The sensors and integrated circuit used in this circuit are uncommon today. However, it is worth the configuration for the purpose of consultation.
The circuit is from a June 1995 Electronics Now. The relay is power-dependent and both R1 and R2...
This circuit for several frequencies was obtained in an American documentation from the 90s. The...
The circuit shown in the figure is suggested by AllegroMicro (www.allegromicro.com) and consists of an...