This National Semiconductor circuit appears elsewhere on this site. The circuit must be powered by symmetrical source and equivalent modern operational can be used.
With this circuit it is possible to obtain a higher voltage from a zener diode. The circuit is from...
This circuit simply triggers an LED when the sensor is activated. The circuit is from a Popular...
This power supply, found in an Argentine publication from the 1970s, uses a wire potentiometer of 25 W or more...