22-05-2013, 03:47 PM
Optical Mark Reading Scanner
Optical Mark.docx (Size: 2.7 MB / Downloads: 40)
INTRODUCTION
The objective type examinations are now conducted for entrance into many professional courses and jobs. Candidates sit through these examinations in large numbers. Manual checking of these papers is not only time consuming but can also lead to erroneous marking. To overcome this problem, we are developing an answer paper evaluator.
Students record their answers to MCQ on a machine readable answer sheet. These sheets are fed through an Optical Mark Reading Scanner. The OMR allows automated data entry that turns pencil marks into useable computer information. If two or more circles are filled in on the answers sheet, or the correct answer is carelessly marked, the question will be marked `wrong’. Specially written software controls the test scoring and analysis. The software analyses the students’ answers to product the Test Scoring and Analysis output.
OMR is the scanning of media to detect the presence or absence of a mark in a specific position. It is widely used in surveys, assessments and evaluations. The multiple choice answer sheet and course evaluation forms are daily examples utilizing OMR technology.
NECESSITY
The present day OMR scanning machines are very expensive and require a high initial investment. This makes it unsuitable for smaller applications like placement exams, objective entrance exams etc.
This problems gives rise to the need of our project which is low cost and high accuracy. This system will be used in our TRAINING AND PLACEMENT cell for placement exam evaluation. This system is designed to be convenient and simple in use for a broad class of people. Thus this system can be operated by students also and requires no prior training.
OBJECTIVE
This project is aimed to reduce the price of the conventional OMR based exam paper evaluator. The price of this project is low as compared to the market price of prefabricated OMR system which cost up to Rs.70000/-. This reduced price enhances its application to collage level tasks like objective exams, placement exams etc. Moreover the simplicity and convenience to use this project makes it extremely user friendly. This project requires high accuracy and average execution time. Hence, this project suffices the basic need for average processing time and high reliability.
THEME
The project consists of IR sensors which are moved on the answer sheet to detect the answers provided by the candidate. The IR sensors provide a cheap but effective way to replace the conventional high priced optical sensors used in branded OMR machines. The use of Micro Controllers simplifies the cumbersome task of data transfer via Rs.232 serial port communication. The Microcontroller used is 89C51. The stepper motor is used to drive the IR sensor assembly on the answer sheet. An additional accessory of LCD display is provided to make the project more users friendly.
ORGANIZATION
The basic need of our Training and Placement cell was accurate and time saving solution for checking the large quantity of MCQ answer sheets. This application required a low costing highly accurate and reliable solution. By replacing the conventional optical scanners by IR sensors the use of `trans optic’ paper can be avoided. Hence our project is aimed to counter this problem and come up with a solution compatible to the need of our college’s need for the Training and Placement cell.
BACKGROUND
Many traditional OMR devices work with a dedicated scanner device that shines a beam of light onto the form paper. The contrasting reflectivity at predetermined positions on a page is then utilized to detect the marked areas because they reflect less light than the blank areas of the paper.
Some OMR device use forms which are preprinted onto `trans optic’ paper and measure the amount of light which passes through the paper, thus a mark on either side of the paper will reduce the amount of light passing through the paper. In contrast to the dedicated OMR device, desktop OMR software allows a user to create their own forms in a word processor and print them on a laser printer. The OMR software then works with a common desktop image scanner with a document feeder to process the forms once filled out.
HISTORY
Optical mark recognition (OMR) is the scanning of paper to detect the presence or absence of a mark in a predetermined position. Optical mark recognition has evolved from several other technologies. In the early 1800’s and 1900’s patents were given for machines that would aid the blind.
OMR is now used as an input device for data entry. Two early forms of OMR are paper tape and punch card which are actual holes punched into the medium instead of pencil filled circles on the medium. Paper tape was used as early as 1857 as an input device for telegraph. Punch cards were created in 1890 and were used as input devices for computers. The use of punch cards declined greatly in the early 1970’s with the introduction of personal computers. With modern OMR, where the presence of a pencil filled in bubble is recognized, the recognition is done via an optical scanner.
