Input Devices

Bar-Code

A bar-code is a set of parallel printed lines of differing thickness (usually alternately black and white) which represent a number - see the following picture:
 
Bar-codes are used on shop goods to identify the
product and to give a number code for the following:
• Country of origin.
• Manufacturer.
• An item number for the product.
Note. Prices change frequently and so they are not stored in bar-codes.
The price of an item is usually stored in the item's record in a stock file.
 
Methods of reading bar-codes:
A hand-held light pen or 'wand'
When the wand is passed over the bar-code it directs a narrow beam of light onto it,
and then measures the amount of reflected light so enabling the computer to
distinguish between the black and the white lines.
 
A stationary scanner
-When the item is passed over the scanner, a laser beam scans the bar-code and
measures the reflected light in much the same way as the light pen does.
Examples of the uses of bar-codes:
• On labels on shelves. These are used during stock-taking.
• On the labels of goods. These are used at EPOS/EFTPOS terminals to
identify goods.
• In libraries to identify books.

 Scanner

A scanner can be used to convert a picture into digital form so that it can be processed by a

computer and printed out. For example, a photograph could be scanned and incorporated into a wordprocessor or desktop publisher document.Like the light pen and the bar-code reader, a scanner measures the levels of reflected light and codes these into a digital signal which is processed by a CPU. There are various designs of scanner, e.g. some are hand-held

and others are flat-bed types. Some scanners produce only black and white pictures (with colours being represented by shades of grey) while others faithfully reproduce the original colours.

Video Digitiser

This device allows a video frame to be digitised and relayed to a computer for processing.Once the image of the video frame is held in a computer, it can be used in the same way as a scanned picture and incorporated into computer documents.

Digital Camera

A digital camera (as its name suggests) stores its data in digital form on its own internal memory and so there is no need to use a digitiser.The digital signal from the camera is sent through leads directly to the computer's serial port.