Learning Objectives
- Describe how common input devices capture data.
- Select suitable input devices for given applications and justify choices.
- Explain the operation and uses of resistive, capacitive and infrared touch screens.
- Distinguish between two-dimensional and three-dimensional scanners.
- Compare direct data entry with manual keyboard entry.
Key Terms
- Input device
- Hardware used to enter data or control signals into a computer system.
- Barcode
- A machine-readable pattern that represents an identification number.
- QR code
- A two-dimensional pattern capable of storing data in horizontal and vertical directions.
- Optical mouse
- A pointing device that uses light and an image sensor to detect movement.
- Digital camera
- A device that uses an image sensor to capture photographs or video as digital data.
- Microphone
- A device that converts sound waves into an electrical signal for digital sampling.
- Touch screen
- A display surface that also detects the position of touch input.
- Resistive touch screen
- A touch screen that detects pressure when conductive layers make contact.
- Capacitive touch screen
- A touch screen that detects a change in an electrical field caused by a conductive object such as a finger.
- Infrared touch screen
- A touch screen that detects the interruption of a grid of infrared beams.
- 2D scanner
- A device that captures a flat document or image as a digital bitmap.
- 3D scanner
- A device that captures the shape and dimensions of a physical object to create a three-dimensional digital model.
Keyboard, Mouse, Camera And Microphone
A keyboard is suitable for entering text, numbers and commands. Pressing a key closes or changes an electrical circuit, allowing the keyboard controller to identify the key and send a code to the computer. Keyboard entry is flexible but can be slow and may introduce typing errors.
An optical mouse shines light onto a surface and repeatedly captures small images. A processor compares successive images to determine direction and distance of movement. Buttons and a scroll wheel provide additional input. It is suitable for controlling a pointer in a graphical user interface but requires a usable surface and may not be ideal where space is limited.
A digital camera focuses light onto an electronic image sensor. The sensor measures light for a grid of pixels and the values are processed into a digital image or video frame. A microphone converts sound waves into an analogue electrical signal, which is sampled and converted into digital values by an analogue-to-digital converter.
Barcode And QR Code Scanners
A barcode scanner directs light at a printed barcode and detects the reflected pattern from dark bars and light spaces. The pattern is decoded into an identification number. That number is normally used as a key to look up a record in a database, such as a product record containing description and price.
A QR scanner, often implemented using a camera, captures a two-dimensional code. Software locates the code, corrects its orientation and decodes the pattern. QR codes can hold more data than traditional one-dimensional barcodes and can be read from different angles. They are used for web links, tickets, payments and product information.
Both devices reduce manual data entry. The code should usually identify a record rather than contain all changing information. For example, storing a current price directly in a printed barcode would make price changes difficult.
Resistive, Capacitive And Infrared Touch Screens
A resistive screen has flexible conductive layers separated by a small gap. Pressure causes the layers to touch, and the controller calculates the position from the electrical change. It can be operated with a finger, gloved hand or stylus, but repeated pressure can reduce clarity or cause wear.
A capacitive screen maintains an electrical field across the surface. A conductive finger changes the field, and sensors calculate the touch position. Capacitive screens support light touch and multi-touch gestures and are common in smartphones and tablets. Ordinary gloves or non-conductive styluses may not work unless specially designed.
An infrared screen places emitters and detectors around the edge to form a grid of invisible beams. A finger or object interrupts beams, allowing the controller to locate the touch. The display surface does not need a pressure-sensitive overlay and many objects can activate it, but dust, blocked edges or accidental interruptions may cause errors.
Two-Dimensional And Three-Dimensional Scanning
A 2D scanner moves a light source and sensor across a flat document. Reflected light is converted into pixel colour values, producing a bitmap image. Optical character recognition software may then analyse printed characters and convert them into editable text, although recognition errors are possible.
A 3D scanner measures points on the surface of a real object. It may use lasers, structured light or multiple images. The resulting set of points is processed into a digital model describing shape and dimensions. Applications include reverse engineering, medical modelling, preservation and creating objects for 3D printing.
The correct device depends on the data required. A flat paper photograph requires a 2D scanner. A replacement component requiring accurate shape and depth requires a 3D scanner.
Common Input Devices And Suitable Uses
| Device | How Data Is Captured | Suitable Use | Reason |
|---|---|---|---|
| Keyboard | Key presses are converted into codes. | Entering an essay. | Flexible for large amounts of text. |
| Optical mouse | Successive surface images reveal movement. | Selecting and dragging graphical objects. | Provides precise pointer control. |
| Digital camera | Image sensor records pixel light values. | Capturing photographs or video. | Directly records visual scenes. |
| Microphone | Sound signal is sampled and digitised. | Voice recording or speech input. | Captures sound directly. |
| Barcode scanner | Reflected bar-and-space pattern is decoded. | Retail product identification. | Fast and reduces typing errors. |
| QR scanner | Camera captures and decodes a 2D pattern. | Tickets, links or payment identifiers. | Stores more data and reads from varied angles. |
| 2D scanner | Reflected light from a flat page becomes pixels. | Digitising documents. | Produces a detailed image of a flat original. |
| 3D scanner | Surface points and depth are measured. | Creating a model of a physical object. | Captures three-dimensional shape. |
Touch-Screen Technologies
| Technology | Detection Method | Advantage | Limitation |
|---|---|---|---|
| Resistive | Pressure makes conductive layers touch. | Works with many objects and gloves. | Requires pressure and surface layers can wear. |
| Capacitive | Conductive touch changes an electrical field. | Responsive and supports multi-touch. | Ordinary gloves or non-conductive objects may not work. |
| Infrared | Touch interrupts beams around the screen. | Any opaque object can activate it and image remains clear. | Blocked edges, dust or accidental objects can interfere. |
Worked Examples
Selecting A Device For A Supermarket
Question: Explain why a barcode scanner is more suitable than a keyboard for entering product identifiers at a checkout.
- The printed code can be read directly.
- Scanning is faster than typing a long identifier.
- It reduces transcription errors.
- The identifier can be used to retrieve price and stock data from a database.
Answer: A barcode scanner gives faster, more accurate direct entry of the product code and supports automatic database lookup.
Choosing A Touch Screen
Question: A factory terminal must be used by workers wearing thick gloves. Which touch-screen technology is suitable and why?
- A normal capacitive screen may not detect non-conductive gloves.
- A resistive screen responds to pressure from a gloved finger or stylus.
- An infrared screen can also detect an opaque gloved hand.
- Environmental conditions and required accuracy should be considered.
Answer: A resistive or suitable infrared screen is preferable; resistive is a clear choice because pressure from the glove can make the layers contact.
Examination Guidance
- When selecting an input device, connect one feature directly to the application’s needs.
- For barcode questions, explain that the code often identifies a database record rather than containing the price itself.
- Learn the physical detection principle for all three touch-screen technologies.
- Do not call a QR code a one-dimensional barcode; it stores data in two dimensions.
- Distinguish a 2D image scan from a 3D model containing shape and depth information.
Common Mistakes
- Listing an input device without justifying why it suits the application.
- Saying an optical mouse measures movement using a rolling ball.
- Claiming a microphone stores sound without analogue-to-digital conversion.
- Confusing capacitive touch with pressure-based resistive touch.
- Saying a 3D scanner prints an object; printing is an output process.
Knowledge Check
1. How does an optical mouse detect movement?
2. Why is a barcode normally linked to a database?
3. How does a resistive touch screen detect input?
4. What is a major advantage of a capacitive touch screen?
5. What additional information does a 3D scanner capture compared with a 2D scanner?
