SCR photo control (CB8276E)

This circuit is from a 1968 Electronics World. It acts directly on a high voltage alternating current relay. The sensor can be a common LDR.

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Biestable Touch Switch (CB10246E)
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
Battery Charger (CB16778E)
The adjustment of the maximum load voltage is made in the trimpot. The circuit is from 1994...
Differential Amplifier (CIR18634E)
In the figure we have the conventional configuration of a differential amplifier with the...