FREQUENCY_BASED_LOCK

Published:2009/6/19 1:38:00 Author:May | From:SeekIC

The system is formed by two separate circuits-a key and a keyhole. The key engages the key-hole with a mating pair of connectors. The key is a tone-generator circuit consisting of a 4049 hex in-verter CMOS IC (U1), switches (S1 and S2), a resistor (R1), and a capacitor (C1). The value of the tone generated by that circuit in Hz is determined by;The keyhole is a 567 tone-decoder circuit that can be conftgured to detect any frequency from 0.01 Hz to 500 kHz. The frequency it detects (fo), via the 567 IC, turns on the relay (K1). Compo-nents R3 and D1 are used to latch the circuit, so the output stays on even after the input tone is re-moved. When S2 is pressed, the system is reset. Switch S3 resets the circuit from inside.



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