112
2.36 Metronome
Circuit 87:
Metronome with discreet unijunction transistor
Setup information
Install the two transistors, the four resistors and the two electrolytic capacitors as shown in
Fig. 2.87.
The
nine 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. You can significantly increase the sensitivity of the Piezo ele-
ment by using a sound plate or even a sound box. Read more about it in Chap. 1.2.3
Components required:
1 x 2N3904 transistor,
1 x 2N3906 transistor,
1 x 1 k
Ω
resistor,
2 x 2.2 k
Ω
resistors,
1 x 220 k
Ω
resistor,
1 x resistor, see box Experi-
ment, 1 x 1 μF electrolytic
capacitor, 1 x 10 μF elec-
trolytic capacitor, 1 x Piezo
element, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.87:
Metronome with
discreet unijunction transistor
Experiment
If everything is wired correctly, you will not hear anything once the battery is connected. Up to now you still
don’t know the value of resistor R2. This resistance defines the metronome pulse. Details are listed below:
Resistor R2
pulse
47 k
Ω
50 bpm
22 k
Ω
80 bpm
10 k
Ω
180 bpm
If you use a potentiometer (value 50 k
Ω
or 100 k
Ω
) instead of a fixed resistor, you can adjust the pulse
continuously. On a side note: The two transistors are wired in a way that they will function like a unijunc-
tion transistor.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.87.
Summary of Contents for ELECTRONICS EXPERIMENTS BOX
Page 4: ......
Page 265: ...267 Fig 3 56 Cir cuit 56 Audio limiter Fig 3 57 Circuit 57 Amplifier for a storm detector...
Page 269: ...271 Fig 3 64 Circuit 64 Stabilizer for 1 9 V Fig 3 65 Circuit 65 Stabilizer for 2 5 V...
Page 275: ...277 Fig 3 80 Circuit 80 Quiztimer 30 seconds Fig 3 81 Circuit 81 Handy diode tester...
Page 315: ...317 Fig 3 179 Circuit 179 HF generator 150 kHz Fig 3 180 Circuit 180 HF generator 420 kHz...
