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Re: [beam] monostable multivibrator

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  • julian plante
    only one way to be sure. Have a breadboard? My guess is that it depends on the capacitor size. ... __________________________________________________ Do You
    Message 1 of 5 , Apr 1 5:36 PM
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      only one way to be sure. Have a breadboard? My guess is that it depends on
      the capacitor size.

      --- "R. Martin Keen" <keenerd@...> wrote:
      > just wondering: would the attached work as an +V edge triggered
      > monostable multivibrator? It needs to have the same time constant
      > regardless of the -V edge (length of input pulse). I know I could do
      > this with a 555 timer, but I need 8ish of these, so less parts is good.
      >
      > First person to reply (with competence) gets to know what its for.
      >
      > -Martin
      >
      > THE resource for beginners
      > http://beamlinks.botic.com
      > "The best of everyone's BEAM"
      >
      >
      > To unsubscribe from this group, send an email to:
      > beam-unsubscribe@egroups.com
      >
      >
      >
      > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
      >
      >

      > ATTACHMENT part 2 image/gif name=circuit.gif



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    • Wilf Rigter
      That won t work. A diode in series with a cap will charge it but there is no path for discharge. The minimum solution requires two inverters, a diode, two
      Message 2 of 5 , Apr 1 8:28 PM
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        That won't work. A diode in series with a cap will charge it but there is no
        path for discharge. The minimum solution requires two inverters, a diode,
        two resistors and a cap for each monostable. There is a slightly simpler
        method which I described in my Nu rings 101 paper.
        For 8 monos with identical fixed pulse widths you need 2 HC240, 2 resistor
        networks, 8 diodes and 8 caps. Depending on the application there may be a
        much more efficient solution that does not require monos.

        wilf

        -----Original Message-----
        From: R. Martin Keen
        To: beam@yahoogroups.com
        Sent: 4/1/02 3:26 PM
        Subject: [beam] monostable multivibrator

        just wondering: would the attached work as an +V edge triggered
        monostable multivibrator? It needs to have the same time constant
        regardless of the -V edge (length of input pulse). I know I could do
        this with a 555 timer, but I need 8ish of these, so less parts is good.

        First person to reply (with competence) gets to know what its for.

        -Martin

        THE resource for beginners
        http://beamlinks.botic.com
        "The best of everyone's BEAM"
      • Wilf Rigter
        Another probable repeat email cause Yahoo is painfully slow. Hi Martin, That won t work. A diode in series with a cap will charge it but there is no path for
        Message 3 of 5 , Apr 2 12:23 AM
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          Another probable repeat email cause Yahoo is painfully slow.

          Hi Martin,

          That won't work. A diode in series with a cap will charge it but there
          is no path for discharge.

          Attached are two examples of the circuit which is variously known as the
          monostable, pulsestretcher or oneshot. Both circuits have an output pulse
          width that is independent of the input waveform. The AND gate version is
          slightly more compact but requires an input waveform with a fast falling
          edge. It requires 2 chips for 4 monostable circuits. The R1C1 product must
          be small compared to the R2C2 product which sets the active low output pulse
          width.

          The 2 Schmitt inverter monostable triggers from a negative slope slow
          changing or DC level input waveform. It must use Schmitt triggers: 74HC240s
          will generate multiple output transitions. With 6 inverters per IC this
          circuit requires 3 chips for 9 monostable circuits. Only the non-inverted
          output has true monostable pulses. Note that at TP3 an inverted waveform is
          available which is the OR of the TP1 and TP5 wavforms. This Or'd waveform
          may be useful in special applications.

          The waveforms at key points in the ciruit are shown. Note both long and
          short input pulses generate the same output pulse. Both circuits are non-
          retriggerable ie the output pulse width is constant even is multiple input
          trigger pulses occur. The circuits will not accept a new trigger until the
          last pulse has timed out.

          Depending on the application there may be a more efficient solution that
          does not require 8 monostables

          enjoy

          wilf


          -----Original Message-----
          From: R. Martin Keen
          To: beam@yahoogroups.com
          Sent: 4/1/02 3:26 PM
          Subject: [beam] monostable multivibrator

          just wondering: would the attached work as an +V edge triggered
          monostable multivibrator? It needs to have the same time constant
          regardless of the -V edge (length of input pulse). I know I could do
          this with a 555 timer, but I need 8ish of these, so less parts is good.

