A
PROJECT REPORT
ON
“LIGHT SENSOR”
Submitted in partial fulfilment of Bachelor’s Degree in Technology, Rajasthan Technical University,
Kota.
[Session: 2010-2011]
Submitted to:
Submitted by:
Ms. Garima Mathur Naresh Kumar Mishra(EC08071)Head Nekendra Sharma(EC08072) Deptt. Of ECE Nikhil Bali(EC08073)
Nikhil Kumar(EC08074)
Department of Electronics & Communication Engineering
Jaipur Engineering College,
JAIPUR ENGINEERING COLLEGE, KUKAS
JAIPUR
[Session 2010-2011]
CERTIFICATE
This is to certify that Minor Project report entitled “LIGHT \DARK SENSOR”, submitted by Naresh Kumar Mishra, Nekendra Sharma, Nikhil Bali, Nikhil
Kumar, students of Third year B.Tech in Electronics & Communication, JAIPUR
ENGINEERING COLLEGE, KUKAS, JAIPUR was completed under my supervision and their work was found satisfactory and I found them sincere towards the work.
Mrs. Garima Mathur Mr. Prashant Pareek
ACKNOWLEDGEMENT
A scholarly and quality work like designing of any project
can be accomplished by motivation, guidance and inspiration of certain
quarters besides the individual efforts. We express our heartiest gratitude
to those who have helped us in various stages of this study.
We are very much thankful to Ms. Garima mathur, Head of department,
ECE, for providing all necessary facilities. We extend our sincere thanks
to our project guide Mr. Prashant pareek, Lecturer, ECE, for giving us
permission to undergo this project and for his valuable guidance and
co-operation.
Naresh kumar Mishra(EC08071) Nekendra Sharma(EC08072) Nikhil Bali(EC08073) Nikhil Kumar(EC08074)
PREFACE
Engineering is not only a theoretical study but it is a implementation of all we study for creating something new and making things more easy and useful through practical study.
It is an art which can be gained with systemic study, observation and practice. In the college curriculum we usually get the theoretical knowledge of industries and a little bit of implantation knowledge that how it work’s? But how can we prove our practical knowledge to increase the productivity or efficiency of the industry?
To overcome such problem we the students of JAIPUR ENGINEERING COLLEGE, KUKAS, JAIPUR are supposed to make a project on “LIGHT SENSOR”
A light sensing circuit is extremely useful and versatile in a wide range of renewable energy projects from automatic lighting to security systems. In this project we have tried to explain the variation of current with variation of light. For this purpose we have used Light Dependent Resistor (LDR). The basic use of this interrelation is in street lights and in control alarms. Using this principle automatic switching of lamps is done.
INDEX
S.No.
TITLE
PAGE NO.
1. Introduction...1 2. Circuit Diagram...2 3. Circuit Discription...3 4. Working ...4 5. Component table...5 5.1 Data Sheet of 741 IC 5.2 Light dependent resister(LDR) 5.3 Relays 5.4 Transistor 6. Printed Circuit Board...15
6.1 Types Of PCB 6.2 Manufacturing Process Of PCB 7. PCB layout...19 8. Applications...20 Conclusion References
1.
INTRODUCTION
Light sensor circuit is widely used in projects for security systems and light control. In our project we have performed sensing operation using a light dependent resistor (LDR). This circuit will activate a relay when light falls to a preset level. This kind of circuit is basically used in automatic turn on and off of street light, security alarm etc. For this project various components like transistor, relay, potentiometer, resistor, capacitor, diode and 741 IC are used. Components and there datasheets and working is being described in the report.
2.CIRCUIT DIAGRAM
3.CIRCUIT DESCRIPTION
The light sensor used is the ORP12 photocell. According to this circuit, a relay will be activated when light falls to a preset level. Light level can be adjusted with
potentiometer and the relay contacts may be used to operate an external light or buzzer.
Transistor is being used here as a switch. A diode is also connected which is used for the protection of relay. LM 741 works as a comparator IC. LED is being used for indication switching circuit.
By swapping the positions of the 10K resistor (R1) and the LDR (LDR1), the relay will be closed when the LDR is under light rather than under darkness. Therefore a device can automatically be switched off at night time.
Since this circuit still contains a relay we need to make some changes to reduce the amount of power to make it more suitable for renewable resource powered low-current applications.
