"TIMED" Power on delay circuit.

Discussion in 'The Projects Forum' started by haxxx, Jul 16, 2011.

  1. haxxx

    Thread Starter Active Member

    Feb 14, 2009
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    I've built this power on delay 555 circuit which works just fine.
    However what i need is a timed power on delay.
    That is, after switch is pressed there is a 5 sec delay,
    then relay latches for 5 seconds then deactivates, ready for another switch press.
    I tried using a 10 sec 555 timer before the "power on delay 555" circuit,
    that is: pin 3 of the 555 timer will provide vcc to pin 8 of the "power on delay 555". seems crude i know, novice.
    For some reason this cancels the timing circuit in the "power on delay 555" circuit,
    load just stays on.
    Any ideas, would be appreciated.

    Regards,
    Richard
     
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
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    68
    I believe what you are looking for is this:

    You will have to add the relay at the output of 555B pin 3.

    [​IMG]

    His other circuits can be found at: Model Railroad & Misc. Electronics
     
    Last edited: Jul 17, 2011
  3. haxxx

    Thread Starter Active Member

    Feb 14, 2009
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    0
    I think this will work, many thanks.

    haxxx
     
  4. haxxx

    Thread Starter Active Member

    Feb 14, 2009
    35
    0
    The two stage 555 delay circuit works fine but is false triggering
    on Timer B(output) when power is applied.
    I tried incorporating the cycle canceling method in the
    attached image, now it no longer false triggers if power is removed
    and immediately re-applied. It only happens when power is removed
    for several minutes, any ideas i used a bc548 for the canceling switch
    a 100k resistor, and tried both a 1 and 22uf cap. I also tried adding that cap to
    ground on pin 2 but second timer B didn't trigger at all when Timer A ran out.
    Any ideas?
     
    Last edited: Jul 21, 2011
  5. iONic

    AAC Fanatic!

    Nov 16, 2007
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    What is your Vcc and what is the capacitor rated voltage. I suspect that the cap is fully discharged before you are reapplying power to the circuit.

    How about a pic of your circuit, in .png format if possible.
     
  6. haxxx

    Thread Starter Active Member

    Feb 14, 2009
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    checked the transistor and realized it wasn't pulling
    the reset pin low at all. double checked and realized a small jumper i previously had on the board was shorting the base of the transistor to ground. I was pulling my hair out all day on this.
    Thanks for the response anyway.
     
  7. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Was going to suggest you check the pin config on the Transistor. Perhaps that would have led you to the error sooner. Oh well...are you working now?
     
  8. haxxx

    Thread Starter Active Member

    Feb 14, 2009
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    0
    up and working Ionic,
    Thanks, you're the man

    Haxxx.
     
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