Electronics Need a timer circuit

Discussion in 'Modding' started by c.cam108, 25 Oct 2004.

  1. c.cam108

    c.cam108 Minimodder

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    I have made a circuit to control servos from a guide on the internet, and there is a problem with it. I won't go into detail, but basically I need a circuit that, when an input of either 5v or 0v is changed (eg. was 5v, now 0v), the output goes high to turn on the servo, and after around a second, goes low again to turn it off.

    I would rather not use a PIC for this, and would rather use a 555 if possible. I have a few logic chips lying around that I could use.

    I need a quick reply to this if possible.

    Thanks.

    _C
     
    c.cam108, 25 Oct 2004
    #1
  2. theshadow27

    theshadow27 What's a Dremel?

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    i wrote this up a little while ago to help a mate with turning a regular switch into a momentary switch.

    http://www.xoxideforums.com/showthread.php?t=41255

    you could easly adapt it to your purposes. btw... standerd hobby servos use PWM, not just voltage, unless you hack out the PWM board and POT, and connect wires to the motor
     
    theshadow27, 25 Oct 2004
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  3. c.cam108

    c.cam108 Minimodder

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    Thanks for that shadow.

    I m having a problem with the circuit though. When I tie the input low (using the switch), the LED stays on constantly. When I disconnect it, it goes off instantly, unless the switch was on for a very short length of time.

    Any ideas?

    Thanks

    _C
     
    c.cam108, 25 Oct 2004
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  4. theshadow27

    theshadow27 What's a Dremel?

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    do you have the pullup resistor on the correct side of the switch? its important

    also, do you have discharge and threshold pulled up? thats important too

    and are you switching reset, or trigger? if you switch reset, it will stay lit as long as the switch is held. if you switch trigger, when the timing period ends the led will turn off even if its still held
     
    theshadow27, 25 Oct 2004
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  5. c.cam108

    c.cam108 Minimodder

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    Yes, yes and trigger.

    Strange...

    _C
     
    c.cam108, 25 Oct 2004
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  6. Xiachunyi

    Xiachunyi What's a Dremel?

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    Use a NAND gate array attached to a 555 IC timer wired in one-shot mode. The output pulse will not be emitted unless there is a change on the NAND gates input, i.e. from high to low or from low to high regardless.

    Schematic Here

    This should be what you want to do unless I have not understood you correctly. Hope this helps!
     
    Xiachunyi, 25 Oct 2004
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  7. c.cam108

    c.cam108 Minimodder

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    Thanks, I'll try that out soon. As luck would ave it, I have two 74LS00's here!

    I might not need it now. I think it was a dodgy servo and the H-bridge on it just recently went up in smoke. I have two more different servos on the way.

    Thanks anyway.

    _C
     
    c.cam108, 26 Oct 2004
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