Optical potentiometer (CB22159E)

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

Indicator for Christmas tree (CB20942E)
We found this circuit in a Popular Electronics from the 80s. The circuit is based on the LM3909, a low...
AC Gain 10 Amplifier LM3900 (CB19120E)
In the figure we have the basic configuration of an operational amplifier for AC signals using the...
Timer with Relay 14538B (CB18466E)
This timer, like the previous circuits, uses a currently uncommon integrated circuit. The time is...