handbooks (Yikes, I remember when CMOS, invented by Al Medwin of RCA, was
                                    introduced in the mid 60s).

                                    As an example of other applications, you can use the oscillator, phase
                                    shifter and phase reverser  for driving two independent gear motors of a
                                    walker as an alternative to a reversing MS bicore circuit.

                                    Lots more to come,

                                    wilf

                                    ----- Original Message -----
                                    From: "Duane C. Johnson" <redrok@...>
                                    To: <beam@yahoogroups.com>
                                    Cc: "wilf_nv" <wrigter@...>
                                    Sent: Saturday, November 09, 2002 9:08 AM
                                    Subject: Re: [beam] Re: Beamish Stepper Motor Driver


                                    > Hi All;
                                    >
                                    > Wilf and I have been developing another solar tracker
                                    > that is based on a 74AC240 Dual Quad Tristate Buffer.
                                    > There have been a number of variations. This is
                                    > the results. See:
                                    > http://www.redrok.com/images/beamstepper7e.gif
                                    >
                                     
                                  • Wilf Rigter
                                    My memory being somewhat fuzzy on this, CMOS was actually invented in the early 70 s. wilf ... From: Wilf Rigter To: beam@yahoogroups.com Sent: Saturday,
                                    Message 17 of 27 , Nov 9, 2002
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                                      My memory being somewhat fuzzy on this,  CMOS was actually invented in the early 70's.
                                       
                                      wilf

                                      ----- Original Message -----
                                      Sent: Saturday, November 09, 2002 11:53 AM
                                      Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                       have been chomping at the bit for Duane to post this new design. This is
                                      truly a "mindmeld" of Duane's own unique circuit designs and beam. A great
                                      example of technological hybrid vitality, this Beamish SMD circuit is
                                      perfect for solar tracker applications in it's own right and also opens the
                                      door to many other beam applications.  The detailed description of operation
                                      makes this article a complete tutorial for designing with this circuit. The
                                      variations of the LED detector shows how a just a few components can be used
                                      to create a multitude of useful crcuits, that can be plugged into your own
                                      circuit designs .

                                      Beam historians might recognize the core of the stepper design as the Master
                                      Slave Monocore,  I first dabbled with in 1999 but which Mark Tilden invented
                                      earlier with his  "robustness test", demonstrating that an MS Bicore keeps
                                      on ticking despite the removal of some components. Still earlier, this
                                      oscillator circuit could be found as a textbook example in CMOS Logic Data
                                      handbooks (Yikes, I remember when CMOS, invented by Al Medwin of RCA, was
                                      introduced in the mid 60s).

                                      As an example of other applications, you can use the oscillator, phase
                                      shifter and phase reverser  for driving two independent gear motors of a
                                      walker as an alternative to a reversing MS bicore circuit.

                                      Lots more to come,

                                      wilf

                                      ----- Original Message -----
                                      From: "Duane C. Johnson" <redrok@...>
                                      To: <beam@yahoogroups.com>
                                      Cc: "wilf_nv" <wrigter@...>
                                      Sent: Saturday, November 09, 2002 9:08 AM
                                      Subject: Re: [beam] Re: Beamish Stepper Motor Driver


                                      > Hi All;
                                      >
                                      > Wilf and I have been developing another solar tracker
                                      > that is based on a 74AC240 Dual Quad Tristate Buffer.
                                      > There have been a number of variations. This is
                                      > the results. See:
                                      > http://www.redrok.com/images/beamstepper7e.gif
                                      >
                                       

                                      To unsubscribe from this group, send an email to:
                                      beam-unsubscribe@egroups.com



                                      Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
                                    • Wilf Rigter
                                      Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the
                                      Message 18 of 27 , Nov 9, 2002
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                                        Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.
                                         
                                         
                                        ---- Original Message -----
                                        Sent: Saturday, November 09, 2002 9:08 AM
                                        Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                        Hi All;

                                        Wilf and I have been developing another solar tracker
                                        that is based on a 74AC240 Dual Quad Tristate Buffer.
                                        There have been a number of variations. This is
                                        the results. See:
                                        http://www.redrok.com/images/beamstepper7e.gif

                                        The 74AC240 stepper driver works by enabling each half
                                        of the buffer. Only one half can be enabled at a time.

                                        Let's assume that the top half of the driver is enabled.
                                        U1A & U1B along with R8, C1, & the input protection
                                        resister R7 form a square wave oscillator. The outputs
                                        of U1A & U1B directly drive one coil of a bipolar stepper
                                        motor.

                                        U1C & U1D along with R9, C2, & the input protection
                                        resister R10 form a 90 degree phase shift. The outputs
                                        of U1C & U1D directly drive the other coil of the bipolar
                                        stepper motor. The motor turns in one direction.

                                        If the second bottom half of the driver is enabled the
                                        oscillator using U1E & U1F work as before. U1H & U1G
                                        along with R12, C3, & the input protection
                                        resister R11 form a 90 degree phase shift. Except it's
                                        connected the other way around from before so it's
                                        actually 270 degrees. The outputs of U1H & U1G directly
                                        drive the other coil of the bipolar stepper motor. The
                                        motor turns in the other direction. Neat, Huh!

                                        An earlier version of the circuit didn't work well
                                        because the the sensors presented an analog enable
                                        signal. This was sometimes at the threshold voltage
                                        which caused the buffer to have high idle current and
                                        sometimes cross coupling which was a bad thing. %^(

                                        What was needed was a sensor that had a Schmitt trigger
                                        input. This could be done using a Schmitt trigger gate
                                        which works well. I suggest a 40106 or 74AHCT14. However,
                                        this needs a second IC.

                                        A better solution is to make the sensor have Schmitt
                                        action. The first version was:
                                        http://www.redrok.com/images/beamstepper7a.gif
                                        The problem was that it worked over a limited voltage
                                        range.

                                        http://www.redrok.com/images/beamstepper7e.gif
                                        works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                        latch similar in operation to an SCR.

                                        Let's start with the left side without the LEDs.
                                        Initially no current flows. The series resisters
                                        R5 & R2 cause a small bias current to flow in the base
                                        of Q1. Which pass current through R1 causing Q3 to
                                        conduct. Since Q3 shorts out R5 the current through
                                        R2 doubles. The output at the collector of Q1 snaps
                                        high disabling the connected buffer.

                                        (Note, R5 & R6 aren't actually required. It turns
                                        out that leakage currents in the transistors is enough
                                        to get started. I tried many transistors and never found
                                        one that didn't work as expected. Prudent circuit design
                                        demands that R5 & R6 be included because one might find
                                        a transistor that is so perfect it won't work. Bummer. )

                                        The now connected and lit LED1 has the ability to
                                        absorb the current through R2 starving Q1 which
                                        switches off resulting in the output snapping low.
                                        Q3 also switches off reducing the bias current
                                        in R2 to 1/2. This condition persists until the
                                        LED goes dark.

                                        You might ask where the current for the other side of
                                        the LED comes from. It is from base of Q2 on the right
                                        side. Actually, when the left side is turned off the
                                        right side is turned on doubly as the current from
                                        both R2 and R3 go through the base.

                                        The right side works the same way. Since the LEDs
                                        are connected anti parallel only one latch can
                                        be off at a time. This is safe for the buffers.

                                        When both of the quad buffers are supposed to be off
                                        it is essential that all inputs not be near the
                                        threshold to have the lowest idle current. R13 & R14
                                        ensure that all inputs be near ground. All inputs
                                        are connected to R13 or R14 either directly, through
                                        input resisters, or through the stepper motor. I
                                        added R15 & R16 for testing when the stepper motor
                                        is disconnected. If the motor is permanently
                                        connected R15 & R16 aren't needed. R13 & R14 can also
                                        be connected to VCC. They don't even need to be to
                                        the same voltage, although it operates quicker if
                                        they are the same.

                                        I have tested this circuit with about 25 different
                                        74AC240s. They all worked as expected.

                                        I ran the circuit from about 2.4V to 8.5V.
                                        OK, one shouldn't go past 7V to be within the specs
                                        of the 74AC240.

                                        The sensor section was tested to 40V. It still works
                                        well, the sensitivity is less because the bias current
                                        is proportional to voltage which requires brighter
                                        illumination to work.

                                        The step patterns are not perfectly symmetrical because
                                        this is essentially an analog circuit. Some resister
                                        adjustment can be done.

                                        To change the speed of the motor adjust the capacitor
                                        values. Note, all three need to be the same value.

                                        I have chosen the time constants of R9-C2 & R12-C3
                                        to be about 3/4ths of R8-C1. Try to keep these ratios.
                                        ( BTW, I'm not sure this is the exact ratio but it
                                        seams about right. )

                                        The 10M resisters in the sensor are the largest
                                        commonly available resisters in 1/8W size. I tried
                                        22M in 1/4W and that worked well with added
                                        sensitivity. I suppose if you could find 100M they
                                        would work even better.

                                        I have a variation which is even more sensitive to
                                        low light levels. Ask me if you want this variation.

                                        I have to thank Wilf for his invaluable help in the
                                        circuit design. Thanks Wilf.

