← IGCSE Computer Science Paper 1

Accelerometer sensor

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

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 35, IGCSE Computer Science 0478 — 6.1 Automated Systems — Module 22, ACARA Digital Technologies Years 7–8 — Acquiring and Storing Data — Module 18

Understanding Accelerometer sensor in IGCSE Computer Science Paper 1

What it does: Each step causes a small movement that the accelerometer senses, so the microprocessor adds one to the step count. The accelerometer detects the tilt of the phone so the screen can switch between portrait and landscape. Brightness is controlled by a light sensor. A sudden large change in speed shows a crash, so the microprocessor can trigger the airbag. Fuel level is measured by a level sensor. Accelerometers can detect the angle a device is held at, which is how a phone knows it has been turned on its side. Acceleration is how quickly speed or direction changes, not the distance travelled.

Common mistakes: When the accelerometer detects the phone tilted sideways, the screen should rotate to landscape, not stay in portrait. Each jolt from a footstep, detected by the accelerometer, should add 1 to the step count. It should be steps <- steps + 1.

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Learning
Duo
Which data does an accelerometer capture?
The amount of light falling on itAcceleration (change in speed or direction) and tilt
Matches
A phone uses an accelerometer to measure the temperature of its battery
↓
An accelerometer does not measure temperature. It measures acceleration, movement and tilt. A temperature sensor measures heat.
Applying
Meanings
Term
accelerometer
Meaning
A sensor that measures acceleration (change in speed or direction) and tilt. Used for phone screen rotation, step counters and car airbag impact detection.
Practice
force ← accelerometer_reading
Testing
Gaps
tilt ← READ()
Check Answer
Spots
2IF tilt = sideways THEN
3 rotate screen to portrait

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Quick Questions

1. Which data does an accelerometer capture?
A. Acceleration (change in speed or direction) and tilt ✓
B. The amount of light falling on it
An accelerometer measures movement, tilt and impact. A light sensor is the one that measures brightness.
2. Which device feature uses an accelerometer to turn the screen when you rotate the phone?
A. Phone screen rotation ✓
B. Phone screen brightness
The accelerometer detects the tilt of the phone so the screen can switch between portrait and landscape. Brightness is controlled by a light sensor.
3. A step counter detects each step by sensing...
A. The temperature of the person's skin
B. The movement of the body as each step is taken ✓
Each step causes a small change in acceleration, which the accelerometer picks up and the counter adds up.
4. In a car, what does an accelerometer help an airbag system to detect?
A. A sudden impact or sharp slowing down ✓
B. The level of fuel in the tank
A sudden large change in speed shows a crash, so the microprocessor can trigger the airbag. Fuel level is measured by a level sensor.
5. True or false: an accelerometer can measure the tilt of a device.
A. False
B. True ✓
Accelerometers can detect the angle a device is held at, which is how a phone knows it has been turned on its side.

Match the Pairs

accelerometer → A sensor that measures acceleration (change in speed or direction) and the tilt of a device
accelerometer reading changes when phone is turned sideways → The sensor detects the tilt of the device, so the screen can rotate
A step counter uses an accelerometer to detect the repeated movement of walking → IF accelerometer detects a jolt THEN steps ← steps + 1
A car airbag system uses an accelerometer to detect a sudden impact → IF acceleration < -50 THEN inflate airbag
A phone uses an accelerometer to measure the temperature of its battery → An accelerometer does not measure temperature. It measures acceleration, movement and tilt. A temperature sensor measures heat.
An accelerometer only measures when a device is moving at a constant speed → An accelerometer measures acceleration, which is a change in speed or direction, so a constant speed gives no acceleration.

Key Term

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

Fill in the Blanks

1. tilt ← READ(accelerometer) IF tilt > 45 THEN ENDIF
Hint: Type the name of the sensor that measures acceleration and the tilt of a device.
2. IF tilt > 45 THEN OUTPUT "Landscape" ENDIF
Hint: Type the keyword that starts a condition, so the screen rotates only when the tilt is large enough.
3. IF impact > 8 THEN OUTPUT "Inflate airbag" ENDIF
Hint: Type the comparison operator for 'greater than', so the airbag fires when the impact is too big.
4. IF movement = TRUE THEN steps ← steps + 1 ENDIF
Hint: Type the arithmetic operator that adds one to the step counter each time movement is detected.
5. IF impact > 8 THEN OUTPUT "Inflate airbag" ENDIF
Hint: Type the keyword that closes the selection block that started with IF.

Spot the Error

Question 1
A tilt <- accelerometer.read()
B IF tilt = sideways THEN
C rotate screen to portrait
D ENDIF
Line C — When the accelerometer detects the phone tilted sideways, the screen should rotate to landscape, not stay in portrait.
Question 2
A steps <- 0
B IF jolt detected THEN
C steps <- steps - 1
D OUTPUT steps
Line C — Each jolt from a footstep, detected by the accelerometer, should add 1 to the step count. It should be steps <- steps + 1.
Question 3
A impact <- accelerometer.read()
B IF impact < 50 THEN
C inflate airbag
D ENDIF
Line B — The airbag must inflate only when the accelerometer reads a very large, sudden change in speed. The condition should be impact > 50.
Question 4
A tilt <- microphone.read()
B IF tilt > 45 THEN
C rotate screen
D ENDIF
Line A — A microphone captures sound, not tilt. Tilt is measured by an accelerometer, so it should be tilt <- accelerometer.read().
Question 5
A steps <- 0
B WHILE app is open
C IF jolt detected THEN
D steps <- steps * 2
E ENDIF
F ENDWHILE
Line D — A step counter adds 1 for each movement the accelerometer detects. Multiplying by 2 would give a wrong count. It should be steps <- steps + 1.

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