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Required parts: 9V battery, 10K resistor (brown black orange gold), 470K resistor
(yellow purple yellow gold), buzzer, 2x BC547 transistor, 2 wires
How it works: The 2 sensor wires
must be placed in a tank at a certain
distance (e.g. use a drinking cup). Fill
up the tank with a conducting liquid
(e.g. water) until the level reaches
both sensor wires. A small current
will flow via R2 towards the base of
T2. The base is protected against
interference with a resistor R1.
T1 & T2 are configured as a Darling-
ton switch hence only a very small current is needed to make T1 conduct and activate
the alarm sound.
www.vellemanprojects.com
Pag. 29
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