← IGCSE Computer Science Paper 1

DLP projector

A projector with a chip of tiny mirrors (one per pixel) that tilt towards or away from the lens to make the image. A spinning colour wheel adds colour.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 23

Understanding DLP projector in IGCSE Computer Science Paper 1

What it does: Each mirror switches between two tilt positions. Light reaches the screen only when the mirror points towards the lens. White light passes through the spinning colour wheel before it hits the mirrors, so the image gets its colours. DLP uses a digital micromirror device (DMD). Liquid crystals are used in LCD projectors, not DLP. The image is formed by the mirrors tilting on and off. The mirrors move, not the lens. DLP projectors display large images in cinemas and presentations. A barcode scanner is an input device, not a projector. DLP stands for digital light processing. The tilting mirrors on the chip are what create the picture.

Common mistakes: A DLP chip has exactly one mirror for each pixel, so it should be mirrorsPerPixel ← 1. A bright pixel needs its mirror tilted towards the lens so light reaches the screen. It should be 'mirror tilts to lens'.

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This module's key terms are also in a printable crossword (Modules 262–272) and word search (Modules 262–282).

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Learning

Duo

What does a DLP projector use to form the image?

A chip covered in thousands of tiny mirrorsA layer of liquid crystals that block light

Matches

DLP projector: uses a layer of liquid crystals to block light for each pixel

↓

This describes an LCD projector. A DLP projector uses tiny tilting mirrors on a DMD chip, not liquid crystals.

Applying

Meanings

Term

DLP projector

Meaning

A projector with a chip of tiny mirrors (one per pixel) that tilt towards or away from the lens to make the image. A spinning colour wheel adds colour.

Practice

FOR EACH pixel ON DLP chip

Testing

Gaps

chip ←

Check Answer

Spots

1chip ← "DMD"

2mirrorsPerPixel ← 100

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Quick Questions

1. What does a DLP projector use to form the image?

A. A chip covered in thousands of tiny mirrors ✓

B. A layer of liquid crystals that block light

DLP uses a digital micromirror device (DMD). Liquid crystals are used in LCD projectors, not DLP.

2. In a DLP projector, how many mirrors on the chip are used for each pixel?

A. One mirror for the whole screen

B. One mirror per pixel ✓

Each tiny mirror on the digital micromirror device represents one pixel of the image.

3. How does a mirror make a pixel look dark in a DLP projector?

A. It tilts away from the lens ✓

B. It tilts towards the lens

A mirror tilted towards the lens reflects light onto the screen (bright pixel). A mirror tilted away sends light elsewhere, so the pixel looks dark.

4. What adds colour to the image in a single-chip DLP projector?

A. A layer of colour filters on a touch screen

B. A spinning colour wheel ✓

The mirrors only reflect light. A spinning colour wheel puts red, green and blue light in front of the mirrors in turn to add colour.

5. Which statement about the DLP chip is correct?

A. The mirrors tilt to reflect light towards or away from the lens ✓

B. The mirrors stay still while the lens moves to make the image

The image is formed by the mirrors tilting on and off. The mirrors move, not the lens.

Match the Pairs

DLP projector → A projector with a chip of tiny mirrors that tilt towards or away from the lens to form the image

Digital micromirror device (DMD) → The chip in a DLP projector that is covered in thousands of tiny mirrors, one for each pixel

A mirror tilted towards the lens makes its pixel bright, and a mirror tilted away makes it dark → mirror = ON (towards lens) or OFF (away from lens)

A spinning colour wheel adds colour to the light so the image is shown in full colour → light -> colour wheel -> mirrors -> lens

DLP projector: uses a layer of liquid crystals to block light for each pixel → This describes an LCD projector. A DLP projector uses tiny tilting mirrors on a DMD chip, not liquid crystals.

DLP projector: one mirror is shared between many pixels on the screen → Each pixel has its own mirror. The DMD has one tiny mirror per pixel, not one mirror shared by many.

Key Term

DLP projector

A projector with a chip of tiny mirrors (one per pixel) that tilt towards or away from the lens to make the image. A spinning colour wheel adds colour.

Fill in the Blanks

1. chip ← DMD

Hint: Type the three-letter abbreviation for the chip covered in tiny mirrors.

2. Number of mirrors per pixel: 1

Hint: Type the number of mirrors that control each pixel.

3. IF mirror is ON THEN light goes to the lens

Hint: Type the part of the projector that the light is reflected towards when a mirror is on.

4. IF mirror tilts away, pixel is dark

Hint: Type the word for the direction a mirror tilts, relative to the lens, to make a dark pixel.

5. colour ← light through spinning colour wheel

Hint: Type the name of the spinning part that adds colour to the image.

Spot the Error

Question 1

A chip ← "DMD"

B mirrorsPerPixel ← 100

C colourSource ← "colour wheel"

Line B — A DLP chip has exactly one mirror for each pixel, so it should be mirrorsPerPixel ← 1.

Question 2

A IF pixel is bright THEN

B mirror tilts away from lens

C ELSE

D mirror tilts away

Line B — A bright pixel needs its mirror tilted towards the lens so light reaches the screen. It should be 'mirror tilts to lens'.

Question 3

A light ← lamp

B wheel ← still colour wheel

C OUTPUT colour image

Line B — The colour wheel must spin so that different colours pass in turn. It should be 'spinning colour wheel'.

Question 4

A FOR each frame

B lamp shines on DMD

C mirrors tilt on or off

D LCD focuses light on screen

E NEXT frame

Line D — The lens focuses the reflected light onto the screen. An LCD is a different type of display technology, so it should be 'lens'.

Question 5

A uses ← []

B APPEND uses, "cinema"

C APPEND uses, "presentation"

D OUTPUT use

Line D — The list is called uses, so the variable name must match. It should be OUTPUT uses.

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