Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 53

Circuit 30: Automatic bicycle light with solar cell
Setup information
Install the transistor and the two diodes as shown in Fig. 2.30. Then install the three resistors and the
electrolytic capacitor. The six jumper wires come next. The solar cell is installed last. Check the placement
on the board again and only then connect the battery.
Experiment
Even if everything is wired correctly, nothing will happen at first; the yellow LED remains dark. As long as
light falls on the solar cell, it will keep the LED turned off by means of the transistors. But once it is dark,
the transistor T2 will switch on the LEDs. C1 ensures that switch-off is delayed so that a momentary shadow
or light incidence won't lead to switching operations that are not intended. If you are indeed using the cir-
cuit as bicycle light, you should use a super bright white LED and there ought to be a hub dynamo installed.
Traffic regulations must be observed.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.30.
Components required:
1 x 2N3904 transistor,
1 x yellow LED, 1 x 1N4148
silicon diode, 1 x solar
cell, 1 x 470 Ω resistor,
1 x 22 kΩ resistor,
1 x 47 kΩ resistor,
1 x 100 μF electrolytic
capacitor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.30: Automatic bicycle
light with solar cell
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