This 1980s circuit was found in Motorola documentation. The circuit uses period components that admit of equivalents. Light feedback in a modern version can be done by optical fiber.
Indicated to be used at the sensor input of a PC, this circuit was found in an English...
This 80's circuit, suggested in Texas Insrtruments documentation, uses a Hall effect sensor. The...
Found in a 1991 Hobbyst Handbook, this circuit monitors both battery and alternator voltage. The set...