Saturday, March 9, 2013

Other Input Devices

Other Input Devices

Other Input Devices

VOICE RECOGNITION

Method

Using a microphone (or a telephone handset) human speech is coded into a sequence of electrical signals. The computer being used searches a set of stored patterns for the sound which has been input.

Advantages of voice recognition

1 No typing or data preparation is necessary.

2 It can be used remotely by telephone, or by those who are handicapped or who have their hands occupied.

Disadvantages

1 At present the method does not give good results. Relatively few words can be recognized and the error rate is high.

2 Recognition is slow.

3 It is not suitable in noisy places without a shielded mouthpiece.

Uses

1 Where only a few different commands are to be given and the hands cannot be used, for examply by a helicopter pilot to produce a display of the appropriate instruments on a screen, using simple prestored voice commands.

2 Over the telephone, for example by a bank. The computer can recognize a caller from a spoken code, tell him/her the state of a requested account ( by synthesized voice ) and accept simple commands such as 'repeat'.

3 By handicapped people to control equipment..

DIRECT INPUT FROM INSTRUMENTS

Many measuring devices are now digital and electronic and can be linked to a computer. This requires special software to make use of the data coming in and, usually, a special interface between the device and the computer.

Examples of direct input

1 Thermostats or thermometers connected to a computer controlling a heating system.

2 A pressure pad on a road connected to a computer controlling traffic lights.

3 The instruments in a space vehicle interfaced with a computer which calculates the flight path and controls the rockets.

Comparison of Input Methods

Note: Speeds are in characters per second unless otherwise stated, and refer to the rate at which the input device transfers data to the central processing unit.

Input device

Medium

Preparation method

Verification method

Typical input speeds

Disc unit

Magnetic discs

Typed at key station

Retyping at same station

100000 to 2000000

Tape drive

Magnetic tape

Key to tape or pooled from key to-disc station

As disc or by rewinding tape

150000

Floppy disc unit

Floppy disc

Separate key station

Retyping at same station

20000

Magnetic tape

Magnetic tape

Separate key- station

Retyping at same station

Cartridge 2000 to 1 000000;

Cartridge/

cassette unit

cartridge or

cassette

cassette 2000

to 20000

OCR device; document reader

Document

Handprinting or typing or computer printer or OCR encoder

Checked by eye

1 to 40 documents per second

MICR

device

Document

(cheque)

MICR encoder

Not

applicable

15 documents

per second

Mark sense

reader;

optical mark

reader

Marked card

or document

Making pencil

marks in pre-

printed. ovals or

rectangles

Difficult to

verify

15 to 600

documents per

Minute

Fig 17 Comparison of input methods