Found in Motorola documentation from the 90's, this circuit has a high input impedance. The power supply must be symmetrical. The circuit can be implemented with modern operational amplifiers.
Found in a 90s nHands On Electronics, this circuit triggers a relay that shuts off the load when...
This project was found in a 1982 publication, using only two transistors. Signal injectors are...
Designed by Philips in 1968 to control the washer water level this circuit uses components from the era....