Found in a 1980s documentation, this circuit uses as base a component of the era. The formula for determining the conversion is given next to the diagram.
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....