pulse delay

Discussion in 'General Electronics Chat' started by kballing, Jul 23, 2007.

  1. kballing

    Thread Starter Member

    Jun 18, 2007
    18
    0
    Hi all,
    I've designed a circuit that seems to work well, but I've overlooked one small thing.

    The circuit controls two solenoid valves. A signal triggers a monostable multivibrator which converts that pulse to a longer pulse. As is stands right now, a button is pushed and the output signal turns on both valves for 300ms. What I need to have happen is this. I push a button and valve one turns on for 300ms and then after the 300ms, valve 2 turns on for more than 300ms. What sort of circuit element do I need to insert to delay the signal to valve 2?

    You can think of it as an arm throwing a ball. Valve 1 makes the arm move, and valve 2 lets go of the ball so to speak, without closing too soon.
     
  2. John Luciani

    Active Member

    Apr 3, 2007
    477
    0
    Another monostable. Have one monostable trigger a second one.

    (* jcl *)
     
  3. gootee

    Senior Member

    Apr 24, 2007
    447
    50
    It sounds like you might need to come up with a simple circuit that will generate a trigger pulse from a falling pulse edge but not from a rising edge. Then you could use that to trigger your second monostable from the end of the first monostable's pulse.

    If you would give the details of the existing and the needed pulse voltages, available supply voltages, etc, someone will probably come up with a simple circuit for you. It should be able to be done with just a few discrete components, or maybe a logic gate or two.

    It sounds like you might be able to just use an inverter to feed the output of the first monostable to the input of the second one. But give us the details of what you have and what you need.

    - Tom Gootee

    http://www.fullnet.com/~tomg/index.html

    -
     
  4. kballing

    Thread Starter Member

    Jun 18, 2007
    18
    0
    The signals that I have are this
    Pushbutton _______i--------i___________________________________
    monostable ________i--------300ms----------i____________________
    What I need from
    monostable2 ______________________________i---------------i_______
    I could use the signal from monostable 1 to trigger monostable 2 but I need a delay and it is not simply an inverted signal.
     
  5. kballing

    Thread Starter Member

    Jun 18, 2007
    18
    0
    the monostable multivibrator is part SN74LS123, all the signals are 5V and the pulse width is controlled by an external RC circuit
     
  6. John Luciani

    Active Member

    Apr 3, 2007
    477
    0
    Delay the trigger of monostable2 using an RC and a schmitt trigger buffer.

    (* jcl *)
     
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