Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 135

Circuit 112: Glass breakage detector
Setup information
Install the three transistors, the diode and the six resistors as shown in Fig. 2.112 The twelve jumper wires
come next. Last but not least connect the Piezo element. Check the placement on the board again and only
then connect.
Experiment
If everything is wired correctly, the small signals of the Piezo element, which in our case represents a micro-
phone, will be strongly amplified. At a certain threshold the red LED indicator turns on. The circuit is very
responsive to the noise of breaking glass. You can significantly increase the sensitivity of the Piezo element,
which is used as a microphone by using a sound plate or even a sound box. Read more about it in Chap.
1.2.3. That way you are able to monitor the breakage of glass panes, plus register other acoustic events
(thunder, loud air traffic and car noises, dog barking, etc.).
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.112.
Components required:
2 x 2N3904 transistors, 1 x 2N3906 transistor, 1 x red LED,
1 x 1 kΩ resistor, 2 x 10 kΩ resistors, 1 x 47 kΩ resistor,
2 x 470 kΩ resistors, 1 x 1 μF electrolytic capacitor, 2 x 10 μF
electrolytic capacitors, 1 x Piezo element, 1 x breadboard,
1 x 9V battery with clip connector
Fig. 2.112: Glass breakage detector
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