AN2186 describes a low-cost, three-band acoustic glass break detector. Digital signal processing provides high sensitivity and sufficient resistance to false alarms.
Introduction
There are a variety of ways to implement glass break recognition. One method is to detect the vibration made by breaking glass. This technology may be realized using a piezo-film sensor for impact detection. Another method is to detect the sound of breaking glass. The simplest of such detectors are responsive to sound level spikes in the 4-5 kHz frequency band. The main disadvantage of the acoustic method is the high probability of false alarms caused by loud music, tinkling of bells, or other sounds. To increase false alarm immunity, two or more frequency bands are treated and information relating to amplitude and timing of the separated channels is analyzed.
