Some teenagers tend to congregate noisily near our house after midnight, flicking cigarette butts in our yard, clinking beer bottles, and disturbing our sleep. I was thinking of trying to repel them with high-frequency sounds, as some stores have done. I found a cheap, robust piezo horn tweeter (53-805) in the MCM catalogue. I could just record some 18 - 20 kHz test tones on a CD, but I wondered if there's a simple oscillator circuit that I could build to feed an old receiver to drive the tweeter, thus just flipping a switch instead of playing a CD when needed.
Jan