This circuit has an automatic dynamic gain control in a range of 6 dB to 40 dB. We found it in documentation from the 90s. The bipolar transistor is a general purpose type.
This circuit, found in an American publication from the 1970s, produces an audible tone in a...
This circuit was found in a 2006 publication. It can serve as the basis for a microcontrolled...
By adding a transistor to the output and some polarization features we can obtain a higher output...