Topic 3 · Hardware
Input devices, output devices, and sensors
How common input and output devices work, and which sensor to pick for a job.
Input and output
An input device captures data from the outside world and turns it into binary for the computer. An output device turns binary from the computer into something people can see, hear, or touch, or into movement.
- 1Input deviceKeyboard, scanner, sensor...
- 2ProcessorProcesses the binary data
- 3Output deviceScreen, printer, speaker, actuator...
Input devices
| Device | How it works / what it is for |
|---|---|
| Barcode scanner | Shines light on the bars; black bars reflect less than white gaps. The pattern is turned into the product's number. |
| QR code scanner | A camera captures the 2D square pattern, which can store far more data than a barcode, such as a web address. |
| Digital camera | Light passes through a lens onto a sensor made of millions of light-sensitive pixels. |
| Keyboard | Each key press completes a circuit; the key's character code is sent to the computer. |
| Microphone | Sound vibrates a diaphragm, which creates an electrical signal that is sampled into binary. |
| Optical mouse | An LED lights the surface and a sensor tracks how the surface image moves. |
| 2D and 3D scanners | Light (2D) or lasers (3D) measure an object to create a digital image or 3D model. |
| Touch screen | Resistive: two layers are pressed together. Capacitive: a finger changes the screen's electric field. Infra-red: a finger breaks a grid of invisible beams. |
Output devices
| Device | How it works / what it is for |
|---|---|
| Actuator | A motor, valve, or pump that creates movement, controlled by a computer. |
| DLP and LCD projectors | Project a large image. DLP uses millions of tiny mirrors; LCD shines light through a liquid crystal panel. |
| Inkjet printer | Sprays tiny droplets of ink onto paper. Cheap to buy, good for photos. |
| Laser printer | Uses a laser, a charged drum, and powder toner. Fast and cheap per page for large volumes. |
| 3D printer | Builds a solid object layer by layer, often from melted plastic. |
| LED and LCD screens | Grids of pixels. LCD screens use liquid crystals with a backlight; LED screens light each pixel or use LEDs as the backlight. |
| Speaker | An electrical signal moves a coil and cone, which vibrates the air to make sound. |
Sensors
A sensor is an input device that measures a physical property and sends the reading to a computer. Sensors produce analogue data, which is converted to digital before processing. Match the sensor to what needs measuring:
| Sensor | Measures | Used in |
|---|---|---|
| Temperature | Heat | Central heating, greenhouses |
| Light | Brightness | Automatic street lights, phone screens |
| Infra-red | Heat / movement of bodies | Burglar alarms, automatic doors |
| Pressure | Force or weight | Burglar alarms, car tyres |
| Proximity | How close an object is | Parking sensors, phones near your ear |
| Moisture / humidity | Water in soil / in the air | Crop irrigation, greenhouses |
| Acoustic | Sound | Noise monitoring, voice control |
| Accelerometer | Acceleration and tilt | Phones rotating the screen, airbags |
| Gas | Levels of a gas such as CO₂ | Air quality, gas leak alarms |
| pH | Acidity | Water treatment, soil testing |
| Flow / level | Movement / height of a liquid | Water supplies, fuel tanks |
| Magnetic field | Changes in a magnetic field | Phone compasses, door sensors |
Exam tip. In an exam scenario, name the sensor and say what it measures in that context, for example "a moisture sensor measures how wet the soil is".
Key terms
- Input device
- Hardware that sends data into a computer.
- Output device
- Hardware that presents results from a computer.
- Sensor
- An input device that measures a physical property, such as temperature.
- Actuator
- An output device that causes movement, such as a motor or valve.
Check yourself
Which type of touch screen works by a finger breaking invisible beams?Show answer
Infra-red touch screen.
A school prints 2000 worksheets a day. Which printer suits it best, and why?Show answer
A laser printer: it is fast and has a low cost per page for large volumes.
Which sensor should a smart greenhouse use to decide when to water plants?Show answer
A moisture sensor in the soil.