Wednesday, 23 January 2013
Saturday, 12 January 2013
Dark detector is a circuit which can detect the presence of light in the sensor proximity. Here we would be using 555 as the heart of the circuit and l.d.r as sensor.
· When the light is incident on l.d.r the resistance offered by it decreases this property is used for detecting light
Resistance =directly proportional to light intensity
· Here 555 is used as a monostable multivibrator which changes its output depending on the trigger input whenever the trigger is below 1/3vcc lower comparator sets and it sets output to high
· Here l.d.r and rgnd forms a potential divider creating drop in voltage whenever light intensity falls beyond a certain limit i.e <1/3*vcc. Causing high resistance across l.d.r .there by creating a low potential at trigger pin thus causing output to
· The period of ton depends on the equation as :
· From output(3rd pin) we are connecting a relay so that we can control an a.c load and l.e.d is used here to provide an indication that relay is switched on.
· The relay would be switched on until the light intensity is maintained below the cutoff point i.e voltage at trigger pin is below 1/3vcc.
· A diode is provided to prevent “kickback” of inductor in relay
· Sensitivity of the circuit depends on the area of l.d.r for high sensitivity we can go for >6m.m ldr.
(cicuit provided by electro club,DVRCET)