                                        Have fun, Duane

                                        --
                                             Home of the $35 LED solar tracker.
                                            http://www.redrok.com/electron.htm#led3
                                           CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                          Powered by\    \ \     \      \ \\   \      \      [*]
                                        Thermonuclear    \ \Solar\Energy\from the Sun \ /////|
                                        Energy(the Sun)    \ \     \      \ \\   \ / / /\/ / /|
                                                       \    \ \     \      \ /\ / \/  /  /  / |
                                           WA0VBE       \    \ \     \ /   /\ \/   /   /  \/ /|
                                          Ziggy          \    \ \/    /    / \ \/   \/    /\  |
                                                          \ /  \ \/    /     /\ \\ / \   /  / |
                                        "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                        Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                        1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                        White Bear Lake, Minnesota                \ \     /   |
                                        USA         55110-3364                     \ \        |
                                        (651)635-5O65    work                       \ \  /    |
                                        (651)426-4766   home  use Courier New Font   \ \      |
                                        (413)556-659O  Fax                copyright   \ /     |
                                        (651)583-2O62 Red Rock Energy Site (C)980907  ===\    |
                                        redrok@...     (my primary email: address) \   |
                                        redrok2@...              (Hotmail address) \  |
                                        duane.johnson@...          (Unisys  address) \ |
                                        http://www.redrok.com/index.htm    (My New Web site) \|
                                        These are my opinions, and not that of Unisys Corp.  ===

                                        To unsubscribe from this group, send an email to:
                                        beam-unsubscribe@egroups.com



                                        Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
                                      • Duane C. Johnson
                                        Hi All; I find that input protection resisters are required for safety of the inputs in AC gates. The spec limits the input or out protection diodes to 20mA.
                                        Message 19 of 27 , Nov 10, 2002
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                                          Hi All;

                                          I find that input protection resisters are required for safety of the inputs
                                          in AC gates.
                                          The spec limits the input or out protection diodes to 20mA.
                                          The outputs can drive several hundred mAs. Clearly this can
                                          damage the inputs with current fed back through the capacitors.

                                          The protection resistors weren't as important with the lower
                                          powered CMOS families.

                                          The minimum resistance is, in this case, based on VCC and
                                          the worst case threshold votage.
                                          ( VCC - 30% * VCC ) / 20mA = R
                                          ( 7V - 30% * 7V ) / 20mA = 245 ohms

                                          Prudent design calls for a minimum of about 10K.

                                          BTW, this is not just academic. I did blow of a couple of AC ICs
                                          because of this. Remember these are powerful chips.
                                           


                                          http://www.redrok.com/images/beamstepper7f.gif

                                          Neat! Now there are about 5 distinct variations of this basic design.

                                          Duane

                                          Wilf Rigter wrote:

                                          Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.---- Original Message -----
                                          Sent: Saturday, November 09, 2002 9:08 AM
                                          Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                                           Hi All;

                                          Wilf and I have been developing another solar tracker
                                          that is based on a 74AC240 Dual Quad Tristate Buffer.
                                          There have been a number of variations. This is
                                          the results. See:
                                          http://www.redrok.com/images/beamstepper7e.gif

                                          The 74AC240 stepper driver works by enabling each half
                                          of the buffer. Only one half can be enabled at a time.

                                          Let's assume that the top half of the driver is enabled.
                                          U1A & U1B along with R8, C1, & the input protection
                                          resister R7 form a square wave oscillator. The outputs
                                          of U1A & U1B directly drive one coil of a bipolar stepper
                                          motor.

                                          U1C & U1D along with R9, C2, & the input protection
                                          resister R10 form a 90 degree phase shift. The outputs
                                          of U1C & U1D directly drive the other coil of the bipolar
                                          stepper motor. The motor turns in one direction.

                                          If the second bottom half of the driver is enabled the
                                          oscillator using U1E & U1F work as before. U1H & U1G
                                          along with R12, C3, & the input protection
                                          resister R11 form a 90 degree phase shift. Except it's
                                          connected the other way around from before so it's
                                          actually 270 degrees. The outputs of U1H & U1G directly
                                          drive the other coil of the bipolar stepper motor. The
                                          motor turns in the other direction. Neat, Huh!

                                          An earlier version of the circuit didn't work well
                                          because the the sensors presented an analog enable
                                          signal. This was sometimes at the threshold voltage
                                          which caused the buffer to have high idle current and
                                          sometimes cross coupling which was a bad thing. %^(

                                          What was needed was a sensor that had a Schmitt trigger
                                          input. This could be done using a Schmitt trigger gate
                                          which works well. I suggest a 40106 or 74AHCT14. However,
                                          this needs a second IC.

                                          A better solution is to make the sensor have Schmitt
                                          action. The first version was:
                                          http://www.redrok.com/images/beamstepper7a.gif
                                          The problem was that it worked over a limited voltage
                                          range.

                                          http://www.redrok.com/images/beamstepper7e.gif
                                          works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                          latch similar in operation to an SCR.

                                          Let's start with the left side without the LEDs.
                                          Initially no current flows. The series resisters
                                          R5 & R2 cause a small bias current to flow in the base
                                          of Q1. Which pass current through R1 causing Q3 to
                                          conduct. Since Q3 shorts out R5 the current through
                                          R2 doubles. The output at the collector of Q1 snaps
                                          high disabling the connected buffer.

                                          (Note, R5 & R6 aren't actually required. It turns
                                          out that leakage currents in the transistors is enough
                                          to get started. I tried many transistors and never found
                                          one that didn't work as expected. Prudent circuit design
                                          demands that R5 & R6 be included because one might find
                                          a transistor that is so perfect it won't work. Bummer. )

                                          The now connected and lit LED1 has the ability to
                                          absorb the current through R2 starving Q1 which
                                          switches off resulting in the output snapping low.
                                          Q3 also switches off reducing the bias current
                                          in R2 to 1/2. This condition persists until the
                                          LED goes dark.

                                          You might ask where the current for the other side of
                                          the LED comes from. It is from base of Q2 on the right
                                          side. Actually, when the left side is turned off the
                                          right side is turned on doubly as the current from
                                          both R2 and R3 go through the base.

                                          The right side works the same way. Since the LEDs
                                          are connected anti parallel only one latch can
                                          be off at a time. This is safe for the buffers.

                                          When both of the quad buffers are supposed to be off
                                          it is essential that all inputs not be near the
                                          threshold to have the lowest idle current. R13 & R14
                                          ensure that all inputs be near ground. All inputs
                                          are connected to R13 or R14 either directly, through
                                          input resisters, or through the stepper motor. I
                                          added R15 & R16 for testing when the stepper motor
                                          is disconnected. If the motor is permanently
                                          connected R15 & R16 aren't needed. R13 & R14 can also
                                          be connected to VCC. They don't even need to be to
                                          the same voltage, although it operates quicker if
                                          they are the same.

                                          I have tested this circuit with about 25 different
                                          74AC240s. They all worked as expected.

                                          I ran the circuit from about 2.4V to 8.5V.
                                          OK, one shouldn't go past 7V to be within the specs
                                          of the 74AC240.

                                          The sensor section was tested to 40V. It still works
                                          well, the sensitivity is less because the bias current
                                          is proportional to voltage which requires brighter
                                          illumination to work.

                                          The step patterns are not perfectly symmetrical because
                                          this is essentially an analog circuit. Some resister
                                          adjustment can be done.

                                          To change the speed of the motor adjust the capacitor
                                          values. Note, all three need to be the same value.

                                          I have chosen the time constants of R9-C2 & R12-C3
                                          to be about 3/4ths of R8-C1. Try to keep these ratios.
                                          ( BTW, I'm not sure this is the exact ratio but it
                                          seams about right. )

                                          The 10M resisters in the sensor are the largest
                                          commonly available resisters in 1/8W size. I tried
                                          22M in 1/4W and that worked well with added
                                          sensitivity. I suppose if you could find 100M they
                                          would work even better.

                                          I have a variation which is even more sensitive to
                                          low light levels. Ask me if you want this variation.

                                          I have to thank Wilf for his invaluable help in the
                                          circuit design. Thanks Wilf.

                                          Have fun, Duane

                                          --
                                               Home of the $35 LED solar tracker.
                                              http://www.redrok.com/electron.htm#led3
                                             CUL8ER  \    \ \     \      \ \\   \      \  Receiver
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                                             CUL8ER  \    \ \     \      \ \\   \      \  Receiver
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                                          "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                          Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                          1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                          White Bear Lake, Minnesota                \ \     /   |
                                          USA         55110-3364                     \ \        |
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                                          These are my opinions, and not that of Unisys Corp.  ===
                                           
                                        • Scott Burns
                                          I was under the impression that CMOS inputs were high resistance and that very little current passed through. (?) Scott
                                          Message 20 of 27 , Nov 10, 2002
                                          View Source
                                          • 0 Attachment
                                            I was under the impression that CMOS inputs were high resistance and that very little current passed through. (?)

                                            Scott

                                            At 09:30 AM 11/10/2002 -0600, you wrote:
                                            Hi All;

                                            I find that input protection resisters are required for safety of the
                                            inputs
                                            in AC gates.
                                            The spec limits the input or out protection diodes to 20mA.
                                            The outputs can drive several hundred mAs. Clearly this can
                                            damage the inputs with current fed back through the capacitors.

                                            The protection resistors weren't as important with the lower
                                            powered CMOS families.

                                            The minimum resistance is, in this case, based on VCC and
                                            the worst case threshold votage.
                                            ( VCC - 30% * VCC ) / 20mA = R
                                            ( 7V - 30% * 7V ) / 20mA = 245 ohms

                                            Prudent design calls for a minimum of about 10K.

                                            BTW, this is not just academic. I did blow of a couple of AC ICs
                                            because of this. Remember these are powerful chips.


                                            [Image]
                                            http://www.redrok.com/images/beamstepper7f.gif

                                            Neat! Now there are about 5 distinct variations of this basic design.

