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.
Here is a simple source without a transformer for currents up to 50 mA. The voltage depends on the...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This circuit drive an LED with constant current determined by the values of the resistors of 10...