Found in an old Popular Electronics this circuit can also be adapted to be used as a shield. In this version the control can trigger loads from the light that falls on an LDR.
This circuit is from an English publication from 1979. It describes the assembly of a sensitive touch...
This circuit activates a relay when raindrops fall on the sensor. The circuit is from 1960...
This circuit indicates through LEDs when an automotive fuse is open. ...