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.
In the figure we have an increased dynamic response configuration with the use of a transistor (TR3) in...
This tuned circuit was found in a 1966 Electronic Circuit Handbook. The transistor can be any...
This transmitter for the 40 meter or 7 MHz band was found in a magazine 73 for radio amateurs of...