This circuit was found in a 90s Popular Electronics. It is used for the acoustic transmitters of 40 kHz, as several found in this section. Transistors support current equivalents.
This instrumentation circuit was found in the September 1989 issue of Radio Electronics magazine....
This circuit was found in the November 1992 issue of Radio Electronics magazine. The circuit has...
This circuit was found in a British documentation from 1969. It can be implemented with modern...