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2.48 Hawaiian guitar
Circuit 110: Hawaiian guitar
Setup information
Install the two transistors, the two resistors, the ceramic capacitor and the electrolytic capacitor as shown in
Fig. 2.110 The seven jumper wires come next. Last but not least connect the Piezo element and the external
resistor R1. 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 everything is wired correctly, you will hear a melodic sound once the battery is connected. The pitch is
defined by the external R1 resistor. If the value is 0 Ω, the audio frequency is at approximately 5 kHz, at 500
kΩ the frequency drops to about 100 Hz. In our case, you can realize the resistor in form of a small finger-
board. Take a sheet of a thick drawing cardboard (about 15 x 5 cm). With a soft pencil draw a fat line about
1 cm wide all the way from top to bottom. One end of the line is connected to the circuit. Take a second
wire and drive along this line. This will produce the typical sound of a Hawaiian guitar. You could also build
yourself a small resistance register, which you could play just like a keyboard.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.110.
Components required:
1 x 2N3904 transistor,
1 x 2N3906 transistor,
1 x 1 kΩ resistor, 2 x 22 kΩ
resistors, 1 x external resis-
tor (see Experiment for
value), 1 x 10 nF ceramic
capacitor, 1 x 10 μF elec-
trolytic capacitor, 1 x Piezo
element, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.110: Hawaiian guitar
135
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