Input Devices

An input device is any piece of computer hardware that allows a user or external environment to enter data, commands, and signals into a computer system for processing.

Learning Objectives

• Identify and describe the operation of manual and automatic input devices.
• Choose a suitable device for the data being captured.
• Explain keyboard, mouse, scanner, camera and microphone operation.

Common Input Devices

1. Barcode Scanners and QR Code Readers

• 1D Barcodes: A series of parallel alternating black and white lines of varying widths.
• A red LED or laser reflects light off the barcode; white spaces reflect high light while black bars absorb light.
• A photodiode detects the reflected light patterns and converts them into digital binary digits representing the product code.
• 2D Quick Response (QR) Codes: A matrix of dark squares on a light background.
• Can store significantly more data than 1D barcodes (thousands of characters including URLs, plain text, and contact information).
• Built-in alignment markers in three corners allow scanning from any angle.
• Built-in Reed-Solomon error correction allows decoding when some data is damaged; the recoverable amount depends on the error-correction level and damage pattern.

2. Digital Cameras

• Light passes through a lens onto an array of light-sensitive sensors (a CCD or CMOS image sensor).
• Each sensor cell converts light photon intensity into an electrical charge.
• Colour filters (Red, Green, Blue) separate the light into colour components.
• An ADC converts these charges into digital pixel values and stores the photo on solid-state flash memory.

3. Microphones

• Sound waves vibrate a flexible diaphragm.
• The diaphragm's movement induces a varying electrical analogue voltage signal.
• The analogue signal is fed into an ADC (Sound Card), which samples the wave and outputs binary audio data.

Keyboard, mouse and scanners

A keyboard detects a pressed key and sends its code to the computer. An optical mouse illuminates a surface, captures repeated images and compares them to detect movement; buttons supply selection input.

A 2D scanner illuminates a document and detects reflected light to produce a digital image. OCR is separate software that can turn suitable image content into editable text. A 3D scanner measures a physical object's surface from different positions to build a model containing depth as well as width and height.

Worked choice

To archive a paper receipt faithfully as an image, choose a 2D scanner. To measure a sculpture's surface for a 3D model, choose a 3D scanner. A barcode reader retrieves the encoded identifier, not a full page image or 3D shape.