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Re: [beam] Re: Beamish Stepper Motor Driver

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  • 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 1 of 27 , Nov 9, 2002
    • 0 Attachment
      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 2 of 27 , Nov 9, 2002
      • 0 Attachment
         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 3 of 27 , Nov 9, 2002
        • 0 Attachment
          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 4 of 27 , Nov 9, 2002
          • 0 Attachment
            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 5 of 27 , Nov 10, 2002
            • 0 Attachment
              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
                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                       \ \  /    |
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            • Scott Burns
              I was under the impression that CMOS inputs were high resistance and that very little current passed through. (?) Scott
              Message 6 of 27 , Nov 10, 2002
              • 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
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                >      Duane C. Johnson, Designer===   ===     \ \   ===  /  |
                >      1825 Florence St  Mirrors,Heliostats,Controls & Mounts|
                >      White Bear Lake, Minnesota                \ \     /   |
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                >      These are my opinions, and not that of Unisys Corp.  ===
                >
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                >      beam-unsubscribe@egroups.com
                >
                >
                >
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                >      Service.
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                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


                --
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                    http://www.redrok.com/electron.htm#led3
                   CUL8ER  \    \ \     \      \ \\   \      \  Receiver
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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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                redrok2@...              (Hotmail address) \  |
                duane.johnson@...          (Unisys  address) \ |
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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.  ===
                 
              • 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 7 of 27 , Nov 10, 2002
                • 0 Attachment
                  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

                  --
                  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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                  (651)635-5O65 work \ \ / |
                  (651)426-4766 home use Courier New Font \ \ |
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                  (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
                  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 8 of 27 , Nov 10, 2002
                  • 0 Attachment
                    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

                    --
                         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       \    \ \     \ /   /\ \/   /   /  \/ /|
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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
                     
                     

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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.  ===
                     
                  • 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 9 of 27 , Nov 10, 2002
                    • 0 Attachment
                      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\    \ \     \      \ \\   \      \      [*]
                      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.

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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 10 of 27 , Nov 10, 2002
                      • 0 Attachment
                        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

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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 11 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 12 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

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                            http://www.redrok.com/electron.htm#led3
                            CUL8ER \ \ \ \ \ \\ \ \ Receiver
                            Powered by\ \ \ \ \ \\ \ \ [*]
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                          • 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 13 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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