This simple indicator circuit was found in a documentation from the 90s. Trimpots can have values between 2k and 10k, a series resistor is recommended to limit the current to the minimum setting.
This circuit appears in several versions in publications of the time and can be modified by...
This configuration with FET and Unijunction can be found elsewhere on this site. The JFET admits...
We found this circuit in a Popular Electronics from the 90s. It operates at a frequency of 15 kHz....