GCSE Computer Science/Input devices
- Describe the principles of operation (how each device works) of these input devices: 2D and 3D scanners, barcode readers, Quick Response (QR) code readers, digital cameras, keyboards, mice, touch screens, interactive whiteboard, microphones
An input device is a hardware device, often a peripheral device, which is used as part of a computer system. Input devices allow a computer system to receive data from the real world. For instance a microphone can be used to input audio data in to a computer system.
There are many different kinds of input device, some of which are described below:
2D and 3D Scanners
Scanners use light to make digital copies of real world objects. 2D scanners are usually used to make digital copies of documents or pictures, but can also be used to create a 2D image of other objects as well. In a flat bed scanner the document is placed on a glass plate. A light is then shone on the piece of paper and a light sensor used to detect the light which is bounced back. Wand scanners, also known as hand-held scanners, work on the same principal except that the user will move the scanner across the document manually. They can be used in conjunction with a printer to create copies of documents.
3D scanners use reflected laser light to build up a three-dimensional model of an object. They can be used in conjunction with 3D printers or fabricators to duplicate objects.
A barcode reader works in a very similar way to a 2D scanner. It uses reflected light from a laser to detect the black lines in a barcode or QR code. All barcodes use a check-digit so that the system knows when a barcode has been scanned correctly. Usually barcode scanners will emit a beep sound once a barcode has been scanned and confirmed as correct by checking the check-digit. They are often integrated in to electronic point of sale (EPOS) systems in supermarkets and stores. They are also frequently used in libraries for checking books in and out. They have applications in manufacturing to track the progress of items through the assembly line or in courier services to track packages from source to destination.
Digital cameras work in a very similar way to traditional cameras except that the images are self-processed and then saved digitally on some type of storage media, usually flash memory, rather than by exposing light to photosensitive film which is later processed in a lab.
Digital and film cameras share an optical system, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The diaphragm and shutter admit the correct amount of light to the imager, just as with film but the image pickup device is electronic rather than chemical. However, unlike film cameras, digital cameras can display images on a screen immediately after being recorded, and store and delete images from memory. Many digital cameras can also record moving videos with sound. Some digital cameras can crop and stitch pictures and perform other elementary image editing.
Digital cameras can also capture video. Webcams in particular are popular devices for this and are designed with use over the Internet in mind.
A keyboard is the most commonly used input device on personal computers. It consists of a number of keys arranged in the style of a typewriter. Each key, when pressed, operates a switch which closes an electronic circuit. This then sends an electrical signal to the CPU. Each key press sends a unique signal so that the CPU knows which key was pressed.
They keys have a letter, number or symbol printed or engraved on it so that the user knows which keys to press. Pressing keys can be used either for data entry or to initiate certain commands (such as the print-screen key). Often multiple keys need to be pressed simultaneously to achieve a desired effect. For instance pressing the Ctrl and C keys together is often used to copy the selected content to the clipboard.
A mouse is a device used to control the motion of an electronic pointer on the computer screen. The pointer is used to select objects on the screen and is usually used to control the functions of software. Early mice used a rollerball connected to wheels. When the mouse was moved in a particular direction the corresponding wheels were then moved which could be detected and translated into motion. More modern optical mice instead us a laser directed underneath the mouse to detect its motion.
Graphics pads are also available, which also control the movement of an on-screen pointing device. These instead work with a special pen, or stylus, which is detected as it moves across a tablet style surface.
A touch screen is like a regular display screen except that it can also respond to the touch of either a finger or a stylus. They are commonly used as the primary input device for tablets, mobile phones and interactive displays. There are a variety of different techniques used to make them work. One common technique involves the use of electrically charged surfaces. When the surface is pressed with a finger or stylus the resistance across the surface changes in such a way that the location of the touch can be detected.
An interactive whiteboard works like a large graphics tablet, except much larger and usually used in conjunction with a projector to overlay the user's screen on to the device's surface. Some boards are used with a stylus in the same way as a graphics tablet, others can be used by touching the surface with a finger. They can be wall-mounted or can be mounted in a portable frame.
Interactive tables are the same as interactive whiteboards but laid horizontally and positioned as a table rather than positioned vertically.
A microphone is used to capture sound waves, which are then converted to a digital format for processing and storage by a computer system. They are often built-in to modern computing devices, such as laptops, mobile phones and tablets. They can also be external devices connected via cable or wirelessly.
Most microphones today use electromagnetic induction (dynamic microphones), capacitance change (condenser microphones) or piezoelectricity (piezoelectric microphones) to produce an electrical signal from air pressure variations. Microphones typically need to be connected to a preamplifier before the signal can be amplified with an audio power amplifier or recorded.
- Describe how a range of sensors can be used to input data into a computer system, including light, temperature, magnetic field, gas, pressure, moisture, humidity, pH and motion