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.
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
Mouser Electronics has in stock the Texas Instruments TPS7A90 Low Voltage Dropout (LDO) Linear...
This circuit for PC and which can also be used with microcontrollers was found in an English...