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a circuit to switch a relay by a alarm clock

Discussion in 'Electronic Basics' started by Thomas Vogel, Apr 5, 2005.

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  1. Thomas Vogel

    Thomas Vogel Guest

    I want to construct a circuit which switch a relay by a alarm clock.
    Know anyone where I can find a plan in the internet or in a book or in
    a magazine?

  2. Lord Garth

    Lord Garth Guest

    You must define what signal the alarm clock produces before you can
    get any useful responses. What is the output voltage? Is it a pulse or
    a level? What are the specs of the relay you wish to use? Is the relay
    supposed to stay energized until it is manually reset? Is the relay circuit
    powered by a battery or a line source?

    Perhaps you mean you wish to build a digital alarm clock with a relay
  3. It sounds to me like he wants someone to explain how to do it, the problem
    being that the chances of two people having the same clock radio is pretty

    I did it to one, but it was really simple because I used a clock radio
    that was fairly old, and the clock was on a separate board from the actual
    radio. That made it real simple to find the wire that turned on the
    radio, and use it to turn on a relay.

    Not that it's that much more difficult in more recent clock radios,
    just that it's jammed into a smaller space. The obvious thing is to
    take a clock radio that's cheap, open it up and then find the datasheet
    for the clock IC. That should give information about the "alarm" output.

    Of course, given the tone of the original question, it might just be
    simpler to rectify the audio from the radio, easily found since it's
    available on the speaker terminals, and then amplify that up enough
    to feed a relay.

    Forest Mims did something like this one, using an SCR to detect the
    signal intended for a piezo speaker in a battery timer, which then
    could turn on something more. Of course, it latched, being an SCR,
    so the output was turned on even after the "alarm tone" ended.

  4. Why not just buy a timer? You can get them with plug outputs, that can
    be set just like an alarm clock, or even set with ranges, so the plug
    turns on at say 9pm, and turns off at 6am.

    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
  5. Lord Garth

    Lord Garth Guest

    We'll see if he ever gets back to the group...

    I took apart a Garfield alarm clock last year and found it had a clock
    that was very similar to the modules produced by National in the (what?)
    late 70's through mid 80's.
  6. Rich Grise

    Rich Grise Guest


    I did this once with a "modern" digital alarm clock with a piezo beeper.
    I just picked off the pulses to the beeper, and triggered a retriggerable
    one-shot to turn on my large alarm, which was just a MVB and big speaker.
    Actually, it was two MVBs, so I got a two-tone blare that really annoyed
    the neighbors. ;-)

  7. Lord Garth

    Lord Garth Guest

    Geez! I never needed such noise to awaken! What the heck knocked you out
    so hard? The ticking of a mechanical clock keeps me awake.
  8. Is it possible that the OP wants to use an old-fashioned mechanical
    alarm clock as the source? If so, that gives me an excuse for some
    nostalgic recollections <g>.

    About 20 years ago, chatting to a friend in the office about our
    shared habit of early rising, he mentioned that he had to wake his
    deaf teenage daughter each morning. She too had to leave early for
    work but because of her handicap couldn't use normal alarms like a
    clock or radio. That got me exploring some electronic possibilities:

    Light - simulating the sun beaming down onto her face. A bright
    spotlamp perhaps, or an infra-red lamp of the sort sometimes fitted in
    bathrooms. Quickly dismissed as I didn't know enough to be sure of its
    safety over prolonged exposure. I did try a few experiments with
    flashing a normal domestic 100W spotlamp a couple of feet away but
    decided that couldn't be reliably expected to wake her up, even if she
    happened to be facing directly towards it.

    Breeze - a pleasant stream of air from a bedside fan. Experiment
    quickly showed it would need to be a largish fan to have any chance.
    But impossible to devise a reliable way of ensuring it stayed in
    position, short of strapping it to her head!

    Electric Shock - fleetingly toyed with the idea of a (battery
    operated!) wrist strap, delivering a 40 or 50V. Really was fleeting

    Vibration - finally settled on this, and built a gadget which she used
    successfully for many months.

    A small d.c motor with a lead weight attached eccentrically vibrated
    sufficiently when placed under the pillow. Used an old, cheap
    mechanical alarm clock with a modification to the striker mechanism so
    that it repeatedly opened and closed an electric contact.

