Relay

Q.Why do we use relay in a circuit?how far it is different from other switches?Is there any component which can act as substitute to relay?

Inside USB

1 USB Standard, Male A-plug
2 USB mass storage controller device
3 Test points
4 Flash memory chip
5 Crystal oscillator
6 LED (Optional)
7 Write-protect switch (Optional)
8 Space for second flash memory chip

Inside a 3pin plug

Semi Conductor Outlines

Evolution of Processor

Cell phone internal structure

Dark Detector

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.

Components:

Resistors-3,Capacitor-1,l.d.r-1,555-1,12v supply-1,l.e.d(5mm)-1,relay(9v)-1

Working:

·         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 :

Ton=1.1*r2*c1

·         From output(3^rd 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)