BLOCK DIAGRAM DESCRIPTION
SCANNER
The filled answer sheet provided by the student after an objective exam is fed the scanner assembly of the project. The scanner block consists of a series of ten LEDs which are placed in such a way that they check the required number of answers. The Scanner head which moves vertically along the axis of the paper is driven by the stepper motor. The answers detected by the receivers (Rx) are fed to the comparators. The output of the this block is then is provided to the microcontroller (89s52). The spacing between the paper and the sensors is about 5mm. This small distance is required for the high sensitivity of the optical reader.
STEPPER MOTOR
The mail function of this block is to drive the scanner head. The step angles are thus decided in accordance to our spacing in the answer sheet. The movement of the scanner head is in the vertical direction and its mail function is to place the sensors directly on top of the answer bubbles. The answers provided by the students is then detected by the sensors and the stepper motor places the sensor head again to the initial position for the next paper to be checked.
STEPPER MOTOR DRIVER
The digital system and the microcontroller lack the sufficient current to drive the relay. While the relays coil need around 10mA to be energized, the microcontroller pin can provide a maximum of 1-2mA current. For this reason, we place a driver such as the L298 between the microcontroller and the relay. Thus we can say that this block is used as an device that is used for providing sufficient amount of current shich will drive the stepper motor.
MICROCONTROLLER
The microcontroller block is te heart of our project. It accepts the voltage level from the scanner block and compares it with the option provided by the examiner. The correct series of option provided via the software console. The bubble which is darkened generates a certain through the comparators is provided to the microcontroller. Another major task of the microcontroller is to drive the stepper motor. But since the voltage level at the microcontroller’s output is very less we use a driver. The series of correct answers is stored in the memory of the microcontroller block. The result of the comparison is given to the next block i.e. computer. This input is then computed upon and the result is generated. The generated result i.e. number of correct and incorrect answers is displayed on the LCD.
SOFTWARE CONSOLE
This block is used to determine the number of questions the student is going to face in the examination. The software also gives us the provision of storing the exam result according to roll number and the name. The correct answers are fed by the examiner into the memory of the microcontroller block according to which the answers will be evaluated. The compared correct and incorrect answers are then properly arranged and displayed along with the score of the respective student. The software console consists of a database where the result of every student appearing for the exam is stored. This information can be used in the future for analysis and grading.
PCB LAYOUT AND ARTWORK DESIGN
A PRINTED CIRCUIT BOARD is popularly known as the first thing we would require when we decide to build an electronic circuit. A roper PCB ensures that various components are interconnected as per the circuit diagram, once they have been placed on the PCB and subsequently soldered. PCB design and fabrication techniques have undergone so much of development that it has become a subject itself.
Double sided PCB, multilayer PCB with PTH (plated through holes), using CAD software design for PCB layout design, flexible PCB’s etc are only some of the developments.
An average experimenter however needs to go into the details of these technologies or is supposed to learn the intricacies of the art of PCB layout designing.
What he needs familiarization with different steps involved in PCB fabrication particularly the etching process so that he can make his own PCB economically from an available PCB layout design.
ETCHING
In the etching process,all excess copper is removed leaving behind only the painted pattern. To do etching, the painted PCB board laminate is placed in a flat tray with the copper side facing upwards.an aqueous solution of ferric chloride with the quantity depend on the size of PCB.
The PCB to the etched is then pourd in the tray.The PCB should be fully immersed in the ferric chloride sol. The sol is prepared by adding abt.40-50 grams of ferricchloride of 100ml of warmwater. The sol. Should be nicely stirred and a few drops of HCL are added to speed up the etching process.The tray can be moved up and down. The etching process may take abt. Half an hour to one hour.
The etching tjme again depends on the size of PCB and area to be etched.it must the PCb is neither under etched nor over etched.If the PCB is kept immersed in the sol. After etching is completed, the sol.is likely to be penetrating the copper portion that is require to be preserved and cause more etching.
The ferric chloride should be preserved in the bottle for future use and should not be wasted.sol.once made can be used for 3-4 etchings. The laminate is thoroughly wasted in water etching is completed.the paint is removed with alcohol or thinner.
DRILLING – TINNING
The next major operation after etching is drilling and tinning,the diameter of hole varies from component to component.it is 0.8mm for IC pins,1mm to 1.25mm for resistors and capacitors,1.5mm for diodes and presets. The size of holes for the resistors would also depend on wattage of resistor.
The oxidation of copper portions can be prevented by either tinning that can be done by using soldering iron or by giving a coat of some insulating varnish.