This simple Bargraph photometer with 4 LEDs was found in a 1997 documentation. The scale is adjusted in a trimpot and the sensor can be any common LDR. Power can be supplied by cells or battery.
This super regenerative detector circuit was found in an English documentation from 1963. The coil...
This circuit was found in an old English publication. The circuit makes use of general-purpose transistors....
This configuration, which appears in the manual of other manufacturers, is an excellent 1.5 V...