Darkness Monitor (CB21019E)

Found in Popular Electronics this circuit triggers an SCR and lights an LED when the location of the sensor is dark.

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Two conventional 78xx power supplies (CB25958E)
This circuit appeared in the June 1990 issue of Radio Electronics magazine. Integrated circuits must...
SCR Photosensor (CB16109E)
Lockout shooting, due to the incidence of light, can be achieved with the circuit in the figure. In...
Galena with FET Preamplifier (CB10212E)
This circuit can function either as a crystal or galena receiver with a pre-amplifier using a FET...