a circuit to switch a relay by a alarm clock

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.

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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. ;-)

Cheers! Rich

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 output?

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 low.

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.

Michael

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 module that was very similar to the modules produced by National in the (what?) late 70's through mid 80's.

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.

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.

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.

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 .

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!

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.

solution

circuit

circuit

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 alarm 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 last 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.

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 :-).

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

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 :)

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

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.

Cheers! Rich

...

Beer. %-}

Cheers! Rich

supplied

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