Emergency light using LM358 & LDR sensor

If you can imagine when you are crossing through any tunnel or any dark room you need to turn on the torch for clear view, now adding an additional advantage with automatic turning on at dark places will make is easier.

Emergency light using LM358

In our project we are making a shadow detector circuit which will sense the darkness. This sensor is just opposite to the light detector circuit. Here we are chasing darkness for indication.

As we have already made an IR Sensor and Light sensor circuit, In this project also we are going to use comparator circuit using LM358 IC.We are going to use one side as we need single side sensing task. In each port of this IC three pins are available which are non - inverting terminal PIN 2, inverting terminal PIN 3 and an output PIN 1. When voltage at non- inverting terminal is higher than inverting terminal the output gets high which means it will provide a voltage output as signal.

Pin Diagram-

Circuit diagram:

Component required:

LM358
Resistors R1 =1k

R2 = 10k

R3 = 330 Ohm

Variable resistor VR1 = 10k
LED
Transistor T1 BC547
LDR sensor
9v battery

Working:

In above circuit we have connected pin 2 LDR (Light dependent resistor) which is inverting terminal when light hits LDR sensor the ressistivity through it pins will be lowered and voltage supply will get high on the PIN 2 which results as low output at PIN1 . In our requirement we want to make a variable sensing device so that we can manipulate the sensitivity or set the value of darkness to be sensed . We add a variable resistor at PIN 3. As the variable resistor is set for low resistance, the voltage on PIN 3 gets high. The inverting terminal PIN 2 requires lower input signal to stay below the voltage on PIN 3 for higher output which means it is set for low intensity of light. As the resistance is improved the the sensitivity of the sensor increases due to lesser voltage requirement in PIN3.