3.2 Input and Output Devices

Describe the physical structure of a 1D barcode and how it represents digits. [5 marks]

• It consists of dark and light parallel lines of varying thickness.

• It uses guard bars to separate the left and right sides.

• Each digit is made of two dark lines and two light lines.

• Left-side digits have an odd number of dark elements and right-side digits have an even number.

• This arrangement allows the barcode to be scanned in any direction.

Describe how a barcode scanner reads a barcode and converts it to digital data. [5 marks]

• An illuminator, such as a red laser or LED, shines light onto the barcode.

• The light is reflected back; white lines reflect light, while black lines reflect less light or absorb it.

• Sensors (specifically photoelectric cells) capture the reflected light.

• The pattern of reflections is converted into binary values or digital data.

• A microprocessor interprets the data.

Explain how a barcode scanning system operates to check for errors upon input. [4 marks]

• A check digit is calculated from the barcode data using an algorithm (such as Modulo 11).

• This check digit is added to the barcode.

• When scanned, the check digit is recalculated using the same algorithm.

• If the calculated check digit and the scanned check digit do not match, an error has occurred.

Explain how a barcode system manages stock in a supermarket. [6 marks]

• The barcode is used as a key field to uniquely identify and look up the product in the stock database.

• The stock level is automatically deducted or reduced by 1 each time it is scanned.

• The system continuously compares the remaining stock against a pre-set re-order level.

• If stock is less than or equal to this level, it triggers an automatic re-order.

• A flag is added to the record to stop duplicate re-ordering every time the item is read.

• Stock levels are updated in the database when new stock arrives.

State the advantages of using barcodes for both supermarket management and customers. [4 marks]

• Management: Faster to change prices centrally, Enables automatic stock control

• Customers: Results in faster checkout queues, reduces charging errors

State two applications of a barcode reader (excluding supermarket stock control) and describe how it is used in each. [4 marks]

• Libraries: Links books to borrowers automatically to check return dates.

• Airports: Scans boarding passes at check-in.

Describe three differences between a 1D Barcode and a Quick Response (QR) code. [3 marks]

• Barcodes are 1D (vertical lines) whereas QR codes are 2D (squares).

• QR codes can hold more data than barcodes.

• QR codes can be read from any angle and are more error-tolerant than barcodes.