Flashing Bicycle Light - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.8 Flashing bicycle light

Circuit 21: Flashing tail light
Setup information
Install the two transistors as shown in Fig. 2.21. Install the two red LEDs. Now it is time for the four resistors
and the two electrolytic capacitors. Finally Insert the six jumpers.
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. This is a fundamental building block used in modern digital electronics, the multi-
vibrator. Basically, every electronic device (calculator, mobile phone, PC, etc.) contains this basic circuit. 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. 3.21.
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Components required:
2 x 2N3904 transistors,
2 x red LEDs, 2 x 1 kΩ
resistors, 2 x 22 kΩ resis-
tors, 2 x 10 μF electrolytic
capacitors, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.21: Flashing tail light