Found in a Popular Electronics from the 90's, this circuit detects the approach of objects by the reflection of the radiation emitted by the LED. The relay is a 12 V sensitive type.
This circuit, from the 1977 GE semiconductor manual, uses a unijunction transistor beyond the...
This circuit, when connected to the 110 V power grid makes it possible to test capacitors with...
This circuit was found in a Texas Instruments handbook about operational amplifier. It has a very...