This bidirectional circuit was found in an American documentation from the 80's. The LEDs are common red, and the resistor is calculated according to the formulas next to the diagram.
Found in American documentation from the 1970s, this circuit is intended for amplifying analog TV...
Photoelectric cells can be used as sensitive light sensors. However, the low voltage they generate...
This circuit was found in a 90s American documentation. The circuit uses still common components...