www.vellemanprojects.com
Pag. 15
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 high-
er capacitor and resistor value in order
to extend the LED lighting time.
