Receiver for FM Infrared Audio Link (CB20978E)

This circuit was found in a Popular Electronics from the 90s. The components admit equivalents and the phototransistor can be of any type.

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Light Controlled Power Switch (CB12286E)
In this circuit of a 1991 publication, we can use the 2N2646 unijunction transistor and the sensor...
General Purpose Meter (CB23574E)
Measuring capacitances and resistance this simple instrument was found in Radio Electronics...
Metal detector (CB7959E)
Found in a 90’s 303 Circuits, this circuit uses components that are still common and has a common...