This circuit is from a 1980's documentation for telecommunications. The circuit is used in SSB and the diodes must be suitable types for the application. The audio input is low impedance.
July 2016 - It can be obtained from Mouser Electronics new trinkets Adafruit. These trinkets are...
This circuit allows you to read resistors up to 20 M ohms, converting it into voltage. The circuit is...
In fact, this is the circuit also known as “vox”, that is, a relay triggered by sound. This...