Found in a Hands On Electronics from the 80's, this circuit activates a relay with alternating touches on the push-button. The relay depends on the supply voltage.
This fast trigger circuit allows the counting of up to 300 pulses per minute. The circuit is from...
This intercom uses transistors from the 60s. It was found in a Japanese publication at the time....
This circuit is from an old publication from the 90s, but it can be adapted to operate with LEDs....