Found in a 1980s telecommunications documentation, the circuit presented acts as a product detector. The modulator or mixer in the square may be that of the previous circuit.
A touch in this circuit turns-on the lamp or the relay. Power supply is according the lamp or...
Found in a Popular Electronics from the 90's, this circuit uses integrated from that time, today...
This isolated shield for triac was found in old European documentation. The resistor R1, in fact,...