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Looking for simple 555 relay circuit

Discussion in 'Electronic Basics' started by ZhangLu, May 24, 2004.

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  1. ZhangLu

    ZhangLu Guest

    Hi all,

    Looking for a circuit diagram (on trip board) that utilizes ic 555, using
    12V AC power input that:

    On when pressing a switch
    Off when pressing the same switch
    Beeps every 10 sec.
    Drives a 12V 55W light (AC or DC)

    Can anyone help?

    New learner
  2. JeffM

    JeffM Guest

    New learner (ZhangLu) asks:
    Easy so far.
    Not a problem.
    How long does it beep?
    Be much more specific: When does it light; when does it go dark?

    In the future, basic questions should remain in sci.electronics.basics.
  3. My guess would be say 500mS. So an astable with appropriate duty cycle
    would drive it. And it could be gated by a flip-flop, triggered by
    momentary switch contact.

    But what device is to be used for the beep? A DC buzzer? If it's a
    miniature loudspeaker, a further circuit section is needed to provide
    the oscillator. At what frequency?
    Fair point - I suppose I'd have assumed it would light simultaneously
    with the beep. IOW, a Beep & Flash alarm of some sort. But it would be
    good not to have to guess <g>.

    How important is it that it to use a 555? At first sight I'd have
    thought it easier to implement with CMOS 4001/4011. The light
    requirement means a relay is needed anyway, so one major merit of 555
    - its 200mA direct output drive current - is of no consequence. And
    although you can make a F/F (bistable, or 'toggle') with a 555, it's
    more usual to use a couple of logic gates.

    BTW, I take it this is not homework?
  4. ZhangLu

    ZhangLu Guest

    Thanks for your reply.

    The bulb will light on when the switch is pressed once, and the DC bleeper
    will beep every 10 sec simultaneously as a 10 sec counter until the same
    switch is pressed again to stop both the light and bleeper.
  5. ZhangLu

    ZhangLu Guest

    Thanks Terry.

    I'm a new hobbyist trying to play with 555. If you think CMOS 4001/4011 can
    do the trick better, are you able to suggest a circuit for me to work on?
  6. Soeren

    Soeren Guest

    Hi Terry,

    I assume from this:
    "On when pressing a switch
    Off when pressing the same switch"

    That the lamp should be considered the output (on = light and vv.)

    The next part: "Beeps every 10 sec." I see as something independant of
    the switching ?

    Something _similar_ to a manualy controlled photographic enlarger with
    beeps to mentally count off the interval at hand ?
  7. By 'switch', I assume you mean a momentary contact push-button? As I
    said earlier, that will require a simple flip/flop (toggle) followed
    by a gated astable.

    But must you use a push-button? If you used a simple SPST switch
    instead, then you could eliminate the toggle. You would switch control
    directly to the lamp circuit, and off again (a relay, switching higher
    power to the lamp). And that same signal would gate the astable, which
    would drive the DC beeper.

    If it *does* have to be a push-button, please confirm that this is the
    intended timing diagram.
  8. ZhangLu

    ZhangLu Guest

    G'day Terry,

    Thanks for the diagram, that's exactly the timing I intended to have. The
    switch is a momentary contact push-button.

    New Learner, Malaysia
  9. Soeren

    Soeren Guest

    Hi ZhangLu,

    Thought so :) But what precision do you need in the timing of the 10
    second intervals ?

    If demands are not too strict on timing, it could be build with...
    1 CD4093, 3 transistors, a couple of diodes, a few caps, ~12 resistors, a
    small (32 Ohm?) speaker, a relay and the pushbutton.


    * If it puzzles you dear... Reverse engineer *
    New forum: <URL:>
  10. OK, here's a circuit to do it. It contains full notes, so should be
    self-explanatory, but post again if not clear. Breadboarded and works

    Many alternative designs are possible. And you could use a relay for
    driving the high power lamp if you have a suitable one to hand,
    instead of the power MOSFET I've recommended.
  11. Far fewer than that <g>. See

    What were you proposing to use around 12 resistors for?
  12. [etc]

    One point I forgot to mention. C2 must not be a polarised type. In
    this case I connected a pair of identical 10uF electrolytics in
    series, back to back (-ve ends together). That effectively gives a 5uF
    non-polarised equivalent.

    | + ---
    ### 10uF |
    --- |
    | |
    | | = 5uF
    --- |
    ### 10uF |
    | + |
  13. Soeren

    Soeren Guest

    Hi Terry,

    Well, that _won't_ work, so you get a (free) extra try ;)

    Making it work ;) (with bipolars, including one used as inverter), with
    10 sec. period adjustable +/- ~2.5sec and generator for the beep sound
    into a speaker.



    * If it puzzles you dear... Reverse engineer *
    New forum: <URL:>
  14. Fred Bloggs

    Fred Bloggs Guest

  15. ZhangLu

    ZhangLu Guest

    Thanks everybody!! I've learned a lot from all of you.

    BTW Terry, may I assume that this circuit works on 12V DC and the
    +ve input is around C3?

    I intend to use a heavy duty relay to replace Q1 MOSFET to drive the 55W

    Again, thank you so much.

    ZhangLu, New Learner
  16. As I said, "Breadboarded and works fine." Would you like to see a
    screenshot of its output? And it simulated OK too. There's always the
    possibility that I've drawn a different circuit to the one I simulated
    and built, but at a quick check that doesn't appear to be the case.
    What are your problems with it?
  17. Agreed, but I hardly think that matters in this application, do you?
    One press of the button, if necessary, if he wants to 'start' with
    light and beeping OFF.
    Ah - I now see I *have* drawn it incorrectly, sorry! U2Cpin8, C2, R3
    and D1 share a common node, but do *not* go to Vdd, as you rightly
    point out, thanks.
  18. Obviously *too* quick! Fred's post prompted a closer look and I've now
    corrected that silly drawing error. Any more problems with this
    working circuit?
  19. Yes, it works fine at 12V. I assume you have the corrected schematic?

    Pins 14 and 7 of the 4011 (or 4093) go to 12V an 0V respectively.

    OK. Instead of wiring to the gate of MOSFET Q1, use a simple relay
    driving section like that in Soeren's circuit.
  20. Soeren

    Soeren Guest

    Hi Terry,

    Yup :)

    I guess you are one of the build-first-make-drawings-later kind of guys ?
    Even if you are, build after the schematic when it is finished, or better,
    let somebody else build it up, it will catch all these drawn-late-in-the-
    night errors :)

    Not except that you cannot adjust the timing and you have to use a buzzer
    instead of a cheaper "loose" piezo disk ;)

    (Just teasing you know :)


    * If it puzzles you dear... Reverse engineer *
    New forum: <URL:>
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