The PA222 integrated circuit used in this project from an American 1967 documentation is not common today. The circuit can deliver higher power with lower fidelity.
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....