Optical potentiometer (CB22159E)

This voltage-controlled potentiometer using an LDR was found in an English documentation. LDR is common and LED of any type.

Clef Generator (CB827E)
This circuit produces a clef sound when a pulse is applied to its input. The damping effect is...
Microphone Amplifier (CB14330E)
This circuit can serve as the basis for a simple phone. The LM10 is not common today, but the...
Optical Link Receiver (CB4945E)
This is a possible circuit for the receiver of the previous circuit. Other circuits can be found...