Found in Popular Electronics from the 90s, this circuit can be used in tachometers. The integrated circuit is not a common component today.
This dual flasher for high brightness LEDs was found in an American documentation from the 90's....
In the figure we show how to polarize a phototransistor to obtain sensitivity. The circuit is from...
This circuit for igniting gas flames was found in a 1967 Electronic Design. The SCR firing device is a...