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.
The circuit presented, from 2006, serves to control loads at a distance, robots, etc. It can be...
This circuit is given in two versions, having been found in a publication from the 90s. The second...
I found this circuit in a documentation for radio amateurs from 1975. The FET could be the BF245....