This circuit was obtained from the Encyclopedia of Electronic Circuits volume 5 of 1995. The circuit uses the 4001 CMOS to obtain hysteresis in the sensor feedback.
Found in a 1966 documentation, this “coin finder” uses components from the era operating at 2.1...
This circuit has an interesting application. If a device with the selector switch in the 110 V...
This circuit uses an unusual Motorola voltage reference. Other manufacturers also provide this...