Posted on Feb 5, 2014

Controls intervals up to 1 h in 1-s increments as programmed by thumb wheel switches S1 and S2. Circuit is basically two-stage programmed counter driven by 1-s clock derived from 60-Hz power line. A1 is connected as divide-by-60 counter triggered by 60-Hz signal developed across D2. 1-Hz output from A1 triggers A2 which in tum triggers A3, all pro

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grammable timers. When S3 is closed, R4 bus goes low to start timing cycle. Relay driver A4 holds relay K1 closed for application of AC power to device being controlled and energizing of LED to indicate active timing cycle. Applications include uses as kitchen and darkroom timers, -W. G. Jung, "IC Timer Cookbook, " Howard W. Sams, Indianapolis, IN, 1977, p 214-218.

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