Friday, February 20, 2009

Hacking a digital alarm clock

First of all, this particular hack i did a few weeks ago to make my alarm clock enable external circuits is similar to this one that was featured on hackaday. If you think about building one of them yourself i recommend the other one - it's just a bit more expensive, but much more versatile.

Both basically work the same way: The speaker/buzzer driver of the mobile phone/alarm clock is used to trigger a thyistor. I just used TO92 general purpose transistors i had lying around.
Depending on what kind of signal source you intend to use, you should be able to omit the diode and maybe the capacitors if the resistors are small enough.
Anyway, it's best not to build a discrete thyristor like i did but use a "real" one.
Note that the thyristor will remain latched until you remove the load (e.g. using a switch).

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