Light Sensitive Switch - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.22 Light sensitive switch

Circuit 53: Light sensitive switch with green LED
Setup information
Install the two transistors, the two diodes and the two resistors as shown in Fig. 2.53. The three jumper
wires come next. Check the placement on the board again and only then connect the battery.
Experiment
This circuit tells you whether the sensor surroundings are bright or dark. The green LED functions as sensor.
Its reverse current increases noticeably when light shines on the sensor. This will turn on the red LED. It can
be utilised in many ways: Light barriers, remote release for animal photos, room surveillance and the like.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.53.
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Components required:
2 x 2N3904 transistors,
1 x green LED, 1 x red LED,
1 x 1 kΩ resistor,
1 x 100 kΩ resistor,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.53: Light sensitive switch
with green LED