Found in a 90s Popular Electronics, this circuit excites a 40 kHz ultrasonic transducer. The transistor can be a BD135 or other medium power.
This circuit is intended for communications receivers. We can find it in a documentation from the...
We found this circuit in a994 documentation. It has a visual and a time signature indicator in...
This circuit for very low frequencies was found in an American documentation from the 90's....