This ultrasonic dog repeller circuit will chase away angry dogs. It is build with the all known 555 circuit, a buzzer and a little ferrite transformator. The ultrasonic frequency must be set with a dog nearby.
Circuit number 1 uses the well known NE555 IC, couple of components and a EE15 ferrite transformer. Adjust R3 at resonance frequency of the piezo transducer for maximum aplitude of the repeller ultrasonic sound. At 30 KHz this can reach a value of 108 Vpp. Without the piezo the output voltage is around 200 Vpp.
breadboard and oscilloscope screen captures
I have replaced the 10nF capacitor with a 6.8nF one so it can cover a frequency range between 11kHz and 25kHz, but in your case it might work with the 10nF. The output voltage has a value of 10Vpp and the buzzer is a passive one (without generator).