PIC-based Freezer Alarm
Approx construction cost US$14.5
Protect your food from defrosting unexpectedly. Learn about using the 8-pin PIC12C508, and about using the Watchdog Timer.
Some modern freezers contain alarms, which sound if you leave the door open and allow the internal space to warm up. However, they do not work if the freezer suffers a power failure, which is a bit of a drawback. Making a temperature-sensitive circuit that can sound an alarm is not too difficult (a typical example was the Ice Alert project in the Feb 2001 issue), but what is required here is a low-cost circuit that can run on batteries for a very long time.
This design uses a circuit based on a PIC, using a feature about which little has been written, namely the ability to send it to sleep! The circuit is extremely simple, and the software uses several techniques that could be useful in other projects.
More details on this construction project can be found in the May 2002 issue of EPE Online, the world's first web-delivered electronics and computing hobbyist magazine.
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