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Or/delay circuit- what i'll try

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  • bill rowe
    I have two nor gates free so i m going to try the following to delay my N pulse by .5 us or so. I ll probably wait til monday and get a 100pf cap and use a 5k
    Message 1 of 3 , Jun 23, 2013
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    I have two nor gates free so i'm going to try the following to delay my N pulse by .5 us or so. I'll probably wait til monday and get a 100pf cap and use a 5k resistor. The rc is theoretically ok but 33 ohms seems like a silly small resistance.
  • Lee Hart
    ... It may work; I don t fully understand the needs of the circuit that this is driving. It will delay the rising and falling edges of N; but it won t give you
    Message 2 of 3 , Jun 23, 2013
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      On 6/23/2013 8:56 AM, bill rowe wrote:
      > I have two nor gates free so i'm going to try the following to delay
      It may work; I don't fully understand the needs of the circuit that this
      is driving. It will delay the rising and falling edges of N; but it
      won't give you the timing diagram you posted.

      Your earlier timing diagram showed the OUT pulse going high when the N
      pulse went *low*. I assume this was done because that's when the
      Membership Card's output port latches the output data.

      Your present circuit sets the OUT pulse high shortly after the N pulse
      goes *high*. That could occur before there is valid output data on the
      port. If the RC time constant is made as late as possible, so OUT goes
      high just barely before N goes low, then the high-time of the OUT pulse
      is just a tiny sliver, since the RC capacitor just barely reached the
      NOR gate's switching threshold.

      If you have only two spare NOR gates, you can replace the final two NOR
      gates in my earlier circuit with a diode OR gate, like this:

      ........................................................
      ............................______......................
      N___________________________\ NOR \ .. 1N4148 ..........
      .. | ......... _____......__|. D . O_____|\|_________OUT
      .. |_/\/\______\ NOR\ ...|. /_____/ .... |/| .. | ......
      ..... R1 . |___|. C .O---...................... | ......
      ......... _|_ ./____/ ........... AVR____|\|____| ......
      ...... C1 ___ .......................... |/| .. | ......
      .......... | ..........................1N4148 . > ......
      ......... gnd ................................. > 10k ..
      ............................................... > ......
      ............................................... | ......
      .............................................. gnd .....

      --
      Any intelligent fool can make things bigger, more complex, and more
      violent. It takes a touch of genius, and a lot of courage, to move
      in the opposite direction. -- Albert Einstein
      --
      Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
    • bill rowe
      you re right lee. I was originally stuck on using the falling edge of n1 but all I really need is a delay. The shift register has been loaded on N2 s falling
      Message 3 of 3 , Jun 23, 2013
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        you're right lee.  I was originally stuck on using the falling edge of n1 but all I really need is a delay.

        The shift register has been loaded on N2's falling edge so it has what the latch has.  Now I'm shifting it out using N1.  I need the peripherals to see the rising edge of N1 to grab each bit before the shift register shifts the next bit in. Peripherals usually need <100 ns to grab the data so this should work.

        Thanks again.  I do have to do something similar for the incoming data and there i might need the more complete falling edge solution.


        To: cosmacelf@yahoogroups.com
        From: leeahart@...
        Date: Sun, 23 Jun 2013 12:21:59 -0500
        Subject: Re: [cosmacelf] Or/delay circuit- what i'll try

         
        On 6/23/2013 8:56 AM, bill rowe wrote:
        > I have two nor gates free so i'm going to try the following to delay
        It may work; I don't fully understand the needs of the circuit that this
        is driving. It will delay the rising and falling edges of N; but it
        won't give you the timing diagram you posted.

        Your earlier timing diagram showed the OUT pulse going high when the N
        pulse went *low*. I assume this was done because that's when the
        Membership Card's output port latches the output data.

        Your present circuit sets the OUT pulse high shortly after the N pulse
        goes *high*. That could occur before there is valid output data on the
        port. If the RC time constant is made as late as possible, so OUT goes
        high just barely before N goes low, then the high-time of the OUT pulse
        is just a tiny sliver, since the RC capacitor just barely reached the
        NOR gate's switching threshold.

        If you have only two spare NOR gates, you can replace the final two NOR
        gates in my earlier circuit with a diode OR gate, like this:

        ........................................................
        ............................______......................
        N___________________________\ NOR \ .. 1N4148 ..........
        .. | ......... _____......__|. D . O_____|\|_________OUT
        .. |_/\/\______\ NOR\ ...|. /_____/ .... |/| .. | ......
        ..... R1 . |___|. C .O---...................... | ......
        ......... _|_ ./____/ ........... AVR____|\|____| ......
        ...... C1 ___ .......................... |/| .. | ......
        .......... | ..........................1N4148 . > ......
        ......... gnd ................................. > 10k ..
        ............................................... > ......
        ............................................... | ......
        .............................................. gnd .....

        --
        Any intelligent fool can make things bigger, more complex, and more
        violent. It takes a touch of genius, and a lot of courage, to move
        in the opposite direction. -- Albert Einstein
        --
        Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm

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