20-04-2012, 05:01 PM
SOUND OPERATED INTRUDER ALARM
SOUND OPERATED INTRUDER ALARM.pdf (Size: 108.06 KB / Downloads: 145)
Circuit Description
Initially , the opamp output and also the
(Q) output of hte flip flop are low . 555
timer (IC3) that is wired as an astable
multivibrator is reset due to the reset
terminal (pin - 4) being held low .
Transistor (Q 1) is in cut - off and the
relay coil stays de - energised . Both the
normally open contacts of the relay are
thus open. One of these contacts
(marked relay contact -1) Keeps them
lamp extinguished whereas the other
(marked relay contact -2 ) disconnects
the output of another timer IC (IC4) also
wired as ass astable multivibrator from
reaching the speaker.
Construction Guidelines
The PCB layout the components layout
are shown in and 3 respectively.
Testing Guidelines
The sensitivity adjust control should be
carefully set . Repeated testing should
be done to ensure that there are no false
triggers and that the gadget responds
when intended with almost 100 percent
reliability .