          First person to reply (with competence) gets to know what its for.

          -Martin

          THE resource for beginners
          http://beamlinks.botic.com
          "The best of everyone's BEAM"


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



          Your use of Yahoo! Groups is subject to
          http://docs.yahoo.com/info/terms/

          <<circuit.gif>>
        • R. Martin Keen
          Wilf: I missed something on the original schematic. There should be a second cap in parallel with the resistor. So, in the mind, the positive leading edge
          Message 4 of 5 , Apr 2 7:39 PM
          • 0 Attachment
            Wilf: I missed something on the original schematic. There should be a
            second cap in parallel with the resistor.

            So, in the mind, the positive leading edge goes through the cap, through
            the diode, charges the second cap, and switches the inverter. The
            negative trailing edge goes though the cap and is blocked by the diode.
            The grounded resistor/cap act as an Nv neuron (sorta) and time out when
            ever they feel like. Would this work?

            -Martin

            THE resource for beginners
            http://beamlinks.botic.com
            "The best of everyone's BEAM"


            On Tue, 2 Apr 2002 00:23:45 -0800 Wilf Rigter
            <Wilf.Rigter@...> writes:
            >
            > Another probable repeat email cause Yahoo is painfully slow.
            >
            > Hi Martin,
            >
            > That won't work. A diode in series with a cap will charge it but
            > there
            > is no path for discharge.
            >
            > Attached are two examples of the circuit which is variously known as
            > the
            > monostable, pulsestretcher or oneshot. Both circuits have an output
            > pulse
            > width that is independent of the input waveform. The AND gate
            > version is
            > slightly more compact but requires an input waveform with a fast
            > falling
            > edge. It requires 2 chips for 4 monostable circuits. The R1C1
            > product must
            > be small compared to the R2C2 product which sets the active low
            > output pulse
            > width.
            >
            > The 2 Schmitt inverter monostable triggers from a negative slope
            > slow
            > changing or DC level input waveform. It must use Schmitt triggers:
            > 74HC240s
            > will generate multiple output transitions. With 6 inverters per IC
            > this
            > circuit requires 3 chips for 9 monostable circuits. Only the
            > non-inverted
            > output has true monostable pulses. Note that at TP3 an inverted
            > waveform is
            > available which is the OR of the TP1 and TP5 wavforms. This Or'd
            > waveform
            > may be useful in special applications.
            >
            > The waveforms at key points in the ciruit are shown. Note both long
            > and
            > short input pulses generate the same output pulse. Both circuits are
            > non-
            > retriggerable ie the output pulse width is constant even is multiple
            > input
            > trigger pulses occur. The circuits will not accept a new trigger
            > until the
            > last pulse has timed out.
            >
            > Depending on the application there may be a more efficient solution
            > that
            > does not require 8 monostables
            >
            > enjoy
            >
            > wilf
            >
            >
            > -----Original Message-----
            > From: R. Martin Keen
            > To: beam@yahoogroups.com
            > Sent: 4/1/02 3:26 PM
            > Subject: [beam] monostable multivibrator
            >
            > just wondering: would the attached work as an +V edge triggered
            > monostable multivibrator? It needs to have the same time constant
            > regardless of the -V edge (length of input pulse). I know I could
            > do
            > this with a 555 timer, but I need 8ish of these, so less parts is
            > good.
            >
            > First person to reply (with competence) gets to know what its for.
            >
            > -Martin
            >
            > THE resource for beginners
            > http://beamlinks.botic.com
            > "The best of everyone's BEAM"
            >
            > ------------------------ Yahoo! Groups Sponsor
            >
            > To unsubscribe from this group, send an email to:
            > beam-unsubscribe@egroups.com
            >
            >
            >
            > Your use of Yahoo! Groups is subject to
            > http://docs.yahoo.com/info/terms/
            >
            > <<circuit.gif>>
            >


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