Re: a circuit to switch a relay by a alarm clock


"Lord Garth" (LGarth@xxxxxxxxxxxx) writes:
> "Thomas Vogel" <Tommi-Vogel@xxxxxx> wrote in message
> news:7f88d87.0504050839.7cbf63a1@xxxxxxxxxxxxxxxxxxxxx
>> 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?
>>
>> tommi
>
> 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 data***
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

.