                                            Duane

                                            Wilf Rigter wrote:

                                            > Here is yet another variation of the stepper circuit, somewhat easier
                                            > to read and clearly shows the master slave monocore topology. Note
                                            > that in this case the resistors for the slave monocores are connected
                                            > to the complementary outputs of the master monocore.  ---- Original
                                            > Message -----
                                            >
                                            >      From:Duane C. Johnson
                                            >      To: beam@yahoogroups.com
                                            >      Cc: wilf_nv
                                            >      Sent: Saturday, November 09, 2002 9:08 AM
                                            >      Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                                            >       Hi All;
                                            >
                                            >      Wilf and I have been developing another solar tracker
                                            >      that is based on a 74AC240 Dual Quad Tristate Buffer.
                                            >      There have been a number of variations. This is
                                            >      the results. See:
                                            >      http://www.redrok.com/images/beamstepper7e.gif
                                            >
                                            >      The 74AC240 stepper driver works by enabling each half
                                            >      of the buffer. Only one half can be enabled at a time.
                                            >
                                            >      Let's assume that the top half of the driver is enabled.
                                            >      U1A & U1B along with R8, C1, & the input protection
                                            >      resister R7 form a square wave oscillator. The outputs
                                            >      of U1A & U1B directly drive one coil of a bipolar stepper
                                            >      motor.
                                            >
                                            >      U1C & U1D along with R9, C2, & the input protection
                                            >      resister R10 form a 90 degree phase shift. The outputs
                                            >      of U1C & U1D directly drive the other coil of the bipolar
                                            >      stepper motor. The motor turns in one direction.
                                            >
                                            >      If the second bottom half of the driver is enabled the
                                            >      oscillator using U1E & U1F work as before. U1H & U1G
                                            >      along with R12, C3, & the input protection
                                            >      resister R11 form a 90 degree phase shift. Except it's
                                            >      connected the other way around from before so it's
                                            >      actually 270 degrees. The outputs of U1H & U1G directly
                                            >      drive the other coil of the bipolar stepper motor. The
                                            >      motor turns in the other direction. Neat, Huh!
                                            >
                                            >      An earlier version of the circuit didn't work well
                                            >      because the the sensors presented an analog enable
                                            >      signal. This was sometimes at the threshold voltage
                                            >      which caused the buffer to have high idle current and
                                            >      sometimes cross coupling which was a bad thing. %^(
                                            >
                                            >      What was needed was a sensor that had a Schmitt trigger
                                            >      input. This could be done using a Schmitt trigger gate
                                            >      which works well. I suggest a 40106 or 74AHCT14. However,
                                            >      this needs a second IC.
                                            >
                                            >      A better solution is to make the sensor have Schmitt
                                            >      action. The first version was:
                                            >      http://www.redrok.com/images/beamstepper7a.gif
                                            >      The problem was that it worked over a limited voltage
                                            >      range.
                                            >
                                            >      http://www.redrok.com/images/beamstepper7e.gif
                                            >      works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                            >      latch similar in operation to an SCR.
                                            >
                                            >      Let's start with the left side without the LEDs.
                                            >      Initially no current flows. The series resisters
                                            >      R5 & R2 cause a small bias current to flow in the base
                                            >      of Q1. Which pass current through R1 causing Q3 to
                                            >      conduct. Since Q3 shorts out R5 the current through
                                            >      R2 doubles. The output at the collector of Q1 snaps
                                            >      high disabling the connected buffer.
                                            >
                                            >      (Note, R5 & R6 aren't actually required. It turns
                                            >      out that leakage currents in the transistors is enough
                                            >      to get started. I tried many transistors and never found
                                            >      one that didn't work as expected. Prudent circuit design
                                            >      demands that R5 & R6 be included because one might find
                                            >      a transistor that is so perfect it won't work. Bummer. )
                                            >
                                            >      The now connected and lit LED1 has the ability to
                                            >      absorb the current through R2 starving Q1 which
                                            >      switches off resulting in the output snapping low.
                                            >      Q3 also switches off reducing the bias current
                                            >      in R2 to 1/2. This condition persists until the
                                            >      LED goes dark.
                                            >
                                            >      You might ask where the current for the other side of
                                            >      the LED comes from. It is from base of Q2 on the right
                                            >      side. Actually, when the left side is turned off the
                                            >      right side is turned on doubly as the current from
                                            >      both R2 and R3 go through the base.
                                            >
                                            >      The right side works the same way. Since the LEDs
                                            >      are connected anti parallel only one latch can
                                            >      be off at a time. This is safe for the buffers.
                                            >
                                            >      When both of the quad buffers are supposed to be off
                                            >      it is essential that all inputs not be near the
                                            >      threshold to have the lowest idle current. R13 & R14
                                            >      ensure that all inputs be near ground. All inputs
                                            >      are connected to R13 or R14 either directly, through
                                            >      input resisters, or through the stepper motor. I
                                            >      added R15 & R16 for testing when the stepper motor
                                            >      is disconnected. If the motor is permanently
                                            >      connected R15 & R16 aren't needed. R13 & R14 can also
                                            >      be connected to VCC. They don't even need to be to
                                            >      the same voltage, although it operates quicker if
                                            >      they are the same.
                                            >
                                            >      I have tested this circuit with about 25 different
                                            >      74AC240s. They all worked as expected.
                                            >
                                            >      I ran the circuit from about 2.4V to 8.5V.
                                            >      OK, one shouldn't go past 7V to be within the specs
                                            >      of the 74AC240.
                                            >
                                            >      The sensor section was tested to 40V. It still works
                                            >      well, the sensitivity is less because the bias current
                                            >      is proportional to voltage which requires brighter
                                            >      illumination to work.
                                            >
                                            >      The step patterns are not perfectly symmetrical because
                                            >      this is essentially an analog circuit. Some resister
                                            >      adjustment can be done.
                                            >
                                            >      To change the speed of the motor adjust the capacitor
                                            >      values. Note, all three need to be the same value.
                                            >
                                            >      I have chosen the time constants of R9-C2 & R12-C3
                                            >      to be about 3/4ths of R8-C1. Try to keep these ratios.
                                            >      ( BTW, I'm not sure this is the exact ratio but it
                                            >      seams about right. )
                                            >
                                            >      The 10M resisters in the sensor are the largest
                                            >      commonly available resisters in 1/8W size. I tried
                                            >      22M in 1/4W and that worked well with added
                                            >      sensitivity. I suppose if you could find 100M they
                                            >      would work even better.
                                            >
                                            >      I have a variation which is even more sensitive to
                                            >      low light levels. Ask me if you want this variation.
                                            >
                                            >      I have to thank Wilf for his invaluable help in the
                                            >      circuit design. Thanks Wilf.
                                            >
                                            >      Have fun, Duane
                                            >
                                            >      --
                                            >           Home of the $35 LED solar tracker.
                                            >          http://www.redrok.com/electron.htm#led3
                                            >         CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                            >        Powered by\    \ \     \      \ \\   \      \      [*]
                                            >      Thermonuclear    \ \Solar\Energy\from the Sun \ /////|
                                            >      Energy(the Sun)    \ \     \      \ \\   \ / / /\/ / /|
                                            >                     \    \ \     \      \ /\ / \/  /  /  / |
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                                            >      "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                            >      Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                            >      1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                            >      White Bear Lake, Minnesota                \ \     /   |
                                            >      USA         55110-3364                     \ \        |
                                            >      (651)635-5O65    work                       \ \  /    |
                                            >      (651)426-4766   home  use Courier New Font   \ \      |
                                            >      (413)556-659O  Fax                copyright   \ /     |
                                            >      (651)583-2O62 Red Rock Energy Site (C)980907  ===\    |
                                            >      redrok@...     (my primary email: address) \   |
                                            >      redrok2@...              (Hotmail address) \  |
                                            >      duane.johnson@...          (Unisys  address) \ |
                                            >      http://www.redrok.com/index.htm   (My New Web site) \|
                                            >      These are my opinions, and not that of Unisys Corp.  ===
                                            >
                                            >      To unsubscribe from this group, send an email to:
                                            >      beam-unsubscribe@egroups.com
                                            >
                                            >
                                            >
                                            >      Your use of Yahoo! Groups is subject to the Yahoo! Terms of
                                            >      Service.
                                            >
                                            >
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                                            >
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                                            --
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                                               CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                              Powered by\    \ \     \      \ \\   \      \      [*]
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                                            "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                            Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                            1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                            White Bear Lake, Minnesota                \ \     /   |
                                            USA         55110-3364                     \ \        |
                                            (651)635-5O65    work                       \ \  /    |
                                            (651)426-4766   home  use Courier New Font   \ \      |
                                            (413)556-659O  Fax                copyright   \ /     |
                                            (651)583-2O62 Red Rock Energy Site (C)980907  ===\    |
                                            redrok@...     (my primary email: address) \   |
                                            redrok2@...              (Hotmail address) \  |
                                            duane.johnson@...          (Unisys  address) \ |
                                            http://www.redrok.com/index.htm   (My New Web site) \|
                                            These are my opinions, and not that of Unisys Corp.  ===

                                            Hi All;

                                            I find that input protection resisters are required for safety of the inputs
                                            in AC gates.
                                            The spec limits the input or out protection diodes to 20mA.
                                            The outputs can drive several hundred mAs. Clearly this can
                                            damage the inputs with current fed back through the capacitors.

                                            The protection resistors weren't as important with the lower
                                            powered CMOS families.

                                            The minimum resistance is, in this case, based on VCC and
                                            the worst case threshold votage.
                                            ( VCC - 30% * VCC ) / 20mA = R
                                            ( 7V - 30% * 7V ) / 20mA = 245 ohms

                                            Prudent design calls for a minimum of about 10K.

                                            BTW, this is not just academic. I did blow of a couple of AC ICs
                                            because of this. Remember these are powerful chips.
                                             

                                            CWINDOWSTEMPnsmail32.jpg 
                                            http://www.redrok.com/images/beamstepper7f.gif

                                            Neat! Now there are about 5 distinct variations of this basic design.

