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Circuit 37: Diode tester
Setup information
Install the two transistors, the diode and the four resistors as shown in Fig. 2.37. Install the two ceramic
capacitors and the electrolytic capacitor followed by nine jumper wires. Finally connect the Piezo element.
Check the placement on the board again and only then connect the battery.
You can significantly increase the sensitivity of the Piezo element by using a sound plate or even a sound
box. Read more about it in Chap. 1.2.3
Experiment
If the diode to be tested is forward biased, you can hear a high-pitched sound, if reversed biased you won't
hear anything or a very deep tone. This indicates that the diode is in order.
This circuit works with all kinds of diodes: Germanium, silicon, Schottky and LED. If you hear a sharp tone
twice, nothing at all or only a deep tone, then the diode is faulty. The acoustic signalising qualifies this
circuit for conducting mass diode tests according to the pattern "go – no go".
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.37.
62
Components required:
2 x 2N3904 transis-
tors, 1 x 1N4148
silicon diode, 2 x 1 kΩ
resistors, 2 x 10 kΩ
resistors, 2 x 100 nF
ceramic capacitors,
1 x 10 μF electrolytic
capacitor, 1 x Piezo ele-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.37: Diode tester
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