Figure shows the connection diagram !
its a 311 opamp with 4 th terminal gnded
R2 is an LDR whose dark resistance is greater than 10kohm
A laser torch can be used to power the ckt which is directed at the
LDR !
when the light is falling on the LDR its resistance will be less than
10k ohm,then the voltage drop across the resistance will be less !
hence the o/p voltage of the opamp will be 0.When the light is
interrupted the resistance of the LDR increases hence droping more
voltage ,and the o/p will be approximately supply voltage .The o/p
can be connected across a buzzer and can be connected to a relay
if the alarm ,we want is of non stoping .ie ,it can be turned of only
by another process not by turning the light again.
the pin out of the 311
However the sytem provides no other extra security!
becoz if someone shows a light on the ldr and intrudes the laser then the
system may not be able to realise wat happened !So we must use some
extra security tecniques !
Those includes 1)frequency coding
2) Amplitude coding
etc
The fact here is that we can use any electronic component to implement a comparator
but a basic ckt may not be able to realise the practical situations in some cases we
may be using opamp active differetiators using R and c instead of RC passive differentiators.In such cases the opamp provides impedance matching along with amplification of the signal.So we must be able to realise which component of our design should dominate while its working and design accordingly!
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