Gate Alarm Circuit Diagram

Figure 1 represents a cheap and simple Gate Alarm Circuit, that is intended to run off a small universal AC-DC power supply.

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IC1a is a fast oscillator, and IC1b is a slow oscillator, which is combined through IC1c to emit a high pip-pip-pip warning sound when a gate (or window, etc.) is opened. The circuit is intended not so much to sound like a siren or warning device, but rather to give the impression: “You have been noticed.” R1 and D1 may be omitted, and the value of R2 perhaps reduced, to make the Gate Alarm sound more like a warning device. VR1 adjusts the frequency of the sound emitted.

IC1d is a timer that causes the Gate Alarm to emit some 20 to 30 further pips after the gate has been closed again before it falls silent as if to say: “I`m more clever than a simple on-off device.” Piezo disk S1 may be replaced with a LED if desired, the LED being wired in series with a 1K resistor.

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