Velleman EDU01 User Manual download pdf (Page 15)

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Required parts: 9V battery*, 2x 1K resistor (brown black red gold), 2x 100K resistor

(brown black yellow gold), 2x red LED, 2 x BC547 transistors, 2x 10µF electrolytic

capacitors

The LED on-time can be calculated:

T = 0,693 x R1(Ω) x C1 (F)

T = 0,693 x 100.000 x 0.00001 = 0,693sec.

How it works: The 2 transistors

alternately conduct because the

capacitors are charged and discharged.

The speed at which this happens

depends on the capacitors (C1, C2)

and the resistors (R1, R2). Use a

higher capacitor and resistor value in

order to extend the LED lighting time.

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Velleman EDU01 User Manual Page 15