4. WORKING
In our project “LIGHT SENSOR” the main sensing component used is LDR (light dependent resistor). It follows the principle that intensity of light falling is inversely proportional to resistance i.e. negative temperature coefficient. The light sensor used is the ORP12 photocell. In bright light the resistance of the ORP12 can be as low as 80 ohm and at 50 lux(darkness) the resistance increases to over 1Mohm. The 1M control should provide a wide range for light intensities, if not its value may be increased.
The op-amp senses the voltage difference between pins 2 and 3. The control VR1 is adjusted so that the relay is off, the output of the op-amp will be around 2 volts. When light falls, the resistance of the photocell increases and the difference in input voltage is amplified by the op-amp, the output will swing towards full supply and drive the transistor and relay.
The 270k resister provides a small amount of hysteresis, so that the circuit switches on and off with slightly different light levels. This eliminates relay chatter.
Now when the LDR is covered, the potential at collector junction increases which drives the relay on, during this relay is normally open due to which LED glows. The glowing of LED indicates the sensing of light and dark conditions.
5.COMPONENT TABLE
S.No. COMPONENTS QUANTITY SPECIFICATIONS
1 LM741 1 Works as a comparator IC
2 POTENTIOMETER 1 10K helps in voltage biasing
3 DIODE 1 1N4001 is used for
protection of relay
4 TRANSISTOR 1 BC548 works as a switch
5 RESISTOR 2 2 1 470 Ω, 1 Watt 10 K, 2 Watt 1 K, 1 Watt 6 RELAY 1 6V, 50Hz
7 LDR 1 For light sensing
8 LED 1 For indication switching
circuit
9 POWER SUPPLY 1 Used to give supply to the
circuit
10 BREAD BOARD 1 Used for connections
Figure 6.1- Circuit of LM741
5.2 LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor is a component that is sensitive to light. When light falls upon it then the resistance changes. Values of the resistance of the LDR may change over many orders of magnitude the value of the resistance falling as the level of light increases.
It is not uncommon for the values of resistance of an LDR or photoresistor to be several megohms in darkness and then to fall to a few hundred ohms in bright light. With such a wide variation in resistance, LDRs are easy to use and there are many LDR circuits available.
LDRs are made from semiconductor materials to enable them to have their light sensitive properties. Many materials can be used, but one popular material for these photoresistors is cadmium sulphide (CdS).
Light dependent resistors or LDRs are often used in circuits where it is necessary to detect the presence or the level of light. They can be described by a variety of names from light dependent resistor, LDR, photoresistor, or even photo cell (photocell) or photoconductor.
Although other devices such as photodiodes or photo-transistor can also be used, LDRs are a particularly convenient electronics component to use. They provide large change in resistance for changes in light level.
In view of their low cost, ease of manufacture, and ease of use LDRs have been used in a variety of different applications. At one time LDRs were used in photographic light meters, and even now they are still used in a variety of applications where it is necessary to detect light levels.
The device is used in control circuits to turn lights on and in photographic exposure meters.
How an LDR works
An LDR or photoresistor is made of any semiconductor (such as Cadmium Sulphide) material with a high resistance. It has a high resistance because there are very few electrons that are free and able to move – the vast majority of the electrons are locked into the crystal lattice and unable to move. Therefore in this state there is a high LDR resistance.
As light falls on the semiconductor, the light photons are absorbed by the
semiconductor lattice and some of their energy is transferred to the electrons. This gives some of them sufficient energy to break free from the crystal lattice so that they can then conduct electricity. This results in a lowering of the resistance of the
semiconductor and hence the overall LDR resistance.
The resistance of the LDR decreases as the intensity of the light falling on it increases. Incident photons drive electrons from the valency band into the conduction band.
5.3 RELAYS
A relay is usually an electromechanical device that is actuated by an electrical current. The current flowing in one circuit causes the opening or closing of another circuit. Relays are like remote control switches and are used in many applications because of their relative simplicity, long life, and proven high reliability. They are used in a wide variety of applications throughout industry, such as in telephone exchanges, digital computers and automation systems.
How do relays work?
All relays contain a sensing unit, the electric coil, which is powered by AC or DC current. When the applied current or voltage exceeds a threshold value, the coil activates the armature, which operates either to close the open contacts or to open the closed contacts. When a power is supplied to the coil, it generates a magnetic force that actuates the switch mechanism. The magnetic force is, in effect, relaying the action from one circuit to another. The first circuit is called the control circuit; the second is called the load circuit. A relay is usually an electromechanical device that is actuated by an electrical current.
