Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 45

Circuit 22: Flashing bicycle light
Setup information
Install the two transistors as shown in Fig. 2.22. Install the two white LEDs. If you do not have white LEDs,
use a green and a yellow instead. Now it is time for the four resistors and the two electrolytic capacitors.
Finally, insert the six jumper wires.
The circuit could be used as flashy bike tail light if the assembly is somehow water-resistant. Check the
placement on the board again and only then connect the battery.
Experiment
If everything is wired correctly, the two LEDs will start flashing alternately. This may attract more attention
than just a static light. It should be powered by a DC hub dynamo when used on a bike. Traffic regulations
must be observed.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.22.
Components required:
2 x 2N3904 transistors,
2 x white LEDs (not
included), 2 x 100 Ω resis-
tors, 2 x 22 kΩ resistors,
2 x 10 μF electrolytic
capacitors, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.22: Flashing bicycle light
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