    The clock was mounted on top of a home made wooden box, and the
    ultra-simple electronics on a piece of stripboard. A jack plug and
    socket were used to connect the circuit's output signal to the motor
    unit via a pair of wires about a metre long. An l.e.d in parallel with
    the socket provided a supplementary indication, useful for testing.
    Improvised electrical contacts by epoxy gluing a strip of tin inside
    the casing, isolated electrically by the glue, so that the hammer
    could strike it without hindrance. While the contacts were closed, a
    brief positive pulse was delivered to the base of a darlington pair
    arranged as an emitter follower. If the plug was in place, then the
    motor vibrated. In any case the l.e.d would light. With 3 x 1.5V
    D-type batteries, after allowing for the two base-emitter drops this
    delivered a little under 3V to the motor. Quiescent current was
    negligible, so no additional ON/OFF switch was necessary in practice.
    The existing mechanical one on the clock served the purpose. The
    motor was mounted in a small plastic case. Finished unit:

    I was pleased to hear that it performed very well in practice. But
    about six months later it got dropped from a shelf, disintegrating
    beyond repair. At least, that's what my friend told me!
  9. Lord Garth

    Lord Garth Guest

    I think he was a troll Terry, there has been no return of the OP to the
    group for any clairification.

    I had a deaf person sleeping on my couch one weekend, she
    slept so soundly that even a wet cloth on her face did not rouse her.
    I hope she never has to contend with a fire. BTW, I'm told that her
    dog would lick her hand at the sound of the alarm to awaken her
    however the dog was not here. Using animals to wake her is about
    the best solution I could imagine.

  10. Thomas Vogel

    Thomas Vogel Guest

    the alarm clock produce a signal which changes all the time. It goes
    with a 1,5V battery, so the output is by ~1V.
    The relay is powered by a battery.
  11. Thomas Vogel

    Thomas Vogel Guest

    the alarm clock produce a signal which changes all the time. It goes
    with a 1,5V battery, so the output is by ~1V.
    The relay is powered by a battery.
  12. Lord Garth

    Lord Garth Guest

  13. Lord Garth

    Lord Garth Guest

    You will need another power supply because that 1.5V battery is insufficient
    for the new circuitry.

    You say the signal changes all the time, I presume this means you are seeing
    an oscillating alarm output which is probably meant to be buffered and then
    drive a piezo speaker. There is the possibility that you are saying the
    output changes as the clock battery ages however.

    With such a low output voltage, you will need to amplify the output before
    you can do anything useful.

    The likely relay driver would first amplify the alarm output then use this
    to trigger a one shot, to rid your alarm signal of the oscillations. The
    step is to use the one shot output to activate the relay.

    There are several approaches to a solution, however, I would suggest you
    move this discussion to alt.binaries.schematics.electronic so that actual
    pictures and diagrams can be attached. ASCII art is rather crude.
  14. Light - simulating the sun beaming down onto her face. A bright
    Actually this works great for me. A floor lamp with a timer that turns
    on about 15 or 20 minutes before I want to get up convinces my
    subconcious that the sun has been up for a while :).
    --email: icbm: Delray Beach, FL |
    <URL:> Free Software and Politics <<==+
  15. Lord Garth

    Lord Garth Guest

    ....and if you're a gecko, so much the better!!!
  16. GotCoffee

    GotCoffee Guest

    How about using the timer on an automatic coffee pot. The power
    supplied to the heating element can be used. If hooked up properly,
    you can get woke up a hot cup of coffee :)
  17. Lord Garth

    Lord Garth Guest

    YEOW!!!!!! Wouldn't you rather be awakened by the SMELL of
    a freshly perked pot of coffee? :)
  18. Rich Grise

    Rich Grise Guest

    Yeah, and set up a hot plate with some bacon, to get that nice aroma! This
    would need a cutoff timer, of course, so it doesn't burn.

  19. Rich Grise

    Rich Grise Guest

    Beer. %-}

  20. Lord Garth

    Lord Garth Guest

    Mmmm, night old unrefrigerated bacon!!!! See you in the *burpppp!* doctors
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