                                            Duane

                                            Wilf Rigter wrote:
                                            Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.beamstepper7f1.gif---- Original Message -----
                                            From:Duane C. Johnson
                                            To: beam@yahoogroups.com
                                            Cc: wilf_nv
                                            Sent: Saturday, November 09, 2002 9:08 AM
                                            Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                                             Hi All;

                                            Wilf and I have been developing another solar tracker
                                            that is based on a 74AC240 Dual Quad Tristate Buffer.
                                            There have been a number of variations. This is
                                            the results. See:
                                            http://www.redrok.com/images/beamstepper7e.gif


                                            The 74AC240 stepper driver works by enabling each half
                                            of the buffer. Only one half can be enabled at a time.


                                            Let's assume that the top half of the driver is enabled.
                                            U1A & U1B along with R8, C1, & the input protection
                                            resister R7 form a square wave oscillator. The outputs
                                            of U1A & U1B directly drive one coil of a bipolar stepper
                                            motor.


                                            U1C & U1D along with R9, C2, & the input protection
                                            resister R10 form a 90 degree phase shift. The outputs
                                            of U1C & U1D directly drive the other coil of the bipolar
                                            stepper motor. The motor turns in one direction.


                                            If the second bottom half of the driver is enabled the
                                            oscillator using U1E & U1F work as before. U1H & U1G
                                            along with R12, C3, & the input protection
                                            resister R11 form a 90 degree phase shift. Except it's
                                            connected the other way around from before so it's
                                            actually 270 degrees. The outputs of U1H & U1G directly
                                            drive the other coil of the bipolar stepper motor. The
                                            motor turns in the other direction. Neat, Huh!


                                            An earlier version of the circuit didn't work well
                                            because the the sensors presented an analog enable
                                            signal. This was sometimes at the threshold voltage
                                            which caused the buffer to have high idle current and
                                            sometimes cross coupling which was a bad thing. %^(


                                            What was needed was a sensor that had a Schmitt trigger
                                            input. This could be done using a Schmitt trigger gate
                                            which works well. I suggest a 40106 or 74AHCT14. However,
                                            this needs a second IC.


                                            A better solution is to make the sensor have Schmitt
                                            action. The first version was:
                                            http://www.redrok.com/images/beamstepper7a.gif
                                            The problem was that it worked over a limited voltage
                                            range.


                                            http://www.redrok.com/images/beamstepper7e.gif
                                            works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                            latch similar in operation to an SCR.


                                            Let's start with the left side without the LEDs.
                                            Initially no current flows. The series resisters
                                            R5 & R2 cause a small bias current to flow in the base
                                            of Q1. Which pass current through R1 causing Q3 to
                                            conduct. Since Q3 shorts out R5 the current through
                                            R2 doubles. The output at the collector of Q1 snaps
                                            high disabling the connected buffer.


                                            (Note, R5 & R6 aren't actually required. It turns
                                            out that leakage currents in the transistors is enough
                                            to get started. I tried many transistors and never found
                                            one that didn't work as expected. Prudent circuit design
                                            demands that R5 & R6 be included because one might find
                                            a transistor that is so perfect it won't work. Bummer. )


                                            The now connected and lit LED1 has the ability to
                                            absorb the current through R2 starving Q1 which
                                            switches off resulting in the output snapping low.
                                            Q3 also switches off reducing the bias current
                                            in R2 to 1/2. This condition persists until the
                                            LED goes dark.


                                            You might ask where the current for the other side of
                                            the LED comes from. It is from base of Q2 on the right
                                            side. Actually, when the left side is turned off the
                                            right side is turned on doubly as the current from
                                            both R2 and R3 go through the base.


                                            The right side works the same way. Since the LEDs
                                            are connected anti parallel only one latch can
                                            be off at a time. This is safe for the buffers.


                                            When both of the quad buffers are supposed to be off
                                            it is essential that all inputs not be near the
                                            threshold to have the lowest idle current. R13 & R14
                                            ensure that all inputs be near ground. All inputs
                                            are connected to R13 or R14 either directly, through
                                            input resisters, or through the stepper motor. I
                                            added R15 & R16 for testing when the stepper motor
                                            is disconnected. If the motor is permanently
                                            connected R15 & R16 aren't needed. R13 & R14 can also
                                            be connected to VCC. They don't even need to be to
                                            the same voltage, although it operates quicker if
                                            they are the same.


                                            I have tested this circuit with about 25 different
                                            74AC240s. They all worked as expected.


                                            I ran the circuit from about 2.4V to 8.5V.
                                            OK, one shouldn't go past 7V to be within the specs
                                            of the 74AC240.


                                            The sensor section was tested to 40V. It still works
                                            well, the sensitivity is less because the bias current
                                            is proportional to voltage which requires brighter
                                            illumination to work.


                                            The step patterns are not perfectly symmetrical because
                                            this is essentially an analog circuit. Some resister
                                            adjustment can be done.


                                            To change the speed of the motor adjust the capacitor
                                            values. Note, all three need to be the same value.


                                            I have chosen the time constants of R9-C2 & R12-C3
                                            to be about 3/4ths of R8-C1. Try to keep these ratios.
                                            ( BTW, I'm not sure this is the exact ratio but it
                                            seams about right. )


                                            The 10M resisters in the sensor are the largest
                                            commonly available resisters in 1/8W size. I tried
                                            22M in 1/4W and that worked well with added
                                            sensitivity. I suppose if you could find 100M they
                                            would work even better.


                                            I have a variation which is even more sensitive to
                                            low light levels. Ask me if you want this variation.


                                            I have to thank Wilf for his invaluable help in the
                                            circuit design. Thanks Wilf.


                                            Have fun, Duane


                                            --
                                                 Home of the $35 LED solar tracker.
                                                http://www.redrok.com/electron.htm#led3
                                               CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                              Powered by\    \ \     \      \ \\   \      \      [*]
                                            Thermonuclear    \ \Solar\Energy\from the Sun \ /////|
                                            Energy(the Sun)    \ \     \      \ \\   \ / / /\/ / /|
                                                           \    \ \     \      \ /\ / \/  /  /  / |
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                                          • Duane C. Johnson
                                            Hi Scott; ... Yes and no. The input us very high impedance when kept between ground and VCC. Outside of this range protection diodes are used to shunt current
                                            Message 21 of 27 , Nov 10, 2002
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                                              Hi Scott;

                                              Scott Burns wrote:

                                              > I was under the impression that CMOS inputs were high
                                              > resistance and that very little current passed through. (?)

                                              Yes and no. The input us very high impedance when
                                              kept between ground and VCC. Outside of this range
                                              protection diodes are used to shunt current to the
                                              power rails to protect the MOS gates from over voltage.

                                              Here is the spec for the 74AC240
                                              http://www.solarbotics.net/library/datasheets/74AC240.pdf

                                              > Scott

                                              Duane

                                              > At 09:30 AM 11/10/2002 -0600, you wrote:

                                              > > I find that input protection resisters are required
                                              > > for safety of the inputs in AC gates. The spec limits
                                              > > the input or out protection diodes to 20mA. The
                                              > > outputs can drive several hundred mAs. Clearly this
                                              > > can damage the inputs with current fed back through
                                              > > the capacitors.

                                              > > Prudent design calls for a minimum of about 10K.

                                              > > http://www.redrok.com/images/beamstepper7f.gif

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                                            • Wilf Rigter
                                              Hello Duane et al, The input resistors and actual component values were omitted for clarity and to show the similarity to monocore circuit. The modfied circuit
                                              Message 22 of 27 , Nov 10, 2002
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                                                Hello Duane et al,
                                                 
                                                The input resistors and actual component values were omitted for clarity and to show the similarity to monocore circuit. The modfied circuit using the input resistors and the same component values as the original is shown here inline or attached:
                                                 
                                                 
                                                When 74HC or AC devices used in applications as relaxation oscillators, the external input resistors are often omitted by design and the input diodes are intentionally used to clamp the input voltage of the timing capacitor. 
                                                 
                                                The literature specifies 20ma as the absolute maximum clamping current. While I cannot recommend  exceeding this, 20ma  is quite conservative and higher peak input currents are usually tolerated.    
                                                 
                                                 
                                                Oscillators or networks using 74HC/AC parts in quasi-linear applications, like the microcore and bicore, use capacitive coupling. The switching of partially charged capacitors generates potential overvoltages in excess of Vcc/2 at the inputs. If no external series input resistor the transient at the input will be current limited by the internal 100 ohm series polysilicon resistor and will be voltage limited by driver output voltage drop in series with the input internal resistor  and the dynamic impedance of the clamping diodes. For Vcc= 5V  the transient potential overvoltage is 2.5V and the combined internal output and input resistance plus the diode drop would limit the current to less than 20ma even if no external input resistor is used.
                                                 
                                                However, there are other good reasons to include the series resistor related to frequency and dutycyle stability. Applications notes often suggest using a series resistor value of 10x the feedback resistor value to avoid clamping the AC coupled feedback signal. Not calmping the feedback signal effectively increases the RC time constant, decreases power consumption and, importantly, averages the DC level at the input near the threshold.  The latter tends to move the dutycyle of the oscilator automatically toward a symmetrical waveform.  One of my earliest posts to this list described an using series input resistors in an article called Belted and Suspended Bicores including a  method to control of the average dc voltage at the input which can be used to adjust the dutycycle.
                                                 
                                                To complicate matters a little bit, the Beamish Stepper Motor circuit outputs directly drive the stepper coils. The inductive load generates its own transients at the outputs which may exceed the output diode ratings Moreover motor loading of the output causes a voltage drop which together with  switching transients can be coupled back through the feedback capacitor to the inputs and can cause timing instability.  This motor load volatge drop is proportional to motor current and can be put to some good use in other applications to truncate the oscillator cycle and reverse a heavily overloaded motor.  For some applications it is desirable to control the duty cycle of a slave bicore (e.g. turning in a bicore walker by injecting a dc current into the input node) but the averaging effect of adding series input resistors would oppose the dc control signal and must be taken into account in such a design. 
                                                 
                                                Now a question on the Beamish Stepper Motor Circuit: Since the values of the series input resistors are the same order of magnitude as the RC timing  resistors and their effect on the time constant can not be ignored,  I am curious how you decided on using those particular values. 
                                                 
                                                best regard
                                                 
                                                wilf
                                                ----- Original Message -----
                                                Sent: Sunday, November 10, 2002 7:30 AM
                                                Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                                Hi All;

                                                I find that input protection resisters are required for safety of the inputs
                                                in AC gates.
                                                The spec limits the input or out protection diodes to 20mA.
                                                The outputs can drive several hundred mAs. Clearly this can
                                                damage the inputs with current fed back through the capacitors.

