Bicycle Light - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.11 Bicycle light

Circuit 29: Simple bicycle light
Setup information
Install the transistor and the two diodes as shown in Fig. 2.29. Then install the three resistors and the
electrolytic capacitor. The seven jumper wires come next. The the jumper acting as switch (shown dashed)
is installed last. Only one end of the jumper wire is connected, the other is open. 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. When the
switch is closed, the LED light turns on. But when you open the switch, the LED will not turn off immediately
but will continue to glow for a while. At this point it is important that the light emitting diode is switched
via the transistor and the actual switch only needs to master the tiny control current of this transistor.
This will eliminate corrosion on the switching parts caused by switch sparks. 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. 3.29.
54
Components required:
1 x 2N3904 transistor,
1 x yellow LED,
1 x 1N4148 silicon diode,
1 x 470 Ω resistor,
1 x 1 kΩ resistor,
1 x 10 kΩ resistor,
1 x 100 μF elec-
trolytic capacitor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.29: Simple bicycle light