Velleman EDU01 User Manual download pdf (Page 29)

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Pag. 29

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 Darlington switch hence only a very small current is needed

to make T1 conduct and activate the alarm sound.

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Velleman EDU01 User Manual Page 29