Push-on/Push-off Switch

August 15, 2013

This circuit was submitted to Broadcast Management and Engineering magazine's Great Idea Contest in 1987 where it was awarded the National First Prize. This circuit was designed at the request of Carl Hanson at KNX-FM and designed by Mike Callaghan, chief engineer of KIIS-FM, Los Angeles.

How it Works
When power is first applied to the circuit, the parallel combination of C1/R2 is charged to 1/2 Vcc through the voltage divider R1/R2. When S1 is closed, C1 discharges through the coil of RL1. This pulls in the relay. The wiper is held in by the current through RL1 and R1.

Any charge remaining on C1 discharges through R2, so when S1 is pressed again, C1 (now a short circuit) releases the relay, returning the circuit to its original condition.

What results is a toggled push-on/push-off action. The momentary switch can originate from another machine or switch closure.

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