3.5 Input & Output Devices Trainer
Every input device, output device, and sensor Cambridge tests — plus how sensors work in automated systems.
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What do I need to know before I start?
Input devices send data into a computer; output devices present the processed results. Sensors are input devices that capture data from the environment. The big exam topic is the automated system sequence: a sensor sends data to a microprocessor, which compares it to a stored value and sends signals to actuators. Cambridge tests this full sequence — every step, in order, with exact vocabulary — so learning the chain matters as much as the definitions.
By the end of 3.5 you can…
| Objective | Why it matters |
|---|---|
| Define input device, output device and sensor precisely | Definitions are asked every year — exact vocabulary required. |
| Explain the role of a sensor in an automated system | s25/s23/s22 mark schemes all test the full sensor scenario sequence. |
| State that analogue sensor data is converted to digital (ADC) | s22 mark scheme: "analogue signal is converted to digital" — a standalone mark. |
| Describe the microprocessor comparing data to a stored value | s22/s23/s25 mark schemes: "compares data to a stored value" — exact wording. |
| Explain what actuators do | Actuators carry out the physical action (open a valve, switch a motor) in response to the microprocessor. |
| Give correct examples of input, output and sensor devices | Naming the right device type is commonly worth marks. |
Cambridge-approved terms
Hardware that sends data into a computer. Examples: keyboard, mouse, microphone, scanner, sensor.
Hardware that presents processed results. Examples: monitor, printer, speaker, actuator.
An input device that captures physical data from the environment (temperature, light, motion, etc.).
A component that carries out a physical action (motor, valve, heater) on a signal from the microprocessor.
Analogue-to-Digital Converter — turns a sensor's analogue signal into digital data the computer can process.
The pre-set value the microprocessor compares sensor readings against to decide what to do.
The automated system sequence
| Step | What happens |
|---|---|
| 1 | The sensor captures data from the environment (e.g. temperature). |
| 2 | The analogue signal is converted to digital by an ADC. |
| 3 | The microprocessor compares the reading to a stored value. |
| 4 | If the reading is outside the set range, the microprocessor sends a signal to an actuator. |
| 5 | The actuator carries out a physical action (e.g. switches on a heater). |
| 6 | The sensor keeps sending readings, so the process repeats continuously. |
Traps that cost marks every session
The sensor only captures data. The microprocessor compares it to the stored value and makes the decision.
Sensor data is analogue; it must be converted to digital before the microprocessor can use it — a standalone mark.
The sensor sends to the microprocessor. The microprocessor signals the actuator.
A sensor is an input (captures data); an actuator is an output (performs an action).
Use the exact phrase: compares the reading to a stored value / pre-set value.
Monitoring is continuous — the sensor keeps sending data and the loop repeats.
Check yourself — tap to reveal
Answer in your head, then tap to see the model answer. Aim for 5 of 6 before moving to Learn.
✅ Ready for Learn?
Before moving on, make sure you can answer these without notes:
- Define input device, output device and sensor.
- Why is an ADC needed, and where does it fit?
- What does the microprocessor compare the reading to?
- What is an actuator and what does it do?
- State the full sensor sequence, in order.
Input, Output & Sensors
Input device
Allows data to be entered into a computer system. Data can be text, images, sound, or environmental readings.
Output device
Presents the results of processed data — what you see, hear, or the action taken.
Sensor
A type of input device that captures analogue data from its immediate environment at set time intervals.
Input devices you must know
| Device | Data type | Example use |
|---|---|---|
| Keyboard | Text / numbers | Typing documents, entering data |
| Optical mouse | Position / movement | Navigating, selecting on screen |
| Microphone | Sound / audio | Voice recording, video calls |
| Digital camera | Images / video | Photography, video conferencing |
| Scanner (2D/3D) | Images / 3D models | Digitising documents, 3D modelling |
| Barcode scanner | Barcode data | Supermarket checkout, stock control |
| QR code scanner | QR code data | Website links, ticket scanning |
| Touch screen | Position / gesture | Phones, tablets, ATMs |
Output devices you must know
| Device | Output type | Example use |
|---|---|---|
| Monitor/screen (LCD/LED) | Visual display | Viewing documents, videos |
| Inkjet printer | Printed paper | Home printing, photos |
| Laser printer | Printed paper | Office, high-volume printing |
| 3D printer | Physical 3D object | Prototyping, manufacturing |
| Speaker | Sound / audio | Music, alerts, voice output |
| Projector (DLP/LCD) | Projected image | Presentations, cinema |
| Actuator | Physical movement/action | Automated systems, robotics |
Sensors
| Sensor | Measures | Example use |
|---|---|---|
| Temperature | Heat level | Air conditioning, greenhouse |
| Light | Light level | Automatic streetlights |
| Pressure | Force/weight | Automatic doors, car seats |
| Gas | Gas concentration | Carbon monoxide detector |
| Humidity | Moisture level | Greenhouse, art gallery |
| Infra-red | IR radiation / heat | Security systems, intruder detection |
| Acoustic | Sound level | Security (window break), noise monitoring |
| Accelerometer | Movement / vibration | Phone screen rotation, car airbags |
| Flow | Liquid/gas flow rate | Factory pipes, nuclear plants |
| Level | Liquid level | Water tank, reservoir monitoring |
| Moisture | Soil/surface moisture | Automatic garden irrigation |
| Proximity | Distance to object | Robots, parking sensors |
| pH | Acidity/alkalinity | Water treatment, swimming pools |
How sensors work in automated systems
1. Sensor captures analogue data from the environment at set intervals.
2. Data is sent to the microprocessor for processing.
3. Data is compared against stored/preset values.
4. If the reading is outside the range, the system takes action (via actuator or other output).
5. System operates without human intervention.
Quick check
A sensor captures:
Activity 1 — Input, Output or Sensor?
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Activity 2 — Match the Sensor
Which sensor is needed for this scenario?
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Activity 3 — Spot the Mistake
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Adaptive practice
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Cambridge-style questions
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Review quiz
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Exam traps
Memory triggers
🧠 "Input = IN, Output = OUT"
Input puts data IN. Output gets results OUT. Simple.
🧠 "Sensor = sense the environment"
Sensors sense things around them — temperature, light, pressure, gas.
🧠 "Actuator = acts physically"
An actuator ACTS — it moves, opens, closes, switches something on/off.