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555 60s acousto-optic digital timer circuit used in competit

2015-02-03 00:04  
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555 60s acousto-optic digital timer circuit used in competition
The monostable timing circuit is composed of IC1(555) and RP1, R1, C1, the monostable short stabilization time td=1.1(R1+RP1)C1, it is fixed on 60s by adjusting RP1. Pressing AN, the timing is starting. The second signal oscillator is made of IC2 and R2, RP2, C2, the oscillation frequency is f=1.44/(R2+RP2)C2, the frequency can be 1Hz by adjusting RP2. With about 1300Hz frequency, the audio frequency oscillator consists of IC3 and R4, R5, C3, its reset terminal is controlled by IC2's output, when it sends out a second pulse signal, it will emit do sound, LED lights. After timing, IC2's 3 foot turns into low level, then IC3 is in enforced reset state, it stops to vibrate.