                                                The protection resistors weren't as important with the lower
                                                powered CMOS families.

                                                The minimum resistance is, in this case, based on VCC and
                                                the worst case threshold votage.
                                                ( VCC - 30% * VCC ) / 20mA = R
                                                ( 7V - 30% * 7V ) / 20mA = 245 ohms

                                                Prudent design calls for a minimum of about 10K.

                                                BTW, this is not just academic. I did blow of a couple of AC ICs
                                                because of this. Remember these are powerful chips.
                                                 


                                                http://www.redrok.com/images/beamstepper7f.gif

                                                Neat! Now there are about 5 distinct variations of this basic design.

                                                Duane

                                                Wilf Rigter wrote:

                                                Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.---- Original Message -----
                                                Sent: Saturday, November 09, 2002 9:08 AM
                                                Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                                                 Hi All;

                                                Wilf and I have been developing another solar tracker
                                                that is based on a 74AC240 Dual Quad Tristate Buffer.
                                                There have been a number of variations. This is
                                                the results. See:
                                                http://www.redrok.com/images/beamstepper7e.gif

                                                The 74AC240 stepper driver works by enabling each half
                                                of the buffer. Only one half can be enabled at a time.

                                                Let's assume that the top half of the driver is enabled.
                                                U1A & U1B along with R8, C1, & the input protection
                                                resister R7 form a square wave oscillator. The outputs
                                                of U1A & U1B directly drive one coil of a bipolar stepper
                                                motor.

                                                U1C & U1D along with R9, C2, & the input protection
                                                resister R10 form a 90 degree phase shift. The outputs
                                                of U1C & U1D directly drive the other coil of the bipolar
                                                stepper motor. The motor turns in one direction.

                                                If the second bottom half of the driver is enabled the
                                                oscillator using U1E & U1F work as before. U1H & U1G
                                                along with R12, C3, & the input protection
                                                resister R11 form a 90 degree phase shift. Except it's
                                                connected the other way around from before so it's
                                                actually 270 degrees. The outputs of U1H & U1G directly
                                                drive the other coil of the bipolar stepper motor. The
                                                motor turns in the other direction. Neat, Huh!

                                                An earlier version of the circuit didn't work well
                                                because the the sensors presented an analog enable
                                                signal. This was sometimes at the threshold voltage
                                                which caused the buffer to have high idle current and
                                                sometimes cross coupling which was a bad thing. %^(

                                                What was needed was a sensor that had a Schmitt trigger
                                                input. This could be done using a Schmitt trigger gate
                                                which works well. I suggest a 40106 or 74AHCT14. However,
                                                this needs a second IC.

                                                A better solution is to make the sensor have Schmitt
                                                action. The first version was:
                                                http://www.redrok.com/images/beamstepper7a.gif
                                                The problem was that it worked over a limited voltage
                                                range.

                                                http://www.redrok.com/images/beamstepper7e.gif
                                                works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                                latch similar in operation to an SCR.

                                                Let's start with the left side without the LEDs.
                                                Initially no current flows. The series resisters
                                                R5 & R2 cause a small bias current to flow in the base
                                                of Q1. Which pass current through R1 causing Q3 to
                                                conduct. Since Q3 shorts out R5 the current through
                                                R2 doubles. The output at the collector of Q1 snaps
                                                high disabling the connected buffer.

                                                (Note, R5 & R6 aren't actually required. It turns
                                                out that leakage currents in the transistors is enough
                                                to get started. I tried many transistors and never found
                                                one that didn't work as expected. Prudent circuit design
                                                demands that R5 & R6 be included because one might find
                                                a transistor that is so perfect it won't work. Bummer. )

                                                The now connected and lit LED1 has the ability to
                                                absorb the current through R2 starving Q1 which
                                                switches off resulting in the output snapping low.
                                                Q3 also switches off reducing the bias current
                                                in R2 to 1/2. This condition persists until the
                                                LED goes dark.

                                                You might ask where the current for the other side of
                                                the LED comes from. It is from base of Q2 on the right
                                                side. Actually, when the left side is turned off the
                                                right side is turned on doubly as the current from
                                                both R2 and R3 go through the base.

                                                The right side works the same way. Since the LEDs
                                                are connected anti parallel only one latch can
                                                be off at a time. This is safe for the buffers.

                                                When both of the quad buffers are supposed to be off
                                                it is essential that all inputs not be near the
                                                threshold to have the lowest idle current. R13 & R14
                                                ensure that all inputs be near ground. All inputs
                                                are connected to R13 or R14 either directly, through
                                                input resisters, or through the stepper motor. I
                                                added R15 & R16 for testing when the stepper motor
                                                is disconnected. If the motor is permanently
                                                connected R15 & R16 aren't needed. R13 & R14 can also
                                                be connected to VCC. They don't even need to be to
                                                the same voltage, although it operates quicker if
                                                they are the same.

                                                I have tested this circuit with about 25 different
                                                74AC240s. They all worked as expected.

                                                I ran the circuit from about 2.4V to 8.5V.
                                                OK, one shouldn't go past 7V to be within the specs
                                                of the 74AC240.

                                                The sensor section was tested to 40V. It still works
                                                well, the sensitivity is less because the bias current
                                                is proportional to voltage which requires brighter
                                                illumination to work.

                                                The step patterns are not perfectly symmetrical because
                                                this is essentially an analog circuit. Some resister
                                                adjustment can be done.

                                                To change the speed of the motor adjust the capacitor
                                                values. Note, all three need to be the same value.

                                                I have chosen the time constants of R9-C2 & R12-C3
                                                to be about 3/4ths of R8-C1. Try to keep these ratios.
                                                ( BTW, I'm not sure this is the exact ratio but it
                                                seams about right. )

                                                The 10M resisters in the sensor are the largest
                                                commonly available resisters in 1/8W size. I tried
                                                22M in 1/4W and that worked well with added
                                                sensitivity. I suppose if you could find 100M they
                                                would work even better.

                                                I have a variation which is even more sensitive to
                                                low light levels. Ask me if you want this variation.

                                                I have to thank Wilf for his invaluable help in the
                                                circuit design. Thanks Wilf.

                                                Have fun, Duane

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                                                "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                                Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                                1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                                White Bear Lake, Minnesota                \ \     /   |
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                                                (413)556-659O  Fax                copyright   \ /     |
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                                              • Jérôme Demers
                                                Hello wilf, This really clear and easy to understand. You could attach a bicore to the input of this stepper circuit to make a walker or a oscillating steper
                                                Message 23 of 27 , Nov 10, 2002
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                                                  Hello wilf,
                                                   
                                                  This really clear and easy to understand. You could attach a bicore to the input of this stepper circuit to make a walker or a oscillating steper motor.
                                                   
                                                  Really cool.
                                                   
                                                  PS-- Do I have stepper motor in my motor box? I will check it out.
                                                   
                                                  Jérôme Demers
                                                  "Insectroïdes" the next generation of insects
                                                  http://robomaniac.solarbotics.net
                                                   
                                                  ----- Original Message -----
                                                  Sent: Saturday, November 09, 2002 7:52 PM
                                                  Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                                  Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.
                                                   
                                                   
                                                  ---- Original Message -----
                                                  Sent: Saturday, November 09, 2002 9:08 AM
                                                  Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                                  Hi All;

                                                  Wilf and I have been developing another solar tracker
                                                  that is based on a 74AC240 Dual Quad Tristate Buffer.
                                                  There have been a number of variations. This is
                                                  the results. See:
                                                  http://www.redrok.com/images/beamstepper7e.gif

                                                  The 74AC240 stepper driver works by enabling each half
                                                  of the buffer. Only one half can be enabled at a time.

                                                  Let's assume that the top half of the driver is enabled.
                                                  U1A & U1B along with R8, C1, & the input protection
                                                  resister R7 form a square wave oscillator. The outputs
                                                  of U1A & U1B directly drive one coil of a bipolar stepper
                                                  motor.

                                                  U1C & U1D along with R9, C2, & the input protection
                                                  resister R10 form a 90 degree phase shift. The outputs
                                                  of U1C & U1D directly drive the other coil of the bipolar
                                                  stepper motor. The motor turns in one direction.

                                                  If the second bottom half of the driver is enabled the
                                                  oscillator using U1E & U1F work as before. U1H & U1G
                                                  along with R12, C3, & the input protection
                                                  resister R11 form a 90 degree phase shift. Except it's
                                                  connected the other way around from before so it's
                                                  actually 270 degrees. The outputs of U1H & U1G directly
                                                  drive the other coil of the bipolar stepper motor. The
                                                  motor turns in the other direction. Neat, Huh!

                                                  An earlier version of the circuit didn't work well
                                                  because the the sensors presented an analog enable
                                                  signal. This was sometimes at the threshold voltage
                                                  which caused the buffer to have high idle current and
                                                  sometimes cross coupling which was a bad thing. %^(

                                                  What was needed was a sensor that had a Schmitt trigger
                                                  input. This could be done using a Schmitt trigger gate
                                                  which works well. I suggest a 40106 or 74AHCT14. However,
                                                  this needs a second IC.

