Velleman EDU01 User Manual download pdf (Page 19)

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Pag. 19

Required parts: 9V battery*, 1K resistor (brown black red gold), 2x 10K resistor

(brown black orange gold), red LED, BC547 transistor, LDR.

How it works: A LED lights up when enough

light hits the LDR. The LDR is a light sensitive

resistor (Light Dependent Resistor), in dark

conditions it has a high resistance, and in light

conditions its resistance becomes low.

Across the LDR is a positive potential which is

fed to the base of the transistor enabling it to

switch. Resistor R2 creates a switching point

which determines when the transistor starts to

conduct. Resistor R1 limits the current that

flows through the LDR.

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Velleman EDU01 User Manual Page 19