Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 120

Circuit 97: A needle fidgets in waltz time
Setup information
Install the two transistors, the LED, the four resistors and the three electrolytic capacitors as shown in
Fig. 2.97 Then connect the moving-coil instrument. Finally, insert the 13 jumper wires. Check the placement
on the board again and only then connect the battery.
Experiment
If everything is wired correctly, the slow beat starts with a short delay. The red LED will go on in intervals
and the needle of the moving-coil instrument will swing full-scale.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.97.
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Components required:
2 x 2N3904 transistors,
1 x red LED, 2 x 220 kΩ
resistors, 1 x 4.7 kΩ resis-
tor, 1 x 1 kΩ resistor,
1 x 100 μF electrolytic
capacitor, 2 x 10 μF
electrolytic capacitors,
1 x moving-coil instrument,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.97: A needle fidgets in
waltz time