Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 63

Circuit 40: High pass from on 5.5 kHz
Setup information
Install the transistor and the three resistors as shown in Fig. 2.40. Then install the two ceramic capacitors
and the electrolytic capacitor. The five jumper wires come next. Finally connect the Piezo element. Check
the placement on the board again and only then connect the battery.
You can increase the sensitivity of the Piezo element significantly by using a sound plate or even a sound
box. Read more about it in Chap. 1.2.3
Experiment
A high pass filter lets high-pitched tones pass through and blocks deep tones. In our circuit, only signals
with a frequency above 5.500 Hz can pass through. Connect the output of an mp3 player to the input.
You often can't hear the music played – very high-pitched sounds are rare. Voice recordings can't be distin-
guished at all. The limit of the cut-off frequency is determined by the values of C1, C2 and R2.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.40.
Components required:
1 x 2N3904 transistor,
1 x 2.2 kΩ resistor,
1 x 22 kΩ resistor,
1 x 100 kΩ resistor,
2 x 10 nF ceramic capaci-
tors, 1 x 10 μF electrolytic
capacitor, 1 x Piezo ele-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.40: High pass 5.5 kHz
onwards
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