How can I delay 2 relays?

Discussion in 'The Projects Forum' started by Franco_oz, Jan 12, 2009.

  1. Franco_oz

    Thread Starter Active Member

    Jan 12, 2009
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    0
    Hi Guys, I am trying to build a circuit to drive 2 relays using just one push button. When the button is pressed, i need the first relay to come on for about 7 seconds and then energize the second relay for about 4 seconds.
    I am trying to start a diesel genset using just one control line and the first relay is used to energize the glow plugs while the second relay provide the cranking. I tried few ideas based on RC circuitry to drive CMOS gates (old 4000 series) but didn't get much luck. I know a little bit of electronic but obviously not enough to solve this (quite simple?) problem.
    I understand it is very easy using a pic but am not skilled to use it. Anyone willing to point me to right direction?
    Thanks. Franco :(
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can use two 555 or a 556 (two 555 on a single chip) timer ICs to produce the delays. The first 555 will be energized by the push button and the second by the first relay contacts.
    Look here for a delay circuit with a 555 which is called monostable:

    http://www.eleinmec.com/article.asp?4
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Do you want the grow plug relay remains energised while the engine is in the "4 seconds cranking" state?
     
  4. Franco_oz

    Thread Starter Active Member

    Jan 12, 2009
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    At the key switch glow plugs are ON during cranking but it is not important. In my experiment i didn't and engine start ok. Franco
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The simulation use 2 separate 555 but you can use a 556 instead.

    Both 555 is wired up as monostable and all their outputs are low normally. The first 555 is set to timeout after 11 seconds while the second 555 set for 7 seconds.

    The cranking switch SW should be momentary and would start the cranking process automatically after a brief closure.

    Check carefully the back emf diode polarity during soldering.

    [​IMG]
     
  6. Franco_oz

    Thread Starter Active Member

    Jan 12, 2009
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    0
    Thanks, guys, it works! Franco
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
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