Posted on Aug 25, 2012

This pseudorandom sequencer drives a solid-state relay. If you power a low-wattage lamp from the relay, the lamp will appear to flicker like a candle`s flame in the wind; using higher-wattage lamps allows you to simulate the blaze of a fireplace or campfire. You can enhance the effect by using three or more such circuits to power an array of lamps.

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The circuit is comprised of an oscillator IC1 and a 15-stage, pseudorandom sequencer, IC2 through IC4. The sequencer produces a serial bit stream that repeats only every 32, 767 bits. Feedback from the sequencer"s stages 14 and 15 go through IC4D and back to the serial input of IC2. Note the rc network feeding IC4C; the network feeds a positive pulse into the sequencer to ensure that it won"t get stuck with all zeros at power-up. The leftover XOR gates IC4A and IC4B further scramble the pattern. The serial stream from IC4B drives a solid-state relay that features zero-voltage switching and can handle loads as high as 1 A at 12 to 280 Vac.

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