← IGCSE Computer Science Paper 1

Analogue sensor data and analogue-to-digital conversion

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

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 33, IGCSE Computer Science 0478 — 6.1 Automated Systems — Module 3, ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data — Module 27, QCE Digital Solutions Unit 3 — Interactions Between Users, Data and Digital Systems — Module 77

Understanding Analogue sensor data and analogue-to-digital conversion in IGCSE Computer Science Paper 1

What it does: A smooth, continuously varying value with many decimal places is typical of analogue data from a sensor. Physical quantities like temperature, light and pressure change smoothly, so sensors capture analogue data. The ADC turns analogue readings into digital values. A DAC does the opposite job. The ADC comes before processing, because the microprocessor can only work with digital values. Sensors take readings at regular intervals so the computer always has up-to-date data. After the ADC, the reading is a digital binary number the computer can store and process. An ADC sits between the sensor and the processor, converting analogue input into binary numbers.

Common mistakes: The raw sensor reading is analogue, and a computer cannot process it directly. The ADC output must be processed instead: PROCESS(digital). A DAC turns digital values into analogue. Sensor readings are analogue, so they need an ADC: digital ← ADC(raw).

Class: _____________________  ·  Name: _____________________  ·  Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

🖨 Print worksheet + answer key Add Analogue sensor data and analogue-to-digital conversion to a class →

This module's key terms are also in a printable crossword (Modules 273–282) and word search (Modules 262–282).

Take this worksheet further — free with Cloodit

Each concept is reinforced from every angle — learned, then applied, then tested.

Learning
Duo
A temperature sensor measures a room warming up gradually. What type of data does it capture?
Analogue data, which varies continuouslyDigital data, which is already in binary
Matches
sensor -> microprocessor -> ADC
↓
The ADC is placed after the microprocessor. It must come before processing, because the computer can only process digital data and the sensor gives analogue data.
Applying
Meanings
Term
ADC (analogue-to-digital converter)
Meaning
Turns the continuously varying analogue readings from a sensor into digital values (binary numbers) so a computer can process them.
Practice
WHILE TRUE
Testing
Gaps
digital ← (temperature)
Check Answer
Spots
3 digital ← ADC(raw)
4 PROCESS(raw)

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

The 'Barreleye Fish' badge — Clear Vision, one of Cloodit's 106 collectible badges
Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy
Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games
Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print
Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Add to class →

Quick Questions

1. A temperature sensor measures a room warming up gradually. What type of data does it capture?
A. Analogue data, which varies continuously ✓
B. Digital data, which is already in binary
Physical quantities like temperature, light and pressure change smoothly, so sensors capture analogue data.
2. Which device must change a sensor's reading before a computer can process it?
A. Digital-to-analogue converter (DAC)
B. Analogue-to-digital converter (ADC) ✓
The ADC turns analogue readings into digital values. A DAC does the opposite job.
3. A computer works with data in which form?
A. Digital values (binary numbers) ✓
B. Continuously varying analogue signals
Computers process binary data, which is why analogue sensor data has to be converted first.
4. A light sensor sends its reading to a microprocessor. Where does the ADC sit in this process?
A. Between the sensor and the microprocessor ✓
B. After the microprocessor has processed the data
The ADC comes before processing, because the microprocessor can only work with digital values.
5. Which statement about analogue data is correct?
A. It can only take fixed steps such as 0 or 1
B. It can take any value within a range, such as 20.1, 20.15 or 20.2 ✓
Analogue means continuously varying. Fixed separate values are a feature of digital data.

Match the Pairs

ADC → Analogue-to-digital converter: changes the continuously varying readings from a sensor into digital values the computer can process
DAC → Digital-to-analogue converter: changes digital values from the computer into an analogue signal, for example to drive a speaker or motor
Analogue data varies continuously, so a temperature sensor can output any value in a range such as 21.3, 21.4 or 21.45 → temperature = 21.37
The sensor's reading must be converted by the ADC before the microprocessor can process it → sensor -> ADC -> microprocessor
sensor -> microprocessor -> ADC → The ADC is placed after the microprocessor. It must come before processing, because the computer can only process digital data and the sensor gives analogue data.
A light sensor sends digital values straight to the computer, so no ADC is needed → Sensors capture analogue data, not digital data. An ADC is needed to convert the readings into digital values before the computer can use them.

Key Term

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

Fill in the Blanks

1. digital ← ADC(temperature)
Hint: Type the abbreviation for the converter that changes a sensor's analogue reading into a digital value.
2. digital ← ADC(ReadSensor()) IF digital > 200 THEN OUTPUT "Too hot"
Hint: Type the keyword that lets the computer process the digital value and make a decision.
3. signal ← DAC(digital_value)
Hint: Type the abbreviation for the converter that turns a digital value back into an analogue signal for an output such as a speaker.
4. WHILE monitoring = TRUE digital ← ADC(ReadSensor()) ENDWHILE
Hint: Type the loop keyword that makes the sensor readings be taken again and again at regular intervals.
5. analogue ← ReadSensor() digital ← ADC(analogue)
Hint: Type the variable that holds the raw, continuously varying reading to be converted.

Spot the Error

Question 1
A REPEAT
B raw ← READ_SENSOR()
C digital ← ADC(raw)
D PROCESS(raw)
E UNTIL SwitchOff = TRUE
Line D — The raw sensor reading is analogue, and a computer cannot process it directly. The ADC output must be processed instead: PROCESS(digital).
Question 2
A REPEAT
B raw ← READ_SENSOR()
C digital ← DAC(raw)
D WAIT 10 SECONDS
E UNTIL done = TRUE
Line C — A DAC turns digital values into analogue. Sensor readings are analogue, so they need an ADC: digital ← ADC(raw).
Question 3
A digital ← 128
B signal ← ADC(digital)
C OUTPUT signal TO SPEAKER
Line B — A speaker needs an analogue signal, so the digital value must go through a DAC (digital-to-analogue converter), not an ADC: DAC(digital).
Question 4
A reading ← READ_SENSOR()
B // ADC gives binary values
C // ADC gives binary values
Line C — This line is fine as a comment, so the error is elsewhere in the program.
Question 5
A WHILE monitoring = FALSE
B raw ← READ_SENSOR()
C digital ← ADC(raw)
D WAIT 1 SECOND
E ENDWHILE
Line A — The loop must run while monitoring is TRUE, so readings are taken at regular intervals. With FALSE it never runs while monitoring is on.

Student with a class code? Join your class →