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.
We found this circuit in Radio Electronics Special Projects from 1992. The circuit turns on the...
We found this circuit in the Texas Instruments' Linear Circuits Applications. It uses an...
This capacitive sensor that operates with a high frequency oscillator was found in Radio...