← IGCSE Computer Science Paper 1

Comparing resistive, capacitive and infra-red touch screens

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.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 14

Understanding Comparing resistive, capacitive and infra-red touch screens in IGCSE Computer Science Paper 1

What it does: Infra-red screens sense a broken light beam, so they suit large displays such as information kiosks. Resistive screens sense pressure: pressing makes the top layer touch the layer below, which changes the electrical signal. Capacitive screens detect the small change in electric charge that a conductive finger causes on the screen. Resistive screens use simple layers, so they cost less. Capacitive screens cost more but give a clearer, more responsive display.

Common mistakes: A resistive screen works by pressing layers together, so a stylus, a gloved finger or a bare finger all work. Only a capacitive screen needs a bare finger. A capacitive screen detects the electric charge of a finger. Sensing pressure on layers is how a resistive screen works.

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This module's key terms are also in a printable crossword (Modules 252–261) and word search (Modules 240–261).

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Learning
Duo
Which touch screen type detects touch when two conductive layers are pressed together?
CapacitiveResistive
Matches
Capacitive screens work with any object, like a glove
↓
Capacitive screens need the electric charge of a bare finger, so gloves do not work. Resistive screens work with gloves because they sense pressure.
Applying
Meanings
Term
resistive, capacitive, infra-red
Meaning
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.
Practice
screen ← "capacitive"
Testing
Gaps
OUTPUT + " senses pressure"
Check Answer
Spots
2detects = "pressure"
3touch_with = "bare finger only"

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Quick Questions

1. Which touch screen type detects touch when two conductive layers are pressed together?
A. Capacitive
B. Resistive ✓
Resistive screens sense pressure: pressing makes the top layer touch the layer below, which changes the electrical signal.
2. Which touch screen type senses the electric charge of a finger?
A. Capacitive ✓
B. Infra-red
Capacitive screens detect the small change in electric charge that a conductive finger causes on the screen.
3. Which touch screen type detects touch when a grid of light beams is broken?
A. Resistive
B. Infra-red ✓
Infra-red screens have beams across the surface. Anything that blocks a beam shows where the touch happened.
4. A user wearing thick gloves wants to use a touch screen on a factory machine. Which type works best?
A. Resistive, because pressure from any object works ✓
B. Capacitive, because gloves carry electric charge
Resistive screens respond to pressure from gloves or a stylus. Capacitive screens need a conductive touch such as a bare finger.
5. Which statement about multi-touch (pinch to zoom) is most accurate for a modern smartphone?
A. Capacitive screens handle multi-touch very well ✓
B. Resistive screens handle multi-touch best
Capacitive screens are good at multi-touch, which is why smartphones use them. Resistive screens usually cope poorly with it.

Match the Pairs

Resistive: top layer pressed onto bottom layer → Touch is detected by pressure pushing two layers together, so a gloved finger or stylus works
Capacitive: finger changes electric charge → Touch is detected from the charge of a bare finger, so gloves and plastic styluses do not work and multi-touch is easy
A screen that detects a broken beam of light is best for a large public display → Infra-red: beams across the screen
A phone needs a clear, multi-touch screen that is sensitive to a bare finger → Capacitive: smartphone screen
Capacitive screens work with any object, like a glove → Capacitive screens need the electric charge of a bare finger, so gloves do not work. Resistive screens work with gloves because they sense pressure.
Resistive screens are the clearest and detect touch using electric charge → Resistive screens detect touch by pressure on layers, and their extra layers make the picture less clear than capacitive screens.

Key Term

resistive, 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.

Fill in the Blanks

1. OUTPUT resistive + " senses pressure"
Hint: Type the touch screen type that detects pressure pressing layers together.
2. IF object = finger THEN works ← TRUE
Hint: Type the thing that a capacitive screen senses through its electric charge.
3. IF beam = "broken" THEN touch ← "infra-red" ENDIF
Hint: Type the pseudocode keyword that starts the action when the IF condition is met.
4. IF screen = "resistive" THEN OUTPUT "pressure" ENDIF
Hint: Type the pseudocode keyword that displays a value on screen.
5. device ← "phone" screen ← "capacitive"
Hint: Type the touch screen type that suits a smartphone because it senses a finger's charge and allows multi-touch.

Spot the Error

Question 1
A screen = "resistive"
B detects = "pressure"
C touch_with = "bare finger only"
D multi_touch = False
Line C — A resistive screen works by pressing layers together, so a stylus, a gloved finger or a bare finger all work. Only a capacitive screen needs a bare finger.
Question 2
A screen = "capacitive"
B detects = "pressure on layers"
C multi_touch = True
Line B — A capacitive screen detects the electric charge of a finger. Sensing pressure on layers is how a resistive screen works.
Question 3
A screen = "infra-red"
B detects = "electric charge"
C cost = "high"
Line B — An infra-red screen detects a touch when an object breaks a grid of infra-red light beams. Sensing electric charge is capacitive.
Question 4
A needs_stylus = True
B if needs_stylus:
C choice = "capacitive"
D print(choice)
Line C — A stylus does not carry the electric charge a capacitive screen needs. A resistive screen works with a stylus because it senses pressure.
Question 5
A device = "phone"
B if device == "phone":
C screen = "capacitive"
D multi_touch = False
E print(screen)
Line D — Capacitive screens support multi-touch, such as pinch to zoom on a phone. The line should be multi_touch = True.

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