Input devices Cambridge IGCSE Computer Science revision
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In plain words
An input device gets data into a computer. A computer can only work with binary, so every input device has the same basic job: to turn something in the outside world, such as a key press, a sound or light bouncing off paper, into 1s and 0s.
7 things to know
- A barcode scanner shines a red light or laser at the barcode. White bars reflect more light than black bars. A sensor detects the reflected light and it is converted to binary.
- A QR code scanner uses a camera to capture the square pattern. A QR code holds more data than a barcode and can be read by a phone.
- A digital camera uses a lens to focus light on a sensor made of millions of light-sensitive cells. The light at each is converted to a binary value for a pixel.
- A keyboard: pressing a key completes a circuit, and the code for that character is sent to the computer. A microphone turns sound waves into an electrical signal, which is then converted to binary.
- An optical mouse shines a light on the surface under it, and a sensor detects movement by comparing the images it captures.
- Touch screens. Resistive: pressing pushes two layers together to complete a circuit. It works with a gloved finger or a stylus. Capacitive: a finger changes the electrical charge on the glass at that point. It allows multi-touch. Infra-red: a finger breaks a grid of invisible beams across the screen.
- A 2D scanner reflects light off a document to capture a flat image. A 3D scanner uses lasers or patterns of light to capture the shape of a solid object.
Worked example
A supermarket checkout reads the barcode on a tin. Describe how the scanner reads it.
- The scanner shines a red light or laser across the barcode.
- The white bars reflect a lot of light and the black bars reflect very little.
- A sensor in the scanner detects how much light comes back from each part.
- The pattern of reflections is converted to binary, giving the product's code.
Tips and tricks
- Explain how a device works one step at a time: what is shone or pressed, what is detected, and what is converted to binary.
- Know one advantage and one disadvantage of each kind of touch screen. Resistive is cheap and works with gloves but is less sensitive. Capacitive is sharp and allows multi-touch but does not respond to an ordinary glove.
It lands in your notebook with its questions as flashcards.
Input devices: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is the purpose of an input device?
Input goes in, output comes out.
How does a barcode scanner tell the bars apart?
A sensor measures the reflected light.
Which kind of touch screen works by a finger breaking a grid of beams?
The broken beams give the position of the touch.
Which touch screen can be used while wearing ordinary gloves?
It responds to pressure, not to the electrical properties of skin. Of the two, only resistive does.
Which device captures the shape of a solid object?
It can be used to make a model for 3D printing.
What does a microphone do?
The signal is then converted to binary.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
2 questions, 5 marks. Write your answers on paper, then check them.
Input devices
Cambridge IGCSE Computer Science 0478 · 5 marks · papermunch.org
Name ______________________________ Date ______________
Describe how a capacitive touch screen detects a touch.[3]
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The screen has a layer that holds an electrical charge. When a finger touches it, the charge at that point changes. Sensors detect where the change happened, and the position is calculated.
Give two differences between a QR code and a barcode.[2]
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A QR code is a square pattern that stores more data. It can be read by a phone camera, and can hold information such as a web address.
Answers: Input devices
- 1. The screen has a layer that holds an electrical charge. When a finger touches it, the charge at that point changes. Sensors detect where the change happened, and the position is calculated.
- 2. A QR code is a square pattern that stores more data. It can be read by a phone camera, and can hold information such as a web address.