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555 used as a delayed pulse generator?

Discussion in 'Electronic Basics' started by Tristar, Aug 23, 2005.

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  1. Tristar

    Tristar Guest

    I'm looking to set us a simple way to turn something on after 10 seconds. The
    resulting output after the end of the 10 seconds needs to be a momentary pulse
    and not stay in a closed position.


    Like this.

    Circuit is started with a momentary contact switch. After 10 seconds (exact time
    isn't critical here +, - a second or two is fine) the circuit momentarily
    outputs a pulse. I thought I'd feed the pulse into a switching transistor to
    make it operate as a momentary contact switch.

    Thanks in advance!

  2. Charles Jean

    Charles Jean Guest


    Here's one that gives about 1 second delay, 1 second pulse. Could
    also use one 556 instead of 2 555s. Delay/pulse is 1.1RC where R is
    the 22K resistors and C is the 47 uF capacitors.
    "Sic hoc legere scis nimium eruditionis habes."
    (If you can read this, you're overeducated.)
  3. This does what I think you want:
  4. Tristar

    Tristar Guest

    This looks easy Terry, I tried Johns circuit on a breadboard last night. I'll
    give this a try too.

    Thanks, Lawrence

    BTW, nice website you have there.
  5. Jasen Betts

    Jasen Betts Guest

    set up the 555 as a monostable and use a capicitor in series with the output
    to pulse the transistor's base when the output changes state after the 10
    seconds have elapsed. (there'll bve a pulse to the transistor when it starts
    too but it'll be the wrong polarity and the transistor will ignore it)
  6. That's what my circuit does.
  7. Tristar

    Tristar Guest

    Hi Terry, It's probably me but I couldn't get it to work, I used a pnp 2N3906.
    I tried various combinations of caps and resistors but no luck.

    Any ideas?

  8. Without more information, not really. Best guess would be that you've
    made a wiring error. As you see from the simulation - the circuit does
    what it's supposed to do.

    How are you testing it? 'Scope, DMM...?

    Is the mono working? If not, then obviously the brief pulse won't be
  9. Tristar

    Tristar Guest

    Hi Terry, I gave it another try and Success this time!

    Thanks again,

  10. Good - thanks for letting us know.

    BTW, *bottom* posting is the favoured standard here.
  11. SARAH


    Oct 19, 2010
    Dear Mr. Terry,

    Kindly precise the transistor used in your circuit, as I tried BC556, and the result was not a pulse, It is remaining high.

    Actually I am trying to have a delayed 3 seconds pulse with 1 second width.

    Best Regards,

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