The current flowing in one circuit causes the opening or closing of another circuit.
Figure.5.3.1 Relay
10
Datasheet:-FEATURES
•Ultra-miniature size with universal terminal footprint •High contact capacity: 10 A
•Class B coil insulation type available •TV-5 type available
1 Form A type → TV-5
1 Form C type → TV-5 (N.O. side only) •VDE, TÜV also approved
•Sealed construction for automatic cleaning
SPECIFICATIONS Contact
Arrangement 1 Form A, 1 Form C Initial contact resistance,
max.
100 mΩ (By voltage drop 6 V DC 1
A)
Contact material Silver alloy 10 A 250 V AC Nominal switching capacity 10 A 125 V AC Rating 6 A 277 V AC (resistiv e Max. switching power 2,500 VA
load) Max. switching
voltage 250 V AC, 100 V DC Max. switching current 10 A (AC), 5 A (DC) Mechanical (at 180 cpm) 107 Expecte d Electrical at 10 A 125 V AC, 6 A 277 V AC resistive 105 Life (at 20 cpm) (min.op
Characteristics
Max. operating
speed 20 cpm
Initial insulation
resistance Min. 100 MΩ (at 500 V DC) Initial Between open contacts 750 Vrms for 1 min. Breakdown Between contacts and
coil 1,500 Vrms for 1 min. voltage*1 Operate time*2 Approx. 10 ms (at nominal voltage)
Release time(without diode)*2 (at
nominal
Approx. 10 ms voltage)
Temperature rise (at nominal
voltage) Max. 35°C Shock resistance Functional*3 Min. 98 m/s 2 {10 G} Destructive* 4 Min. 980 m/s 2 {100 G} Approx. 98 m/s2 {10 G}, Functional*5 10 to 55 Hz at double Vibration amplitude of 1.6 mm Resistanc e 2 Approx. 117.6 m/s {12 G}, Destructive 10 to 55 Hz at double amplitude of 2 mm Conditions for operation, Ambient –40°C to +85°C transport and storage*6 temp.*7 –40°F to +185°F
(Not freezing and condens-Humidity 5 to 85% R.H. ing at low temperature) Unit weight Approx.12 g .423 oz
Table 12.1- Characteristics of relay
ADVANTAGES OF RELAYS:
• Relays can switch AC and DC, transistors can only switch DC. • Relays can switch higher voltages than standard transistors.
• Relays are often a better choice for switching large currents (> 5A). • Relays can switch many contacts at once.
DISADVANTAGES OF RELAYS:
• Relays are bulkier than transistors for switching small currents.
• Relays cannot switch rapidly (except reed relays), transistors can switch many times per second.
• Relays use more power due to the current flowing through their coil.
• Relays require more current than many ICs can provide, so a low power transistor may be needed to switch the current for the relay's coil.
5.4 Transistor
QUICK REFERENCE DATA
Table 14.1- Characteristics of transistor
14 FEATURES
• High current (max. 800 mA)
• Low voltage (max. 40 V).
APPLICATIONS
• Linear amplification and switching.
DESCRIPTION
• NPN switching transistor in a TO-18 metal package.
6 . PRINTED CIRCUIT BOARDS
The use of miniaturization and sub miniaturization in electronic equipment design has been responsible for the introduction of a new technique in inters component wiring and assembly that is popularly known as printed circuit.
The printed circuit boards (PCBs) consist of an insulating substrate material with metallic circuitry photo chemically formed upon that substrate. Thus PCB provides sufficient mechanical support and necessary electrical connections for an electronic circuit.
Advantages of printed circuit boards:
-1) Circuit characteristics can be maintained without introducing variations inter circuit capacitance.
2) Wave soldering or vapour phase reflow soldering can mechanize component wiring and assembly.
3) Mass production can be achieved at lower cost.
4) The size of component assembly can be reduced with corresponding decrease in weight.
5) Inspection time is reduced as probability of error is eliminated.
6.1 TYPES OF PCB’S
There are four major types of PCB’s:
-1) Single sided PCB: - In this, copper tracks are on one side of the board, and are the simplest form of PCB. These are simplest to manufacture thus have low production cost.
2) Double sided PCB:- In this, copper tracks are provided on both sides of the substrate. To achieve the connections between the boards, hole plating is done, which increase the manufacturing complexity.
