56
Circuit 31:
Automatic bicycle light with phototransistor
Setup information
Install the two transistors as shown in
Fig. 2.31.
Then the two resistors and the electrolytic capacitor are
installed. The five jumper wires come next. Check the placement on the board again and only then connect
the battery.
Components required:
1 x 2N3904 transistor,
1 x PT331C phototransistor,
1 x yellow LED, 1 x 470
Ω
resistor, 1 x 47 k
Ω
resis-
tor, 1 x 100 μF electrolytic
capacitor, 1 x breadboard,
1 x battery, 9V battery with
clip connector
Fig. 2.31:
Automatic bicycle light
with phototransistor
Experiment
Even if everything is wired correctly, nothing will happen at first; the yellow LED remains dark. As long as
light falls on the phototransistor, it will keep the LED turned off by means of T2. 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 circuit 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. 3.31.
Summary of Contents for ELECTRONICS EXPERIMENTS BOX
Page 4: ......
Page 265: ...267 Fig 3 56 Cir cuit 56 Audio limiter Fig 3 57 Circuit 57 Amplifier for a storm detector...
Page 269: ...271 Fig 3 64 Circuit 64 Stabilizer for 1 9 V Fig 3 65 Circuit 65 Stabilizer for 2 5 V...
Page 275: ...277 Fig 3 80 Circuit 80 Quiztimer 30 seconds Fig 3 81 Circuit 81 Handy diode tester...
Page 315: ...317 Fig 3 179 Circuit 179 HF generator 150 kHz Fig 3 180 Circuit 180 HF generator 420 kHz...
