Infra-red touch screen

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. How does an infra-red touch screen detect where you touch?

A A touch breaks infra-red beams in a grid across the screen

B A touch changes the electric charge on a glass layer

2. Where are the infra-red emitters and receivers placed?

A Emitters on two sides, receivers on the opposite sides

B Emitters and receivers both on the same side of the screen

3. How is the position of a touch worked out?

A The screen measures how hard the finger presses down

B The broken horizontal and vertical beams give the x and y position

4. Which objects can be used on an infra-red touch screen?

A Any object that breaks the beams, such as a gloved finger or a pen

B Only a bare finger, because it needs to conduct electricity

5. Which use is an infra-red touch screen well suited to?

A A tiny smartwatch screen only

B A large interactive whiteboard or information kiosk

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1infra-red touch screen		AA screen with a grid of infra-red beams across it. A touch breaks beams, and the broken x and y beams give the touch position.
2emitters on two sides, receivers opposite		BThe infra-red LEDs are placed along two edges of the screen. Receivers sit on the opposite edges to detect each beam.
3A touch breaks one beam running across and one beam running down. Together they give the x and y position.		Ctouch_object = finger OR glove OR pen
4It works with any object that blocks the beams, not just a finger, so gloves or a pen can be used.		DWrong: dust or dirt can block the beams and cause false touches, so the screen needs to be kept clean.
5Infra-red screens only work with a bare finger		Ebroken beams: x = 5, y = 3 -> touch at (5, 3)
6Dust on the screen cannot affect an infra-red screen		FWrong: any object that breaks the beams works, such as a gloved hand or a pen. A bare finger is not needed.

Definitions

infra-red touch screen

Fill in the Blanks

Complete each line of code by filling in the missing parts.

An _________ touch screen uses a beam grid

Emitters send beams to _________ opposite

A touch ______ beams in the grid

Broken x and y beams give the touch ________

Dust or dirt can cause a _____ touch

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A emitters ← left AND top sides

B receivers ← left AND top

C beams ← grid of IR light

Question 2

A x_broken ← 6

B y_broken ← 4

C pos ← (x_broken, x_broken)

Question 3

A WHILE screen_on

B scan all IR beams

C IF any beam is broken THEN

D measure finger pressure

E ENDWHILE

Question 4

A object ← glove

B beam_broken ← FALSE

C OUTPUT 'Touch detected'

Question 5

A screen_size ← LARGE

B suits ← phone AND smartwatch

C technology ← infra-red

Answer Key

Infra-red touch screen

Section A: Quick Questions

A — A touch breaks infra-red beams in a grid across the screen

A — Emitters on two sides, receivers on the opposite sides

B — The broken horizontal and vertical beams give the x and y position

A — Any object that breaks the beams, such as a gloved finger or a pen

B — A large interactive whiteboard or information kiosk

Section B: Match the Pairs

infra-red touch screen → A screen with a grid of infra-red beams across it. A touch breaks beams, and the broken x and y beams give the touch position.

emitters on two sides, receivers opposite → The infra-red LEDs are placed along two edges of the screen. Receivers sit on the opposite edges to detect each beam.

A touch breaks one beam running across and one beam running down. Together they give the x and y position. → broken beams: x = 5, y = 3 -> touch at (5, 3)

It works with any object that blocks the beams, not just a finger, so gloves or a pen can be used. → touch_object = finger OR glove OR pen

Infra-red screens only work with a bare finger → Wrong: any object that breaks the beams works, such as a gloved hand or a pen. A bare finger is not needed.

Dust on the screen cannot affect an infra-red screen → Wrong: dust or dirt can block the beams and cause false touches, so the screen needs to be kept clean.

Section C: Definitions

infra-red touch screen — A screen with a grid of infra-red beams across it. A touch breaks beams, and the broken x and y beams give the touch position. Works with any object.

Section D: Fill in the Blanks

An infra-red touch screen uses a beam grid

Emitters send beams to receivers opposite

A touch breaks beams in the grid

Broken x and y beams give the touch position

Dust or dirt can cause a false touch

Section E: Spot the Error

B — The receivers must be on the sides opposite the emitters so the beams cross the screen. They should be on the right and bottom, not the same sides as the emitters.

C — The touch position is the broken x beam and the broken y beam together. The second value should be y_broken, not x_broken again.

D — An infra-red screen does not measure pressure. It works out the position from which x and y beams are broken. The line should find the x and y position.

B — Any object, including a gloved finger, breaks the infra-red beams. So beam_broken should be TRUE and the touch is detected.

B — Infra-red touch screens suit large screens such as kiosks and interactive whiteboards. They are not used on small devices like phones and smartwatches.