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 that can only be used with simple resistive and inductive loads (never electronic) was...
This digital instrument input circuit was found in the September 1989 issue of Radio Electronics...
This circuit was found in an 80s documentation. The integrated circuit used is from that time,...