wristwatch alarm sound

[marchache]

Good morning,

Wondering if anyone know what is used to generate the familiar (in North America) alarm sound from a digital wristwatch.

I need to recreate this sound, only louder, in a compact form at the push of a button.

I have an old one I'm going to take a part to see if I can modify it but given the simple requirements for the device it is probably easier just to build from scratch.

Thanks
Marc

 

[Johnson777717]

It sounds like...(no pun intended ) the alarm sound is generated by a piezo buzzer (Why they call them buzzers, i dont know, they usually sound more like a beep, although, some are buzzers which sound like a buzz. This would be due to the output frequency of the tone, lower frequency, more buzz, higher frequency, more beep. The package should state the output frequency range.)

Check out piezo buzzers. Radio shack has a few different sizes etc. You can wire one of these up with a switch and you should have a similar sound. If you're looking to pulse the piezo buzzer, similar to an alarm sound from a watch, you can add in a simple 555 timer circuit, where you can adjust the beep-rate. Also, this might allow you to mess around with the sound and intensity that the piezo makes by installing differnent values of capacitors.

The easiest thing to do would be to wire the circuit on a breadboard, which will allow you to mess around with different components etc.
I hope this helps.

 

[marchache]

Thanks. Most piezo's seem to be to too low in the freq range and require higher voltage

I've been meaning to learn how the ubiquitous 555 works. Now's a good a time as ever I guess.

I took apart a dollar store watch today. man they pack the stuff in tight. From what I can tell the chip and speaker sit under the battery.

I'm going to finish pulling it apart tomorrow to see if I can get the speaker out and hook it to the 555.

Marc

 

[Johnson777717]

You're right, piezos usually require a bit of voltage. You speaking of the speaker reminded me that it is possible to create a beep noise using a speaker and a 555 timer circuit. Again, it would depend on the output frequency.

Good luck with the miniature parts. Those things are crammed in there pretty well.

 

[pike]

Just about all watches that have an alarm (piezo) use a piezo material on the back of the watch (which is the metal plate covering the battery. When you apply voltage, it warps one way, if you switch the piezo terminals around, it warps the other way.

The only way to make it louder would be to apply more voltage to the circuit. This isn't gonna be easy trying to modify a watch ..

 

[marchache]

watch alarm

FYI. Took another tack. Watches were way too small and not loud enough to work with so I raided the $1 store again and picked in a small alarm clock (with hands).

Took it apart, removed all the gears (kept 'em for small robot projects) and was left with the beeper circuit, the piezo (very small about 1/2 diameter) and battery. Voila ! Just what I needed.

Also a coil in there that seems to drive the main gear. Have to explore that a bit more.

Marc