This circuit was found in Sgnetics documentation from the 80's. The circuit also has loudness control. The power supply must be symmetrical.
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...