This circuit was found in a 90s Popular Electronics. It also serves for the analysis of microcontroller signals. The power comes from the circuit under test.
This circuit was found in Japanese documentation from the 1960s. It is a commercial circuit with...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...
This simple receiver for listening on the phone was obtained in a 1960 documentation. The circuit is...