Super Alarm Clock

[Xyver]

Today, my friend asked me if I could make a super alarm clock for him.  The basic idea is take an alarm clock, and attach 3 strobe lights and a siren to go off when the alarm goes off. I thought all you had to do was open the alarm clock, de-solder the alarm, and attach the other things instead.  But, I realize that won't work, because each strobe light is 12 volts, and I'm 99% sure that a little alarm clock doesnt output that kind of power.  So my idea was have a seperate power supply for the extras, then just attach a transistor to the alarm , so that when the alarm goes off it opens the transistor and allows power to the lights?  Would that work?

[Hawaii00000]

As far as I know a transistor can't handle 12v, so you'll also need a relay.
When the transistor is activated, it will activate the relay which will activate the strobe lights.
You can buy relays at Radio Shack in the US or Dick Smith is Australia or you could just order online.

[madsci1016]

relays may fry the alarm clock if the clock's alarm driver can't handle the current load.

You need to take the alarm clock apart and see what you have to work with. The alarm could just be a speaker, and attaching a relay or transistor to a speaker leads won't work.

[Soeren]

Hi,

As far as I know a transistor can't handle 12v, [...]

That shouldn't be a problem, you can get transistors handling more than 1kV.

[Soeren]

Hi,

Today, my friend asked me if I could make a super alarm clock for him.  The basic idea is take an alarm clock, and attach 3 strobe lights and a siren to go off when the alarm goes off.

Super?
My idea of "Super" in that sense, is a clock that wakes you up as softly as possible.
Waking up to a siren and strobes are bound to ruin his day.

The smart way to wake up is a slowly increasing lamp with a regular alarm clock as a "back catcher"... And about 8 hours of sleep 
Strobes and sirens indicate much too little sleep and combining lack of sleep with a chaotic wake up will take its toll on your friend - As a good friend, convince him to sleep more - he'll be much happier and think better if he does!

I thought all you had to do was open the alarm clock, de-solder the alarm, and attach the other things instead.

Don't desolder the alarm. Find out if the buzzer is a piezo or a regular buzzer and I'll draw you a circuit to tap into that.
It's probably best to use a monoflop after the initial "tap circuit" and let the mono drive the rest. Whether a relay is needed or not depends on the current drawn from the strobes and siren, so measure that (they may have ratings printed on somewhere, but that will be generalized max. specs. so better measure what's needed.
And yes, you will need to use an external supply. Some alarm clocks run on a single AG13 button cell or an AAA cell, so wont' be able to supply anything useable.

If your friends alarm clock is generally loud enough for normal use, maybe he ruined his hearing in that frequency band (by sleeping next to a blasting clock perhaps ) and need a lower frequency to get the full sound perception.

[Xyver]

Haha well he called me this morning, and asked if I could make him a "super alarm clock" (his words), and then told me his plan, and asked me if i could do it.  So I said I'd look into it.  Totally his idea, not mine.  He had just woken me up, I was half conscious and in no state of mind to think of anything "super". Ill try and get the pieces, and see what I have to work with.  I'll do some probing with a multimeter, and see what voltages and amps everything is.