This circuit was found in 80's telecom documentation. Its purpose is to control a microphone in the process of transmitting voice and Morse signals.
If the battery is good, the LED flashes. This simple tester uses an LM3909 integrated circuit. We found...
This circuit was found in a 1926 German publication. It is a crystal or galena (D) receiver. The...
In the figure we have a typical configuration with operational, which can be different from the...