6.2 DESIGNING OF PCB
PCB can be manufactured by a number of processes. One of the processes is mentioned
below:STAGE 1: Lith film manufacture
Lith film (photo film) used in this process was earlier used for black and white photography. REMEMBER: All the processes for the manufacture of lith film are performed in the dark room under minimal amount of light.
Before beginning with the steps we prepare 3 trays of solutions:
Tray 1: A+B tray which is Butyl + Sodium Carbonate with concentration 1 teaspoon in 1 litre of water both added in same ratio.
Tray 2: Ordinary water
Tray 3: It consists of fixer (developer), the chemical is dissolved 2 teaspoons in 1 litre of water.
1. The first step is to prepare the layout of the circuit on a transparent sheet. 2. Lith film is a sheet with two sides, one side is brown and the other is gray. 3. The lith film is now cut to an approximate size of the layout.
4. The lith film is now placed in the lith making machine with readable part on the upper side.
5. The brown side of the lith film should touch the layout.
6. Now put the door of the machine down for not more than 8 seconds and push the switch ON.
7. Remove the lith film and wash it in the first tray continuously in movement till the complete circuit is developed. Minimum time required is 2-3 minutes.
8. The circuit after the first tray appears transparent and the rest of the film turns black. 9. Now shift the lith film in second tray and wash it for 2-3 minutes.
10. Lastly wash the lith film in the fixer tray for the same time interval.
11. Now, dry the film in air/oven at normal temperature say 40 degrees till the film dries.
The negative is ready to be processed further.
STAGE 2: Photolithography
After preparing the negative, the next stage is photolithography. The steps performed under
this are mentioned below.REMEMBER: All the processes for the manufacture of lith film are performed in the dark
room under minimal amount of light.
1. First of all we take a single sided copper clad board and cut it in size of the layout. 2. Clean it by metallic jute to see the shiny copper surface.
3. Now dip the PCB in the dip coating machine so that a layer photo resist material is coated on the PCB. Photo resist is an organic solution which when exposed to light of particular wavelength change their solubility in the developer. In dip coating copper clad board is clamped with the machine and when the machine is switched on the copper clad gets dipped in the material.
4. After a layer of photo resist material is applied on the board surface, we dry the copper clad in the oven at 50 .
5. The basic purpose of applying photo resist material is that when this material is subjected to the UV light, the circuit gets imprinted on the board.
6. Now the copper clad board along with the layout is placed in the UV light machine to get the imprint of the circuit. In this machine the laminated copper clad and the
negative film (lith film) kept in glass frame, for (2-3) minutes and after the time interval the circuit becomes partially visible on the board.
1919
STAGE 3: Etching
The next step after pre processing is etching The etching process is performed by exposing the surface of the board to an etchant solution which dissolves away the exposed copper areas other than the one deposited on the circuit .The different solutions used are: FeCl, CuCl, etc. CHROMATIC ACID, ALKALINE AMMONIA
STAGE 4: Drilling
Drilling is used to create the component lead holes in a PCB .The drilling can be done before or after the track defined for the components.
STAGE 5: Component Mounting And Soldering
It is the process in which components are mounted on the PCB with the help of soldering ion and soldering wire.
STAGE 6: PCB Testing
Each board needs to ensure that the required connections exist, that there are no short circuits and holes are properly placed .The testing usually consists of visual inspection and continuity testing.
19
8. APPLICATIONS
1. Street lights
2. Shadow alarm, Burglar alarm, Fire alarm 3. Garage door and car control systems 4. Other remote control systems
20
CONCLUSION
During the making of the project “LIGHT SENSOR” ,we developed a vast knowledge on working of IC’S ,LDR’s and concept of Relay.
We also studied and collected information on the various fields of implementations of the system. This project is very beneficial in today’s life as we worked on electronics
equipments.
The task was decided between the group members and every task was interrelated, so it was our duty to ensure that every one of us completed our task before moving to next step. This helped us to develop an understanding of the team work and the need to carry everyone along working for a group project.
References
Websites:
1. http://pecworld.zxq.net/Assets/SOURCE/PDF_fun_circuit/A ll_pdf_files_manual/20303_June05.pdf
2. www. datasheets catalog.com/ datasheets _pdf/N/.../ NE
555. shtml
3. http://en.wikipedia.org/wiki/Switch
Book:
Ramakant A. Gayakwad- “OP AMP and linear integrated circuits” 4th edition(2001), Page no.
