This old version of analogue switch was found in a 1969 documentation. Components of the time are used, with emphasis on the CAG7 integrated circuit. It is worth as a reference.
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....