1 Minute Time Delay using a 555 Timer

Discussion in 'General Electronics Chat' started by pauliewalnuts, Apr 19, 2008.

  1. pauliewalnuts

    pauliewalnuts Thread Starter New Member

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    Hi,
    I need to create a delay of 1 minute using a 555 Timer. The Timer will receive an input from a relay contact (this is not a constant supply), then wait for 1 minute before giving a one shot output.
    Is this an easy circuit to build? I have come across plenty of timer circuits that will give an output FOR a set time, I need the circuit to WAIT for 1 minute then give the output.
    Many thanks for any help.
  2. beenthere

    beenthere Retired Moderator

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    How long is the one shot period and what polarity must it be?
  3. pauliewalnuts

    pauliewalnuts Thread Starter New Member

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    The one shot is just a positve feed to a PLC, the timer only has to give an output for approx 1 sec.
  4. beenthere

    beenthere Retired Moderator

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    You will need two 555's (or a 556). The first will go active for 1 minute from the relay contact, and will trigger the second when it times out.
  5. pauliewalnuts

    pauliewalnuts Thread Starter New Member

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    Thanks, Im a bit of a novice when it comes to 555 timers. I have heard of a 556 though. Would you mind explaining a little more about the reason for needing two 555's - when you say the first will go active for 1 minute, then trigger the second.
    Thanks a lot.
  6. beenthere

    beenthere Retired Moderator

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    When a device is triggered, the output state changes. So a single 555 won't do for your needs. The idea of using two of them is that the first one can trigger the second one. The first gives the 1 minute delay and the second gives the 1 second output pulse.

    I'm pretty sure that an LM556 is a dual 555. At any rate, get the data sheet for both.

    I'm off to bed, try to be more useful tomorrow.
  7. pauliewalnuts

    pauliewalnuts Thread Starter New Member

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    So are you saying that the first will give an output FOR 1 minute, and the second wont do anything until the output from the first 555 goes low.
    So the first 555 will immediatley give an output once the relay contact goes high (for 1 minute), and the second will give an output for 1 sec AFTER 1 minute has passed?
    Sorry for being a bit of a thicko here but your really helping me out. Many thanks again.
  8. KMoffett

    KMoffett Senior Member

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  9. mik3

    mik3 Senior Member

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    If you want you can you use one 555 and a transistor to invert its output. But why dont you use the PLC itself to make the 1 minute delay?
  10. SgtWookie

    SgtWookie Expert

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    See the attached schematic. Times are approximate, of course - your mileage may vary. You can use two 555 ICs, or a single 556.

    Attached Files:

  11. robby991

    robby991 Active Member

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    Sgtwookie. I implemented your schematic to see if I can generate a delayed pulse but it it not working correctly. I changed the resistor and capacitor values to customize my delay though. I first checked the first 555 to see if it was working correctly and it was. I pulled the input high with a resistor then triggered a negative pulse then scoped the output of it. The output produced a pulse of RC width like it should. Next I scoped the output of the second 555 to see if it was generating a delayed pulse but it was not. It just remained flatlined at 0 volts. There is a problem with the 2 555 linked together but I cannot figure it out. What will typically cause this to happen? The falling edge of the first 555 pulse should trigger the second, correct? Should I be adding anything to this circuit?????
  12. flubbo

    flubbo Member

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  13. baseball07

    baseball07 Active Member

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    I am still confused as to how the first 555 triggers the second. The second 555 is pulled high, which means it needs to get pulled below 1/3 V+ for it to trigger. Now the first 555's output is just a pulse with duration RC. How does the first 555 falling edge pull the seconds input down? I would think that the input to the second 555 remains high as the output of the first goes up then comes back down. I feel like there needs to be something else that actually pulls the input to the second 555 down. How does this work?
  14. st_bonifface

    st_bonifface New Member

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    hello there if any one know how to build a power regulator with a 555 timer as a power on delay?
    Please help me!!!
    thank you wry much
  15. italo

    italo New Member

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    you don't need two LM555 only one use a transistor on the output to provide polarity switch trigger pin 2 through a cap pulled up to vcc. I will not go into the timing plenty of info on that.
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