This automotive circuit was found in the September 1992 issue of Radio Electronics magazine. The circuit directly drives a relay that must have a coil resistance greater than 65 ohms.
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...