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Suggestions for Digital Timing Circuit

Discussion in 'Electronic Design' started by [email protected], Mar 23, 2006.

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  1. Guest

    Hi All.

    I'd like to build a digital timing circuit and thought I'd see if
    anyone might be able to offer some suggestions. I'd like to create a
    timing circuit (all digital, if possible) which can take an input pulse
    of approx. 500 ms and then, 5-10 seconds later, output a pulse of
    somewhere between 500 ms - 1 second. Furthermore, I'd like to be able
    to tweak the delay time, but I don't need a great deal of resolution
    with the tweaking (if I could have timing increments of 1 second, that
    would be just fine), and as I said previously, I only need a delay time
    of 5 - 10 seconds. I know that this type of circuit could be easily
    constructed using a 555 in association with other circuitry, but I'm
    curious as to whether or not there might be some type of easier
    approach using a single IC with which I could perform this relatively
    simple timing task.

    Thanks in advance to anyone who may be able to help!
  2. John_H

    John_H Guest

    Use a tiny PIC or a CPLD. Development kits are a reasonable cost and
    the rest of your twiddling with circuits can be much easier.
  3. Jimbo

    Jimbo Guest

  4. Ken Smith

    Ken Smith Guest

    This sounds like a job for CD4000 series logic.

    There are a couple of obvious ways to make the circuit.

    First version:

    (1) Clean up the pulse (so that it goes ground to Vcc etc)

    (2) Apply the pulse to the clock input of a CD4013. "D" input of CD4013
    is high. This makes a "Delay_in_progress" signal.

    (3) Do you have a clock reference? If not make one with a 32768 crystal
    and an inverter.

    (4) Divide your clock reference down to 1Hz in a resetable counter such as
    CD4060+CD4013. Attach "reset" to the not(Delay_in_progress)

    (5) Use the divided clock to clock a CD4017. Reset this also with

    (6) Wire the last state of the CD4017 to the reset pin of the 1st CD4013

    (7) You now have a nice list of outputs on the CD4017 run them to a rotary
    switch to select the one you want. If you use a 2 deck 12 position
    switch you can make this the on/off switch too.

    (8) Take the selected pulse and use it to drive something like a TIP-35 to
    make a hard to break output.

    (9) Mount it all in a box with a 9V battery holder etc.

    Second version:

    (1)..(3) as before.

    (4) Divide oscillator down to less than 10KHz with method of choice.

    (5) Connect two CD4059s to the "10KHz" clock. Connect thumb wheel switches
    to both.

    (6) The first CD4059 is held reset by not(Delay_in_progress) and its
    output resets the Delay_in_progress flip-flip.

    (7) The 2nd section of the CD4013 is clocked by the output of the 1st
    CD4059. This makes an "Output_in_progress" pulse.

    (8) The 2nd CD4059 is held reset by the not(Output_in_progress)

    (9) The second CD4059's output resets the 2nd CD4013 section.

    (10) buffer the signal as suggested in 1st version and mount in a box.
  5. Fred Bloggs

    Fred Bloggs Guest

    I'd like to build a digital timing circuit and thought I'd see if
    Radio Shack sells the 556 dual 555. Use that: an adjustable 5-10 second
    one-shot followed by a 500ms one-shot. Are you too good for Radio Shack
    or something?
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