We found this circuit in the July 1988 Radio Electronics magazine. The frequencies are given by capacitor C1 and the voltage input is made at pin 1.
This simple circuit does not use active components and uses a small speaker as a microphone. The...
Any power MOSFET that supports the current of the controlled stepper motor can be used on this...
This circuit is from the 1990 Motorola Linear Databook. The circuit can be implemented with other...