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555 timer circuit

Discussion in 'Electronic Design' started by John Winstead, May 13, 2005.

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  1. I'm trying to build a 555 or 556 timer circuit that creates a 5 second pulse
    to activate a small reed relay every 5 or 6 minutes. Can anyone help me
    with that. Thank You.
  2. OBones

    OBones Guest

    So you want it to work in astable mode with Tl = 5min and Th = 5s

    It's not that hard, read the datasheets.
  3. Graham Orme

    Graham Orme Guest

    You'll have trouble getting a 555 to run that slowly. You'd have to use
    a very low charging current for the capacitor, and it may be less than
    the capacitor's leakage current.

    I'd use a 4060 ( ) to
    produce a pulse every 5 or 6 minutes then use that to trigger a 5
    second monostable. I seem to recollect that the 555 can be used as a
    monostable and 5 seconds would be do-able.
  4. Ken Smith

    Ken Smith Guest

    If you can live with the nominal 5 seconds VS 5 minutes ratio being
    fixed you don't even need the 555:

    Q(N) ---/\/\/-----+------------- Reset
    Q(N+A) -------------+-------------- Pulse

    Q(N) needs to be such that it has a period of 10 seconds so that it will
    be low for 5 seconds after Q(N+A) goes high.

    From the reset, it will be 10 seconds times 2^A until Q(N+A) goes high.
    It will then remian high for 5 seconds. If you make A 5, the full cycle
    will take 325 seconds.
  5. John Fields

    John Fields Guest

    A 555 (even a CMOS 555) is kind of iffy at 5 minutes, so you might
    want to try this instead:

    | Vcc | | | +V
    [510K] | +-->[250k] [0.1µF] |
    | [100K] | | HC4060 +-------+
    | | +-------+------+------+ |K | O----->C
    +-------|Rs Rtc Ctc | [1N4148] [COIL]- - -|
    | | | | | O--> |
    +--|MR Q7 Q13 | +-------+ |
    | +------------+----+---+ | +---------->NO
    | | | C
    +---[1N4148>]---+ +--[510]--B 2N4401
    | | E
    +---[1N4148>]--------+ |

    Set the pot to 160K and the output pulse will be about 5 seconds long
    with a time between pulses of about 5 minutes and 20 seconds.
  6. See my reply in sci.electronics.basics, pointing you to this solution:
  7. Ken Smith

    Ken Smith Guest

    A slight change:
    You don't need two diodes.
  8. John Fields

    John Fields Guest

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