Repel rodents with ultrasonic sound
The heart of our ultrasonic generator is a ATtiny25-20. To avoid the animals from becoming habituated, it generates a burst of roughly 1 second every 10 seconds. Since we humans cannot hear whether the circuit is active, an LED makes the operation of the circuit visible. The microcontroller itself is nowhere near capable of delivering enough current to drive a loudspeaker directly. So we added a BS170 MOSFET as a driver stage for the MPT-001 tweeter from Monacor.