Hacking An Alarm Clock

My sister (yes, the one for whom I made earrings) wants me to modify an alarm clock to run a small electronic device when it goes off. Preliminary research has given me two methods:
1) A digital clock with a 555 timer circuit
In this setup, a 555 timer circuit is used to translate the signal to an alarm speaker/piezo disk into a relay. When the clock goes off, the relay clicks, and any electrical device that is run through the relay has power.

2) An analog clock with a transistor amplifier
In this version, the analog clock seems to just have a straight DC output to the alarm. The transistor is used to amplify the DC to drive the motor of a fire bell.

Which of these would be easier to implement? The device I am supposed to use runs off of 3VDC, so I was just going to run the power line through the relay or through the transformer.

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randofo9 years ago
I did something like this once. I used an AQV210EH low-voltage relay (which from my understanding is just an opto-isolator). You need to be careful with these since they are static sensitive and crossing the pins with your fingers could short the chip. If the doesn't work quite right, try adding a low-voltage regulator coming from the alarm. This will create an even voltage from the alarm signal which will more consistently trigger the relay. Also, go to youtube and type in "watergun alarm clock"
CameronSS (author)  randofo9 years ago
I just found a PC817 on an old fax machine board...would that work?
There's a chance... try it with a AA battery and see if you could turn on and off an LED (with a different power source).
CameronSS (author)  randofo9 years ago
I'm pretty sure I understand how it works, but where would I find one of these relays? Does Ripoff Shack carry something similar? Or do I have to special-order one?

However, as tech-king pointed out... it probably can easily be solved with a switching transistor which you should be able to find at Radioshack.

Or other things to try If you want to go the Radioshack route:

You can probably get a variable voltage regulator at radioshack (1.5 - 18V) and hook that up the alarm at a reasonable setting for an LED. Then have the regulator power on and LED when the alarm goes.

You then need to have the LED pointed at a photocell hooked up to a 741 chip. See this for a schematic:


And then have the 741 hit a 5V relay...

Or perhaps you could hook the 741 directly to the alarm. I've never tried this. You should try that since it will most likely work. Try setting up the alarm to trigger the 741. That should work. You still might need to put a voltage regulator in-between or something of the sort to increase and stabalize the voltage from the alarm output. I'm not sure what you can get at Radioshack to do that...
i checked out the firebell one; its needlessly complex. its uses a pnp attached to a battery to negatively bias itself and go on with the alarm, and also switches on the alarm, which needs a separate power supply. needlessly complicated and archaic. here is a simpler circuit, thats powered off a 9 volt battery.
fireball one?
i wrote firebell. although spell check does want me to put fireball. or do you mean it should launch fireballs in time to the alarm?
Maybe it was wishful thinking
damn it, forgot image
pilot alarm.bmp
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