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Need a timer diagram?

Discussion in 'General Electronics Chat' started by zone97, Jan 28, 2009.

  1. zone97

    zone97 New Member

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    Hello all, I am new here so be kind... :)

    I have a need for a VERY simple timer circuit but can not find a diagram anywhere.

    I need a circuit that I can supply 12vdc @ 1amp, and it would output the same via a relay to a small motor for 5 - 15 seconds and then stop. Can anyone help me with a diagram.

    Thank you.
     
    Last edited: Jan 29, 2009
  2. Hero999

    Hero999 Banned

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  3. duffy

    duffy New Member

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    Easier still, search on "time delay relay" at places like Mouser, Digikey and Newark. This is a very common request, and there are relays designed to do what you want, at that voltage.
     
  4. dave

    Dave New Member

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  5. zone97

    zone97 New Member

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    Thank you for the replies. I found this circuit online at eBay. However the trigger for it is a momentary ground, if the trigger is held it does not work. What can I add to this to make it so that the trigger can be constant and the unit work. (I do not have a diagram only a photo. Maybe someone will recognize this item.)

    [​IMG]
     
  6. Hero999

    Hero999 Banned

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    It looks like you need to add a DC blocking capacitor.

    Does it trigger when the input pin is connected to the 0V or +V?
     
  7. zone97

    zone97 New Member

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    Triggers on a momentary 0 (gnd)
     
    Last edited: Feb 7, 2009
  8. Hero999

    Hero999 Banned

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    Connect a 1nF capacitor in between the push-button and trigger.

    Connect a 10k pull-up resistor from the switch to +V.
     
  9. zone97

    zone97 New Member

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    There will be no push button. Basically what I wanted to do is connect +v to the +v ground to -V and ground to Trigger. I have a wall timer that will deliver power on the hour for 60 seconds, during that time. The Tm15 circuit will get power and I want it to run for 15 seconds (adjustable by the pot) and then stop. But the ground will be supplied for the whole 60 seconds, and I only want the TM15 to trigger once during that time. While ground is supplied to trigger, it does not function. It expects the trigger to be removed, to start the 15 second timer.
     
  10. KMoffett

    KMoffett Well-Known Member

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    I think this might work, but without the schematic...? Resistor between (+) and trigger, and capacitor between trigger and (-) . This a typical power-on-reset. You may have to play with the R C values.

    Ken
     
  11. Hero999

    Hero999 Banned

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    Here's a schematic.

    It's probably just a 555 anyway.
     

    Attached Files:

  12. zone97

    zone97 New Member

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    I put a 33mf 33v cap between -v and trigger, this does as intended however. It "latches" it doesn't dissipate. I didn't try the resistor to +v because the power is 2amps, and I don't have resistors that big.
     
  13. zone97

    zone97 New Member

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    The circuit doesn't have a 555 on it that I can find, unless its built into the relay?
     
  14. KMoffett

    KMoffett Well-Known Member

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    With the resistor included in my configuration, when you apply power the capacitor is in a discharged state, holding the trigger at (-). The resistor charges the capacitor, pulling the trigger high, allowing the timer to start. When you remove the power the resistor might discharge the capacitor, readying it for the next timer cycle. I would add another like value resistor from +V to -V, to assure this. This all assumes that the timer circuits works that way. But without a schematic, I'm just guessing.

    Ken
     
    Last edited: Feb 7, 2009
  15. Hero999

    Hero999 Banned

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    Well I would have said that 33µF is too large.

    What do you mean?

    I assume you're having problems because there's nothing to discharge the capacitor.

    Don't be silly :D the trigger signal is only a small current. If the power supply voltage is 10V, the resistor is 10k and the capacitor is 1nF, the current will be 1mA decaying to 50µA in only 30µs.
     
  16. zone97

    zone97 New Member

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    The smallest cap, I had was a 1 µf. When I tried your circuit it did nothing. I guess I will have to find a ηf.
     
  17. Hero999

    Hero999 Banned

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    What do you mean it did nothing?

    1µF should work, the value isn't that important.

    Was it an electrolytic or ceramic?
     
  18. zone97

    zone97 New Member

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    It was electrolytic.
     
  19. Hero999

    Hero999 Banned

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    Did you ensure it was connected the right way round?
     
  20. zone97

    zone97 New Member

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    Tried both ways, no go. When i go back to a 33µf It will trip, but not discharge.
     
  21. Hero999

    Hero999 Banned

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    What about 33µF and a 1k resistor?

    The capacitor's positive needs to go to the trigger.
     

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