- on Audio/Video/Photography
- Published in issue 9/2008 on page 72
Ultrasonic Sound Detector
track down high frequencies
Using the circuit described here you can quickly and simply check whether harmful sounds with a high frequency are being produced somewhere nearby, especially important at locations where the so-called ultrasonic teen-deterrents against loitering youths are installed. Ten LEDs indicate the sound pressure of signals with frequencies between 16 and 40 kHz.