Glass Breakage Detector - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.49 Glass breakage detector

Circuit 111: Glass breakage detector
Setup information
Install the three transistors, the diode and the six resistors as shown in Fig. 2.111 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 the battery.
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. If the circuit is used for real, the Piezo element should be glued
to the glass pane that you wish to monitor. You could also use a relays instead of the red LED, which would
then trigger an alarm.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.111.
136
Components required:
2 x 2N3904 transistors,
1 x 2N3906 transistor,
1 x red LED, 1 x 1 kΩ resis-
tor, 2 x 10 kΩ resistors,
1 x 47 kΩ resistor,
2 x 470 kΩ resistors,
1 x 1 μF electrolytic capaci-
tor, 2 x 10 μF electrolytic
capacitors, 1 x Piezo ele-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.111: Glass breakage
detector