This proximity switch employs a reed switch as the sensor device and the good old CD4017 decade counter for pulse processing. When the circuit is first switched on, the 4017 is reset by the short pulse generated by C2-R3. This results in the Q0 output (pin 3) being pulled high and the LED coming on to indicate standby mode.When a permanent magnet is held in the vicinity of the red switch, the switch closes, generating one clock pulse at pin 14 of the 4017. This is indicated by Q1 (pin 2) going high and relay Re1 being energized via transistor T1.
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