IGCSE Computer Science 0478 — 3.2 Input and Output Devices Hangman

The 51 key terms

1input, process, store, output

A digital system takes in data (input), works on it (process), keeps it (store) and shows a result (output).

2input device

A piece of hardware, like a keyboard, mouse, microphone, camera, scanner, sensor or touchscreen, that sends data into a digital system.

3keyboard

An input device where pressing a key completes a circuit. The controller identifies the key and sends its character code to the computer, so text and commands can be entered.

4optical mouse

An input device with an LED or laser under it that lights the surface while a sensor takes rapid images to track movement and move the pointer. It has no ball.

5microphone

An input device that turns sound waves into an analogue electrical signal, which an ADC converts to digital data so the computer can record or process voice.

6digital camera

Input device: a lens focuses light onto an image sensor of light-sensitive cells; each cell becomes a pixel of digital data, stored as an image file. More pixels give more detail.

7barcode scanner

An input device that shines a laser across a barcode. Black lines absorb light, white gaps reflect it, and a sensor reads the pattern to get the product number.

8QR code scanner

Uses a camera to capture a 2D square grid of black and white modules and decodes it into data like a web address or text. It holds more data than a barcode and reads from any angle.

91D barcode vs 2D QR code

A barcode stores a short number in one dimension of lines; a QR code stores much more data in two dimensions of squares and can be read by a camera from any angle.

10touch screen

A display that is also an input device: it detects where a finger or stylus touches it. Types are resistive, capacitive and infra-red. Used in phones, tablets, kiosks and ticket machines.

11resistive touch screen

A screen with two conductive layers that touch when pressed; the change in resistance at the touch point gives its position. Works with finger, glove or stylus.

12capacitive touch screen

A touch screen with a charged glass layer. A finger conducts electricity and changes the charge at the touch point, so its position is found. Supports multi-touch.

13infra-red touch screen

A screen with a grid of infra-red beams across it. A touch breaks beams, and the broken x and y beams give the touch position. Works with any object.

14resistive, capacitive, infra-red

Resistive senses pressure on layers; capacitive senses a finger's electric charge; infra-red senses a broken light beam. How touch is detected decides which device each suits.

152D scanner

An input device that moves a light and sensor across a flat page or photo, reading the reflected light to capture a digital image made of pixels.

163D scanner

An input device that uses lasers, light patterns or cameras to measure many points on an object's surface and combine them into a digital 3D model of its shape.

17suitable input device

The input device that best captures the data needed and suits the user's situation. Justify it with 'because'. E.g. a microphone because it captures sound.

18output device

A piece of hardware that shows or gives the results of processing to the user, such as a monitor, projector, speakers, headphones or printer.

19LCD screen

Screen with a backlight shining through liquid crystals that twist to block or pass light. Red, green and blue filters on each pixel make its colour.

20LED screen

A screen that uses light emitting diodes as its light source, as a backlight for an LCD panel or as the pixels themselves. It is bright, thin and uses little power.

21LCD vs LED

LCD screens use a fluorescent (CCFL) backlight; LED screens use LED backlights, so they are brighter, thinner, have better contrast and use less power.

22LCD projector

An output device: a bright lamp shines light through red, green and blue LCD panels that form the image, then a lens focuses the recombined light onto a screen.

23DLP projector

A projector with a chip of tiny mirrors (one per pixel) that tilt towards or away from the lens to make the image. A spinning colour wheel adds colour.

24LCD vs DLP

Both projectors show an image on a screen. LCD shines light through liquid crystal panels; DLP bounces light off tiny mirrors (micromirrors). They differ in sharpness, colour, size and cost.

25Inkjet printer

Sprays tiny droplets of liquid ink through nozzles in a print head onto paper as the head moves across it. Uses cyan, magenta, yellow and black cartridges.

26laser printer

A printer that uses a laser to draw the image as static charge on a drum. Toner sticks to the charged areas, is transferred to paper, then fixed by a heated fuser.

27inkjet vs laser

Inkjet sprays liquid ink: good photo quality, cheap to buy, costly per page. Laser fuses toner powder: fast, sharp text, dearer to buy, cheaper per page.

283D printer

An output device that builds a solid object from a digital 3D design file by adding material, such as melted plastic, one thin layer at a time.

29speaker

An output device that turns an electrical signal into sound. An electromagnet makes a cone vibrate, and the vibrations make sound waves. A DAC first converts digital sound to analogue.

30actuator

An output device that turns a control signal from a processor into physical action, such as a motor turning, a valve opening or a heater switching on, in control systems and robots.

31suitable output device

Match the result needed (image, print, sound, 3D, movement) and the situation to the device that suits it best, then justify with 'because'.

32sensor

An input device that measures a physical quantity, such as heat or light, from the environment and sends the readings to a computer or microprocessor.

33ADC (analogue-to-digital converter)

Turns the continuously varying analogue readings from a sensor into digital values (binary numbers) so a computer can process them.

34acoustic sensor

A sensor that detects sound and measures its level. Used in noise monitoring, burglar alarms and glass-break detection to show how loud a sound is or whether a sound is present.

35accelerometer

A sensor that measures acceleration (change in speed or direction) and tilt. Used for phone screen rotation, step counters and car airbag impact detection.

36flow sensor

An input device that measures how much liquid or gas moves past a point in a set time (the flow rate). Used in water meters, fuel systems, pipelines and irrigation.

37gas sensor

An input device that detects the presence or concentration of a particular gas in the air, e.g. in carbon monoxide alarms, gas leak detection, air quality checks and breathalysers.

38humidity sensor

An input device that measures the amount of water vapour (moisture) in the air. Used in weather stations, greenhouses and air conditioning systems.

39infra-red sensor

A sensor that detects infra-red radiation, such as heat given off by people and objects, or a broken infra-red beam. Used in burglar alarms and automatic doors.

40level sensor

A sensor that measures how full a container is by detecting the height of a liquid or solid, e.g. in a water tank, fuel gauge or chemical vat.

41light sensor

An input device that measures how bright the light is and sends the light level to a computer. Used in automatic street lights, screen brightness and greenhouses.

42magnetic field sensor

An input device that detects the presence and strength of a magnetic field. Used in door alarms, compasses, wheel speed counters and metal detectors.

43moisture sensor

An input device that measures the amount of water in a solid material such as soil. Used in automatic plant watering and farming. Not the same as a humidity sensor, which measures air.

44pH sensor

An input device that measures how acidic or alkaline a liquid is on the pH scale and sends the pH value to a computer. Used in water treatment, fish tanks, soil testing and food production.

45pressure sensor

An input device that measures the force applied over an area by a gas, liquid or solid, e.g. in tyre pressure monitors, weather forecasting and pressure pads.

46proximity sensor

A sensor that detects whether an object is nearby, or how far away it is, without touching it. Used in parking sensors, phones turning off the screen during calls and automatic doors.

47temperature sensor

An input device that measures how hot or cold something is. Used in central heating, ovens, greenhouses and weather stations.

48feedback loop

A sensor sends readings to a microprocessor, which compares them with a stored value and signals an actuator, such as a heater, to act. This repeats continuously.

49data first, then sensor

Each sensor captures one type of data, so identify the data first (e.g. moisture in soil, humidity in air), then name the sensor that measures it.

50suitable sensor

The sensor that measures the physical quantity a system needs, e.g. light for street lamps or pressure for a car park. Justify it with 'because'.

51inputs and outputs

A complete system uses input devices or sensors to capture data and output devices or actuators to deliver results, each chosen to suit the task.