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Photography by Larry Cotton

TIME-BASED DEVICES

Transplant a heartbeat from cheap alarm clocks.

By Larry Cotton

Some projects need a nice, steady, low-voltage pulse at a constant rate. This is relatively easy to do with the ubiquitous 555 IC, but what’s not so easy is keeping a 555-based circuit accurate to within a few seconds a month. For that, you’re better off just gutting a cheap travel clock. This will give you an easy module that generates ultraaccurate pulses at 1Hz — something which, in my opinion, is more valuable than telling time.

Not just any clock will do, however: it should run on one battery (usually AA size) and have hands, not ...

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