                                                  A better solution is to make the sensor have Schmitt
                                                  action. The first version was:
                                                  http://www.redrok.com/images/beamstepper7a.gif
                                                  The problem was that it worked over a limited voltage
                                                  range.

                                                  http://www.redrok.com/images/beamstepper7e.gif
                                                  works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                                  latch similar in operation to an SCR.

                                                  Let's start with the left side without the LEDs.
                                                  Initially no current flows. The series resisters
                                                  R5 & R2 cause a small bias current to flow in the base
                                                  of Q1. Which pass current through R1 causing Q3 to
                                                  conduct. Since Q3 shorts out R5 the current through
                                                  R2 doubles. The output at the collector of Q1 snaps
                                                  high disabling the connected buffer.

                                                  (Note, R5 & R6 aren't actually required. It turns
                                                  out that leakage currents in the transistors is enough
                                                  to get started. I tried many transistors and never found
                                                  one that didn't work as expected. Prudent circuit design
                                                  demands that R5 & R6 be included because one might find
                                                  a transistor that is so perfect it won't work. Bummer. )

                                                  The now connected and lit LED1 has the ability to
                                                  absorb the current through R2 starving Q1 which
                                                  switches off resulting in the output snapping low.
                                                  Q3 also switches off reducing the bias current
                                                  in R2 to 1/2. This condition persists until the
                                                  LED goes dark.

                                                  You might ask where the current for the other side of
                                                  the LED comes from. It is from base of Q2 on the right
                                                  side. Actually, when the left side is turned off the
                                                  right side is turned on doubly as the current from
                                                  both R2 and R3 go through the base.

                                                  The right side works the same way. Since the LEDs
                                                  are connected anti parallel only one latch can
                                                  be off at a time. This is safe for the buffers.

                                                  When both of the quad buffers are supposed to be off
                                                  it is essential that all inputs not be near the
                                                  threshold to have the lowest idle current. R13 & R14
                                                  ensure that all inputs be near ground. All inputs
                                                  are connected to R13 or R14 either directly, through
                                                  input resisters, or through the stepper motor. I
                                                  added R15 & R16 for testing when the stepper motor
                                                  is disconnected. If the motor is permanently
                                                  connected R15 & R16 aren't needed. R13 & R14 can also
                                                  be connected to VCC. They don't even need to be to
                                                  the same voltage, although it operates quicker if
                                                  they are the same.

                                                  I have tested this circuit with about 25 different
                                                  74AC240s. They all worked as expected.

                                                  I ran the circuit from about 2.4V to 8.5V.
                                                  OK, one shouldn't go past 7V to be within the specs
                                                  of the 74AC240.

                                                  The sensor section was tested to 40V. It still works
                                                  well, the sensitivity is less because the bias current
                                                  is proportional to voltage which requires brighter
                                                  illumination to work.

                                                  The step patterns are not perfectly symmetrical because
                                                  this is essentially an analog circuit. Some resister
                                                  adjustment can be done.

                                                  To change the speed of the motor adjust the capacitor
                                                  values. Note, all three need to be the same value.

                                                  I have chosen the time constants of R9-C2 & R12-C3
                                                  to be about 3/4ths of R8-C1. Try to keep these ratios.
                                                  ( BTW, I'm not sure this is the exact ratio but it
                                                  seams about right. )

                                                  The 10M resisters in the sensor are the largest
                                                  commonly available resisters in 1/8W size. I tried
                                                  22M in 1/4W and that worked well with added
                                                  sensitivity. I suppose if you could find 100M they
                                                  would work even better.

                                                  I have a variation which is even more sensitive to
                                                  low light levels. Ask me if you want this variation.

                                                  I have to thank Wilf for his invaluable help in the
                                                  circuit design. Thanks Wilf.

                                                  Have fun, Duane

                                                  --
                                                       Home of the $35 LED solar tracker.
                                                      http://www.redrok.com/electron.htm#led3
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                                                • Wilf Rigter
                                                  Excelent Jerome, Use two head positioning stepper motors removed from old mac floppy drives, connect the two master bicore outputs to the forward and
                                                  Message 24 of 27 , Nov 10, 2002
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                                                    Excelent Jerome,
                                                     
                                                    Use two head positioning stepper motors removed from old mac floppy drives,  connect the two master bicore outputs to the "forward" and "reverse" inputs of the front stepper motor circuit and the slave bicore outputs to the rear stepper motor circuit. and you have a two stepper walker. You will still need to use a gearbox to give the required torque.
                                                     
                                                    Alternately you can use the same stepper motor circuit, with longer time constant components, as a two motor walker controller. This controller in turn controls two identical copies of the stepper motor driver circuit. The controller circuit output connections go to the forward and reverse inputs of the two stepper motor driver circuits.
                                                    I can post a schematic if you like.
                                                     
                                                     
                                                    wilf
                                                     
                                                     
                                                     
                                                    ----- Original Message -----
                                                    Sent: Sunday, November 10, 2002 3:15 PM
                                                    Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                                    Hello wilf,
                                                     
                                                    This really clear and easy to understand. You could attach a bicore to the input of this stepper circuit to make a walker or a oscillating steper motor.
                                                     
                                                    Really cool.
                                                     
                                                    PS-- Do I have stepper motor in my motor box? I will check it out.
                                                     
                                                    Jérôme Demers
                                                    "Insectroïdes" the next generation of insects
                                                    http://robomaniac.solarbotics.net
                                                     
                                                    ----- Original Message -----
                                                    Sent: Saturday, November 09, 2002 7:52 PM
                                                    Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                                    Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.
                                                     
                                                     
                                                    ---- Original Message -----
                                                    Sent: Saturday, November 09, 2002 9:08 AM
                                                    Subject: Re: [beam] Re: Beamish Stepper Motor Driver

                                                    Hi All;

                                                    Wilf and I have been developing another solar tracker
                                                    that is based on a 74AC240 Dual Quad Tristate Buffer.
                                                    There have been a number of variations. This is
                                                    the results. See:
                                                    http://www.redrok.com/images/beamstepper7e.gif

                                                    The 74AC240 stepper driver works by enabling each half
                                                    of the buffer. Only one half can be enabled at a time.

                                                    Let's assume that the top half of the driver is enabled.
                                                    U1A & U1B along with R8, C1, & the input protection
                                                    resister R7 form a square wave oscillator. The outputs
                                                    of U1A & U1B directly drive one coil of a bipolar stepper
                                                    motor.

                                                    U1C & U1D along with R9, C2, & the input protection
                                                    resister R10 form a 90 degree phase shift. The outputs
                                                    of U1C & U1D directly drive the other coil of the bipolar
                                                    stepper motor. The motor turns in one direction.

                                                    If the second bottom half of the driver is enabled the
                                                    oscillator using U1E & U1F work as before. U1H & U1G
                                                    along with R12, C3, & the input protection
                                                    resister R11 form a 90 degree phase shift. Except it's
                                                    connected the other way around from before so it's
                                                    actually 270 degrees. The outputs of U1H & U1G directly
                                                    drive the other coil of the bipolar stepper motor. The
                                                    motor turns in the other direction. Neat, Huh!

                                                    An earlier version of the circuit didn't work well
                                                    because the the sensors presented an analog enable
                                                    signal. This was sometimes at the threshold voltage
                                                    which caused the buffer to have high idle current and
                                                    sometimes cross coupling which was a bad thing. %^(

                                                    What was needed was a sensor that had a Schmitt trigger
                                                    input. This could be done using a Schmitt trigger gate
                                                    which works well. I suggest a 40106 or 74AHCT14. However,
                                                    this needs a second IC.

                                                    A better solution is to make the sensor have Schmitt
                                                    action. The first version was:
                                                    http://www.redrok.com/images/beamstepper7a.gif
                                                    The problem was that it worked over a limited voltage
                                                    range.

                                                    http://www.redrok.com/images/beamstepper7e.gif
                                                    works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                                    latch similar in operation to an SCR.

                                                    Let's start with the left side without the LEDs.
                                                    Initially no current flows. The series resisters
                                                    R5 & R2 cause a small bias current to flow in the base
                                                    of Q1. Which pass current through R1 causing Q3 to
                                                    conduct. Since Q3 shorts out R5 the current through
                                                    R2 doubles. The output at the collector of Q1 snaps
                                                    high disabling the connected buffer.

                                                    (Note, R5 & R6 aren't actually required. It turns
                                                    out that leakage currents in the transistors is enough
                                                    to get started. I tried many transistors and never found
                                                    one that didn't work as expected. Prudent circuit design
                                                    demands that R5 & R6 be included because one might find
                                                    a transistor that is so perfect it won't work. Bummer. )

                                                    The now connected and lit LED1 has the ability to
                                                    absorb the current through R2 starving Q1 which
                                                    switches off resulting in the output snapping low.
                                                    Q3 also switches off reducing the bias current
                                                    in R2 to 1/2. This condition persists until the
                                                    LED goes dark.

                                                    You might ask where the current for the other side of
                                                    the LED comes from. It is from base of Q2 on the right
                                                    side. Actually, when the left side is turned off the
                                                    right side is turned on doubly as the current from
                                                    both R2 and R3 go through the base.

                                                    The right side works the same way. Since the LEDs
                                                    are connected anti parallel only one latch can
                                                    be off at a time. This is safe for the buffers.

                                                    When both of the quad buffers are supposed to be off
                                                    it is essential that all inputs not be near the
                                                    threshold to have the lowest idle current. R13 & R14
                                                    ensure that all inputs be near ground. All inputs
                                                    are connected to R13 or R14 either directly, through
                                                    input resisters, or through the stepper motor. I
                                                    added R15 & R16 for testing when the stepper motor
                                                    is disconnected. If the motor is permanently
                                                    connected R15 & R16 aren't needed. R13 & R14 can also
                                                    be connected to VCC. They don't even need to be to
                                                    the same voltage, although it operates quicker if
                                                    they are the same.

