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Required parts: 9V battery*, 1K resistor (brown black red gold), 100K resistor (brown
black yellow gold), red LED, BC547 transistor, buzzer, 0,5m supplied wire.
How it works: An alarm sounds when the
normally closed security circuit (here
indicated as 'WIRE') is interrupted.
Replace
this
normally
(WIRE) by a normally closed window or
door switch; when e.g. the window is
opened the contact within the window
switch is interrupted, the security circuit is
opened and the buzzer sounds.
The alarm signal ends as soon as the
security circuit is closed again.
www.vellemanprojects.com
closed
circuit
Pag. 17
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