This circuit was found in a Radio Electronics from 1970. The coupler with LDR is from that time, but the circuit can be adapted to use modern components and act as a shield.
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...
This circuit is from an Electronics Now from August 1995. The triac is according to the load that...
This circuit is from a Hands-On Electronics from the 90s. The integrated amplifiers used are well...