Optical potentiometer (CB22159E)

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

Manual Heater Control (CB21276E)
Found in an Electronic Design from the 90's, this circuit uses an SCR according to the controlled power....
Two Transistor Super heterodyne (CB20574E)
This circuit was found in an English publication from 1967. The circuit is for listening on a...
OR Gate with Voltage Comparator (CB19396E)
This is the traditional configuration of an OR gate using a voltage comparator, but it can also be...