| 摘要 |
An improved acoustic burglar alarm detects an aperiodic wave resulting from opening of a door or window, and adapts the threshold level, which discriminates between alarm events and non-alarm events, according to the ambient environment, thereby preventing wind from setting off an alarm, yet maintaining adequate sensitivity. The detection system features a microphone 1, preferably of electret type, a threshold comparator 5, a filtering circuit 7, a window comparator acting as a peak value detector, an integrator circuit 9, a voltage monitor 10, and an oscillator-counter 14. A monostable 16 triggers a relay 21 which sets off the alarm. A switch 15 permits selection between two alternate operating modes.
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