                                                    I have tested this circuit with about 25 different
                                                    74AC240s. They all worked as expected.

                                                    I ran the circuit from about 2.4V to 8.5V.
                                                    OK, one shouldn't go past 7V to be within the specs
                                                    of the 74AC240.

                                                    The sensor section was tested to 40V. It still works
                                                    well, the sensitivity is less because the bias current
                                                    is proportional to voltage which requires brighter
                                                    illumination to work.

                                                    The step patterns are not perfectly symmetrical because
                                                    this is essentially an analog circuit. Some resister
                                                    adjustment can be done.

                                                    To change the speed of the motor adjust the capacitor
                                                    values. Note, all three need to be the same value.

                                                    I have chosen the time constants of R9-C2 & R12-C3
                                                    to be about 3/4ths of R8-C1. Try to keep these ratios.
                                                    ( BTW, I'm not sure this is the exact ratio but it
                                                    seams about right. )

                                                    The 10M resisters in the sensor are the largest
                                                    commonly available resisters in 1/8W size. I tried
                                                    22M in 1/4W and that worked well with added
                                                    sensitivity. I suppose if you could find 100M they
                                                    would work even better.

                                                    I have a variation which is even more sensitive to
                                                    low light levels. Ask me if you want this variation.

                                                    I have to thank Wilf for his invaluable help in the
                                                    circuit design. Thanks Wilf.

                                                    Have fun, Duane

                                                    --
                                                         Home of the $35 LED solar tracker.
                                                        http://www.redrok.com/electron.htm#led3
                                                       CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                                      Powered by\    \ \     \      \ \\   \      \      [*]
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                                                                   \    \ \     \      \ /\ / \/  /  /  / |
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                                                                      \ /  \ \/    /     /\ \\ / \   /  / |
                                                    "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                                    Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                                    1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                                    White Bear Lake, Minnesota                \ \     /   |
                                                    USA         55110-3364                     \ \        |
                                                    (651)635-5O65    work                       \ \  /    |
                                                    (651)426-4766   home  use Courier New Font   \ \      |
                                                    (413)556-659O  Fax                copyright   \ /     |
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                                                  • Conan the Librarian
                                                    Duane, With your permission, I d like to put up a page on Solarbotics.net for this circuit design. I d just grab text & schematics from postings to date, so
                                                    Message 25 of 27 , Nov 11, 2002
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                                                      Duane,

                                                      With your permission, I'd like to put up a page on Solarbotics.net for this circuit design. I'd just grab text & schematics from postings to date, so it wouldn't take a minute of your time. This should ease folks' access to the circuit and its history, in the future.

                                                      Would this be OK with you?

                                                      Conan
                                                      -----------------------------------------------------------------
                                                      Conan the Librarian (conan.librarian@...)
                                                      Custodian of the BEAM Reference Library at http://solarbotics.net
                                                    • Duane C. Johnson
                                                      Hi Conan; ... Yes. That would be fine. Why don t you email me off list. I can provide color schematics and maybe edit them to more clearly visualize the
                                                      Message 26 of 27 , Nov 11, 2002
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                                                        Hi Conan;

                                                        Conan the Librarian <Conan.Librarian@...> wrote:

                                                        > With your permission, I'd like to put up a page on
                                                        > Solarbotics.net for this circuit design. I'd just
                                                        > grab text & schematics from postings to date, so it
                                                        > wouldn't take a minute of your time. This should ease
                                                        > folks' access to the circuit and its history, in the future.

                                                        > Would this be OK with you?

                                                        Yes. That would be fine.

                                                        Why don't you email me off list.
                                                        I can provide color schematics and maybe edit them
                                                        to more clearly visualize the operation of
                                                        http://www.redrok.com/images/beamstepper7e.gif
                                                        and several variations suggested by Wilf.

                                                        Also, the
                                                        http://www.redrok.com/images/ledsensors.gif
                                                        diagrams need circuit explanations
                                                        so others may use and enhance them.

                                                        > Conan
                                                        > -----------------------------------------------------------------
                                                        > Conan the Librarian (conan.librarian@...)
                                                        > Custodian of the BEAM Reference Library at http://solarbotics.net

                                                        Duane

                                                        --
                                                        Home of the $35 LED solar tracker.
                                                        http://www.redrok.com/electron.htm#led3
                                                        CUL8ER \ \ \ \ \ \\ \ \ Receiver
                                                        Powered by\ \ \ \ \ \\ \ \ [*]
                                                        Thermonuclear \ \Solar\Energy\from the Sun \ /////|
                                                        Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
                                                        \ \ \ \ \ /\ / \/ / / / |
                                                        WA0VBE \ \ \ \ / /\ \/ / / \/ /|
                                                        Ziggy \ \ \/ / / \ \/ \/ /\ |
                                                        \ / \ \/ / /\ \\ / \ / / |
                                                        "Red Rock Energy" === ===\ / \ / \ === \ / ===
                                                        Duane C. Johnson, Designer=== === \ \ === / |
                                                        1825 Florence St Mirrors,Heliostats,Controls & Mounts|
                                                        White Bear Lake, Minnesota \ \ / |
                                                        USA 55110-3364 \ \ |
                                                        (651)635-5O65 work \ \ / |
                                                        (651)426-4766 home use Courier New Font \ \ |
                                                        (413)556-659O Fax copyright \ / |
                                                        (651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
                                                        redrok@... (my primary email: address) \ |
                                                        redrok2@... (Hotmail address) \ |
                                                        duane.johnson@... (Unisys address) \ |
                                                        http://www.redrok.com/index.htm (My New Web site) \|
                                                        These are my opinions, and not that of Unisys Corp. ===
                                                      • Duane C. Johnson
                                                        Hi Wilf; ... When bread boarding the circuits I found there was little difference in timing when high valued input resisters were used. So, when I design with
                                                        Message 27 of 27 , Nov 11, 2002
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                                                          Hi Wilf;

                                                          Wilf Rigter wrote:

                                                          > Now a question on the Beamish Stepper Motor Circuit:

                                                          > Since the values of the series input resistors are the
                                                          > same order of magnitude as the RC timing  resistors and
                                                          > their effect on the time constant can not be ignored,
                                                          > I am curious how you decided on using those particular
                                                          > values.

                                                          When bread boarding the circuits I found there was little
                                                          difference in timing when high valued input resisters
                                                          were used. So, when I design with CMOS I usually try to
                                                          use lower values when appropriate. Mainly to prevent
                                                          board leakage currents from disrupting operation.

                                                          My solar trackers must operate in severe environments
                                                          where moisture may condense.

                                                          Secondly, lower input values can decrease power
                                                          requirements by increasing switching speed.

                                                          Thirdly, I don't have a complete set of resisters to
                                                          experiment with so I used what I have.

                                                          On the subject of limiting the input and output currents.
                                                          One should not rely on even the 20mA value as the CMOS
                                                          circuit structures can sometimes latchup. This problem
                                                          is lessened in modern CMOS but can occur. I occasionally
                                                          observe this when bread boarding so I usually have a
                                                          power supply input protection resister to prevent
                                                          damage when experimenting.

                                                           Hello Duane et al, The input resistors and actual component values were omitted for clarity and to show the similarity to monocore circuit. The modfied circuit using the input resistors and the same component values as the original is shown here inline or attached:  When 74HC or AC devices used in applications as relaxation oscillators, the external input resistors are often omitted by design and the input diodes are intentionally used to clamp the input voltage of the timing capacitor. The literature specifies 20ma as the absolute maximum clamping current. While I cannot recommend  exceeding this, 20ma  is quite conservative and higher peak input currents are usually tolerated. 
                                                           
                                                            Oscillators or networks using 74HC/AC parts in quasi-linear applications, like the microcore and bicore, use capacitive coupling. The switching of partially charged capacitors generates potential overvoltages in excess of Vcc/2 at the inputs. If no external series input resistor the transient at the input will be current limited by the internal 100 ohm series polysilicon resistor and will be voltage limited by driver output voltage drop in series with the input internal resistor  and the dynamic impedance of the clamping diodes. For Vcc= 5V  the transient potential overvoltage is 2.5V and the combined internal output and input resistance plus the diode drop would limit the current to less than 20ma even if no external input resistor is used. However, there are other good reasons to include the series resistor related to frequency and dutycyle stability. Applications notes often suggest using a series resistor value of 10x the feedback resistor value to avoid clamping the AC coupled feedback signal. Not calmping the feedback signal effectively increases the RC time constant, decreases power consumption and, importantly, averages the DC level at the input near the threshold.  The latter tends to move the dutycyle of the oscilator automatically toward a symmetrical waveform.  One of my earliest posts to this list described an using series input resistors in an article called Belted and Suspended Bicores including a  method to control of the average dc voltage at the input which can be used to adjust the dutycycle. To complicate matters a little bit, the Beamish Stepper Motor circuit outputs directly drive the stepper coils. The inductive load generates its own transients at the outputs which may exceed the output diode ratings Moreover motor loading of the output causes a voltage drop which together with  switching transients can be coupled back through the feedback capacitor to the inputs and can cause timing instability.  This motor load volatge drop is proportional to motor current and can be put to some good use in other applications to truncate the oscillator cycle and reverse a heavily overloaded motor.  For some applications it is desirable to control the duty cycle of a slave bicore (e.g. turning in a bicore walker by injecting a dc current into the input node) but the averaging effect of adding series input resistors would oppose the dc control signal and must be taken into account in such a design. Now a question on the Beamish Stepper Motor Circuit: Since the values of the series input resistors are the same order of magnitude as the RC timing  resistors and their effect on the time constant can not be ignored,  I am curious how you decided on using those particular values. best regard wilf
                                                          ----- Original Message -----
                                                          Sent: Sunday, November 10, 2002 7:30 AM
                                                          Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                                                           Hi All;

                                                          I find that input protection resisters are required for safety of the inputs
                                                          in AC gates.
                                                          The spec limits the input or out protection diodes to 20mA.
                                                          The outputs can drive several hundred mAs. Clearly this can
                                                          damage the inputs with current fed back through the capacitors.

