Dog Repeller

In my earlier suburban ministry, I needed to contend with ... dogs. I was bitten (nipped) a few times, and once bloodied. I therefore built an ultrasonic dog repeller. It used a limited edition, powerful ultrasonic sounder. It would scare most dogs. But some dogs would be deaf, and a few would go wild. OBSERVATION: One can make such a device with off-the-shelf parts, and it may still be fairly effective. Here's one (pictured). One tunes a 4047B oscillator to a 25kHz ultrasonic sounder's resonant frequency. Replace R1 with a 2k2 multi-turn potentiometer, and tune the device for maximum current drain -- that's where you've hit the resonant frequency. B1 may be a miniature A23 battery (not that it will last long). Cats are even more sensitive to such devices.