PC Computer Hardware Input Devices Part 2

DIGITIZER

A digitizer is an input device that converts graphic and pictorial data to digital (binary) form which can be direct fed and stored inside a computer. There are two types of digitizers: rectangular- coordinate or flatbed digitizer and image- scan digitizer. In case of a flatbed digitizer, the drawing to be digitized is spread and fixed over a rectangular flatbed table. A mechanism is now moved over the surface of the drawing that scan the drawing and produces signals related to X and Y coordinates of the table. Image scan digitizers scan and reproduce entire drawing and photographs automatically. They are costlier and more powerful than the flatbed digitizers and are capable of digitizing not only the shape and size of the drawing but also the varying intensities on a gray to black scale at different points of the drawing. Thus, flatbed digitizers are mainly use to digitize simple drawing, graphs, charts, etc. and image- scan digitizers are used to digitize more complex pictures and photographs.

VOICE RECOGNITION SYSTEM

This is an input device; consist of a microphone or telephone that converts human speech into electrical signals. A signal pattern obtained in this manner is transmitted to the computer where it is matched against pre stored patterns to identify the input. When a close match is found, a word is recognized by the system. T he set of pre stored patterns is known as the vocabulary of the system. T o build up this vocabulary, the system has to be trained to recognize the words and phrases that are to present in the vocabulary. Hence the system is initially operated in a “training mode “when the user speaks the words and phases (to be sorted in the vocabulary) several times to train the system to recognize his / her particular voice pattern. In this mode, the patterns are created and stored for future matching. Because the accent of different speakers varies, most recognize system, are speaker dependent. How ever, a system may be trained to recognize the voice of more than one operator in which case a different vocabulary is maintained for each operator. These systems are used where a person wants to input data to a computerized system in situations where his hands are busy, or his eyes must be fixed on a measuring instrument or some other object.

OPTICAL MARKS READER (OMR)

It is a device for checking the documents and question papers. Now a days it is quite a common practice to the knowledge and IQ level of candidate by multiple choice objective type questions. The candidates are required write there answer by putting a standard dot in front of the correct answer with help of specially designed soft pencils. While evaluating the answer paper , OMR directs a thin beam of light is transmitted through the dot as compared to nearby surface due to which answer is recognized by the computer.. The OMR can evaluate only those documents which are printed with marked positions in the specified areas. OMR can read about 10,000 document per hour, and thus can print the result within the same day without any favoritism or mistake.

OPTICAL CHARACTER READER (OCR)

This is also a device for reading the documents. It can read alphanumeric characters created in a particulars style or good quality paper using special ink. The shape of character is recognized by OCR with help of light source in conjunction with photo electric cells. Optical characters are being extensively used for billing purposes, i.e. preparation of electricity bills and insurance premium renewals.

BAR CODE READERS

This method uses a number of bars (lines) of varying thickness and spacing between them to indicate the desired information. Bar code reader can read such bars and converts them into electrical pulses to be processed by a computer. The most common used bar code is Universal Product Code (UPC). The UPC code uses a series of vertical bars of varying width. These bars are detected as ten digits. The first five digits identify the supplier or manufacturer of item. The second five digits identify individual product code. The code also contains a check digit to ensure that the information read is correct or not.

MAGNETIC INK CHARACTER READER (MICR)

It uses a special ink that can be magnetized so that the individual characters can be recognized by the reader from the shape of the wave form of the electrical pulses induced in the magnetism. Such a system uses special inks containing magnetic particles of iron oxide. The characters are printed in a very distinctive style. When such documents are passed through a strong magnetic field, the ink coded characters become magnetized. MICRs have got reading speed about 24000 documents per minute. Such a character recognition system is now being used by all commercial banks even in India a MICR coded cheque.