HOW TO MAKE LDR SENSOR AT HOME

HOW TO MAKE LDR SENSOR AT HOME

HOW TO MAKE LDR SENSOR AT HOME

Prepared by

Name: - Kumawat ajay kumar

College: - S&S.S. Gandhi Polytechnic college, Surat

Introduction

A photo resistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photo resistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity.

A photo resistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.

A photo resistor is made of a high resistance semiconductor. In the dark, a photo resistor can have a resistance as high as a few mega ohms (MΩ), while in the light, a photo resistor can have a resistance as low as a few hundred ohms. If incident light on a photo resistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons and hole conduct electricity, thereby lowering resistance.

The resistance range and sensitivity of a photo resistor can substantially differ among dissimilar devices. Moreover, unique photo resistors may react substantially differently to photons within certain wavelength bands.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon.

In intrinsic devices, the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire band gap.

Extrinsic devices have impurities, also called do pants, and added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor.


To Make LDR Sensor at home, first, we need some components as listed below.

1) LDR ×1
2) Resistor ×2 (47kΩ, 470Ω)
3) Sl100 transistor ×2
4) LED
5) Breadboard (PCB plate)
6) Jumper wire
7) Red and black wire
8) 5v supply



1) LDR


An LDR is a component that has a resistance that changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits.

2)Resistor



The resistor is an electrical component that reduces the electric current. The resistor's ability to reduce the current is called resistance and is measured in units of ohms (symbol: Ω).

3)SL100 Transistor


SL100 is a general purpose, medium power NPN transistor. It is mostly used as a switch in common emitter configuration.
The transistor terminals require a fixed DC voltage to operate in the desired region of its characteristic curves. 
This is known as the biasing. For switching applications, SL100 is biased in such a way that it remains fully on if there is a signal at its base.

4) LED

LEDs, or light-emitting diodes, are semiconductor devices that produce visible light when an electrical current passed through them. 

LEDs are a type of Solid State Lighting (SSL), as are organic light–emitting diodes (OLEDs) and light–emitting polymers (LEPs).

5) Breadboard (PCB plate)                  

A breadboard is a construction base for prototyping of electronics. This makes it easy to use for creating temporary prototypes and experimenting with circuit design. For this reason, solder fewer breadboards are also extremely popular with students and in technological education.

6) Jumper wire 




A jump wire is a short electrical wire with a solid tip at each end which is normally used to interconnect the components in a breadboardThe "end connectors" are inserted into the breadboard, without welding, in the particular slots that need to be connected in the specific prototype.

7)   Red and black wire

In DC circuits, the positive pole is usually marked red (or "+") and the negative pole is usually marked black (or "−"), but other color schemes are sometimes used in automotive and telecommunications systems.



8) Power supply

In Power Supply you can use the 9V battery in this circuit.



Schematic Diagram of LDR Sensor



Cost list of LDR Sensor circuit
         
Sr. No.
Name
Quantity
Rate(Rs.)
1
Led
1
2
2
LDR
1
10
3
Transistor( SL100)
2
30
4
Resistor (47kilo ohm)
2
2
5
Battery (9V)
1
20
6
PCB board
1
20
Total
84