                                                          The protection resistors weren't as important with the lower
                                                          powered CMOS families.

                                                          The minimum resistance is, in this case, based on VCC and
                                                          the worst case threshold votage.
                                                          ( VCC - 30% * VCC ) / 20mA = R
                                                          ( 7V - 30% * 7V ) / 20mA = 245 ohms

                                                          Prudent design calls for a minimum of about 10K.

                                                          BTW, this is not just academic. I did blow of a couple of AC ICs
                                                          because of this. Remember these are powerful chips.
                                                           


                                                          http://www.redrok.com/images/beamstepper7f.gif

                                                          Neat! Now there are about 5 distinct variations of this basic design.

                                                          Duane

                                                          Wilf Rigter wrote:

                                                          Here is yet another variation of the stepper circuit, somewhat easier to read and clearly shows the master slave monocore topology. Note that in this case the resistors for the slave monocores are connected to the complementary outputs of the master monocore.---- Original Message -----
                                                          Sent: Saturday, November 09, 2002 9:08 AM
                                                          Subject: Re: [beam] Re: Beamish Stepper Motor Driver
                                                           Hi All;

                                                          Wilf and I have been developing another solar tracker
                                                          that is based on a 74AC240 Dual Quad Tristate Buffer.
                                                          There have been a number of variations. This is
                                                          the results. See:
                                                          http://www.redrok.com/images/beamstepper7e.gif

                                                          The 74AC240 stepper driver works by enabling each half
                                                          of the buffer. Only one half can be enabled at a time.

                                                          Let's assume that the top half of the driver is enabled.
                                                          U1A & U1B along with R8, C1, & the input protection
                                                          resister R7 form a square wave oscillator. The outputs
                                                          of U1A & U1B directly drive one coil of a bipolar stepper
                                                          motor.

                                                          U1C & U1D along with R9, C2, & the input protection
                                                          resister R10 form a 90 degree phase shift. The outputs
                                                          of U1C & U1D directly drive the other coil of the bipolar
                                                          stepper motor. The motor turns in one direction.

                                                          If the second bottom half of the driver is enabled the
                                                          oscillator using U1E & U1F work as before. U1H & U1G
                                                          along with R12, C3, & the input protection
                                                          resister R11 form a 90 degree phase shift. Except it's
                                                          connected the other way around from before so it's
                                                          actually 270 degrees. The outputs of U1H & U1G directly
                                                          drive the other coil of the bipolar stepper motor. The
                                                          motor turns in the other direction. Neat, Huh!

                                                          An earlier version of the circuit didn't work well
                                                          because the the sensors presented an analog enable
                                                          signal. This was sometimes at the threshold voltage
                                                          which caused the buffer to have high idle current and
                                                          sometimes cross coupling which was a bad thing. %^(

                                                          What was needed was a sensor that had a Schmitt trigger
                                                          input. This could be done using a Schmitt trigger gate
                                                          which works well. I suggest a 40106 or 74AHCT14. However,
                                                          this needs a second IC.

                                                          A better solution is to make the sensor have Schmitt
                                                          action. The first version was:
                                                          http://www.redrok.com/images/beamstepper7a.gif
                                                          The problem was that it worked over a limited voltage
                                                          range.

                                                          http://www.redrok.com/images/beamstepper7e.gif
                                                          works better. Q1 & Q3 and Q2 & Q4 each form a bistable
                                                          latch similar in operation to an SCR.

                                                          Let's start with the left side without the LEDs.
                                                          Initially no current flows. The series resisters
                                                          R5 & R2 cause a small bias current to flow in the base
                                                          of Q1. Which pass current through R1 causing Q3 to
                                                          conduct. Since Q3 shorts out R5 the current through
                                                          R2 doubles. The output at the collector of Q1 snaps
                                                          high disabling the connected buffer.

                                                          (Note, R5 & R6 aren't actually required. It turns
                                                          out that leakage currents in the transistors is enough
                                                          to get started. I tried many transistors and never found
                                                          one that didn't work as expected. Prudent circuit design
                                                          demands that R5 & R6 be included because one might find
                                                          a transistor that is so perfect it won't work. Bummer. )

                                                          The now connected and lit LED1 has the ability to
                                                          absorb the current through R2 starving Q1 which
                                                          switches off resulting in the output snapping low.
                                                          Q3 also switches off reducing the bias current
                                                          in R2 to 1/2. This condition persists until the
                                                          LED goes dark.

                                                          You might ask where the current for the other side of
                                                          the LED comes from. It is from base of Q2 on the right
                                                          side. Actually, when the left side is turned off the
                                                          right side is turned on doubly as the current from
                                                          both R2 and R3 go through the base.

                                                          The right side works the same way. Since the LEDs
                                                          are connected anti parallel only one latch can
                                                          be off at a time. This is safe for the buffers.

                                                          When both of the quad buffers are supposed to be off
                                                          it is essential that all inputs not be near the
                                                          threshold to have the lowest idle current. R13 & R14
                                                          ensure that all inputs be near ground. All inputs
                                                          are connected to R13 or R14 either directly, through
                                                          input resisters, or through the stepper motor. I
                                                          added R15 & R16 for testing when the stepper motor
                                                          is disconnected. If the motor is permanently
                                                          connected R15 & R16 aren't needed. R13 & R14 can also
                                                          be connected to VCC. They don't even need to be to
                                                          the same voltage, although it operates quicker if
                                                          they are the same.

                                                          I have tested this circuit with about 25 different
                                                          74AC240s. They all worked as expected.

                                                          I ran the circuit from about 2.4V to 8.5V.
                                                          OK, one shouldn't go past 7V to be within the specs
                                                          of the 74AC240.

                                                          The sensor section was tested to 40V. It still works
                                                          well, the sensitivity is less because the bias current
                                                          is proportional to voltage which requires brighter
                                                          illumination to work.

                                                          The step patterns are not perfectly symmetrical because
                                                          this is essentially an analog circuit. Some resister
                                                          adjustment can be done.

                                                          To change the speed of the motor adjust the capacitor
                                                          values. Note, all three need to be the same value.

                                                          I have chosen the time constants of R9-C2 & R12-C3
                                                          to be about 3/4ths of R8-C1. Try to keep these ratios.
                                                          ( BTW, I'm not sure this is the exact ratio but it
                                                          seams about right. )

                                                          The 10M resisters in the sensor are the largest
                                                          commonly available resisters in 1/8W size. I tried
                                                          22M in 1/4W and that worked well with added
                                                          sensitivity. I suppose if you could find 100M they
                                                          would work even better.

                                                          I have a variation which is even more sensitive to
                                                          low light levels. Ask me if you want this variation.

                                                          I have to thank Wilf for his invaluable help in the
                                                          circuit design. Thanks Wilf.

                                                          Have fun, Duane

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                                                               Home of the $35 LED solar tracker.
                                                              http://www.redrok.com/electron.htm#led3
                                                             CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                                            Powered by\    \ \     \      \ \\   \      \      [*]
                                                           Thermonuclear    \ \Solar\Energy\from the Sun \ /////|
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                                                            Ziggy          \    \ \/    /    / \ \/   \/    /\  |
                                                                            \ /  \ \/    /     /\ \\ / \   /  / |
                                                          "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                                          Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                                          1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                                          White Bear Lake, Minnesota                \ \     /   |
                                                          USA         55110-3364                     \ \        |
                                                          (651)635-5O65    work                       \ \  /    |
                                                          (651)426-4766   home  use Courier New Font   \ \      |
                                                          (413)556-659O  Fax                copyright   \ /     |
                                                          (651)583-2O62 Red Rock Energy Site (C)980907  ===\    |
                                                          redrok@...     (my primary email: address) \   |
                                                          redrok2@...              (Hotmail address) \  |
                                                          duane.johnson@...          (Unisys  address) \ |
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                                                          These are my opinions, and not that of Unisys Corp.  ===
                                                           


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                                                          --
                                                               Home of the $35 LED solar tracker.
                                                              http://www.redrok.com/electron.htm#led3
                                                             CUL8ER  \    \ \     \      \ \\   \      \  Receiver
                                                            Powered by\    \ \     \      \ \\   \      \      [*]
                                                           Thermonuclear    \ \Solar\Energy\from the Sun \ /////|
                                                          Energy(the Sun)    \ \     \      \ \\   \ / / /\/ / /|
                                                                         \    \ \     \      \ /\ / \/  /  /  / |
                                                             WA0VBE       \    \ \     \ /   /\ \/   /   /  \/ /|
                                                            Ziggy          \    \ \/    /    / \ \/   \/    /\  |
                                                                            \ /  \ \/    /     /\ \\ / \   /  / |
                                                          "Red Rock Energy" ===  ===\ /   \ /    \ ===  \ /    ===
                                                          Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                                                          1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                                                          White Bear Lake, Minnesota                \ \     /   |
                                                          USA         55110-3364                     \ \        |
                                                          (651)635-5O65    work                       \ \  /    |
                                                          (651)426-4766   home  use Courier New Font   \ \      |
                                                          (413)556-659O  Fax                copyright   \ /     |
                                                          (651)583-2O62 Red Rock Energy Site (C)980907  ===\    |
                                                          redrok@...     (my primary email: address) \   |
                                                          redrok2@...              (Hotmail address) \  |
                                                          duane.johnson@...          (Unisys  address) \ |
                                                          http://www.redrok.com/index.htm    (My New Web site) \|
                                                          These are my opinions, and not that of Unisys Corp.  ===
                                                           

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