# GCSE Computing/Computing hardware/Input and output devices

Input Device - Devices that send data or instructions into a computer

Device Description Image
Mouse Used for screen input
mouse
Keyboard

The keyboard is one of the most popular ways of inputting information into a computer. The basic mechanical keyboard relies on springed keys being pressed down to complete an electrical circuit. This circuit then transmits a binary signal (commonly using ASCII) to the computer to represent the key pressed.

Stylised cross-section of a Chiclet keyboard (there are other technologies out there used to make keyboards). The bottom right hand button has been pressed, completing the circuit shown in red.

There are many different keyboard layouts, with differences between languages and countries. The most popular layout is the QWERTY keyboard. Other layouts include:

• AZERTY - for countries such as France and Belgium
• QWERTZ - for countries such as Germany and Austria
• Arabic - different values to most keys
• Ukranian
• Chinese - laid over a QWERTY keyboard

There are variations QWERTY keyboard with the UK and the USA having very slight differences in layout. There also variations in English language keyboards such as the Dvorak layout, which followers claim to be superior to QWERTY.

QWERTY keyboard
Voice recognition Microphone connected to software that converts human speech into commands or text.

Pros

Natural interface with a computer allowing for new users to execute commands without having to learn complex command set

Cons

Speech recognition might not recognise the difference between similar words i.e. "their" and "they're" or be able to understand regional accents
microphone
Digital camera
1. Light is focused through the lens onto the image sensor at the back of the camera
2. The image sensor is made up of an array of Red, Green and Blue photosensors, called a Bayer filter. Each sensor will only record values for that particular colour.

And became these:

1. The different colour arrays are combined to form an image and makes this:

Once the RGB values have been captured, they can then be stored digitally using SD or compact flash cards. Save formats include JPEG or TIFF.

Pros

• You can preview images taken without having to get them developed
• You can apply filters and images to add special effects

Cons

• Some people argue that the quality of photos taken using the traditional film medium is better
Camara2sig
Barcode reader Used in supermarkets, keeping track of produce etc. They allow for quick reading of product details so that prices and information can be retrieved and/or stock levels updated. However the amount of data stored in a barcode is very limited
barcodes are very common
1. A laser is directed towards the barcode, scanning across it and the reflected light is captured by the reader
2. The intensity of light reflected back is read by a sensor in the bar code reader
1. High intensity = white bar
2. Low intensity = black bar
3. The pattern received is translated into a code which gives the identity of the barcode being scanned
4. This code is checked against a product database and the product details displayed
Plessey code is one way to encode barcodes

To make sure that the number you have received is correct barcodes employ check digits. Read on to find out more

Pros

Cheap to produce as all you need to do is print a black and white image
Quick to read, and with multi-direction scanners, can be read from different angles

Cons

Only a limited amount of data can be stored
Optical mark reader Used in things like multi choice question papers. The student would be given a selection of answers and then mark the ones they thought correct with a pen or pencil. When finished, the forms would be fed into a machine that would look for black marks. The position of these marks correspond to answers and the form could be marked at some speed.
multi choice exam paper ready for OMR
Optical character reader Used in scanning printed or written text into a digital format. Recently used by Amazon and Google to scan books.
Sketch of a typical manual book scanner
Magnetic stripe reader Used to read data from bank cards and access cards. Data is stored in the magnetic, generally black, strip on the back of these cards
An example of the reverse side of a typical credit card: Green circle #1 labels the Magnetic stripe
Smart card reader Used in bank cards, often known as part of 'chip and pin'. More secure than Magnetic stripes though more expensive to produce.
RFID reader Used to read data without physical contact. Examples include the London Oyster Card System. Where the card has a Radio Frequency Identification(RFID) chip.
1. The card is the placed above a reader and the magnetic field produced by the reader induces a current in the cards circuitry (no physical contact is required)
3. If the details of the card are legitimate then it lets the person through the gate

Pros

Can be read without physical contact (health and safety concerns)
Fast way to pay for things

Cons

Having multiple RFID cards together, means that they can interfere with each other and none of them can be read

A damaged card, revealing the microchip in the lower right corner, and the aerial running around the edge of the card.
Oyster card readers on London Underground ticket barriers at Canary Wharf.

## Touch sensitive

More and more devices are relying on touch technologies.

Device Description Image
Touch-sensitive screen
1. Each of the four corners of a screen emits a uniform electric field which covers the screen
2. When you place your finger on or near the screen it disrupts this field and draws current
3. measuring the amount of current pulled from each corner you can triangulate the position of the finger

Pros

Natural, intuitive interface with devices
The ability to remap screen functions to suit the task (for example bringing up a keyboard when necessary

Cons

Cold weather can effect the functioning of touch screens
Won't work through gloves, as this stops your fingers conducting electricity

Graphics tablet Used in the design and architectural industries. This allows for people to draw on the tablet in a natural way (as they would with a pencil and paper) and for their drawing to appear on the computer.
Wacom Pen-tablet

## Scanners

Several of the scanners featured here record biological (bio) measurements (metrics) about human beings. Physical data such as finger prints are unique to each person.

Device Description Image
Flatbed Scanner Flat bed scanners are used to convert images and text into a digital format.
The main components of a flatbed scanner
1. Place the object you want to scan on the glass pane, face down
2. the light moves to the start of the document and illuminates a slice
3. The slice is reflected into the CCD where it's image is stored
4. the light and mirror move down to the next slice and so on
5. once all the slices are completed the image is assembled using them into a digital image
Flatbed Scanner
Fingerprint Scanner
A finger print
The ridges and troughs on a person's finger and toes are unique to that person. Using a scanner a finger print pattern can be recorded and compared to others on a database, allowing a computer to match finger prints from crimes to a suspect, or to allow people into restricted areas.
Fingerprint scanner in Tel Aviv
Retina Scanner
The blood vessels in a normal human retina form a unique pattern for each person

Retina scanners are used to record the pattern of blood vessels at the back of someone's eye. As every has a different pattern of vessels, then retina scanners can be used to uniquely identify people and are very difficult to fake.

...
Iris Scanner
Iris patterns can be different colours and form a unique identifier for each person

By taking a picture of the blood vessels and colouring of someone's eye, we can get a unique pattern that can be used to identify individuals. People might try and circumvent this by using contact lenses

A U.S. Marine Corps Sergeant uses an iris scanner to positively identify a member of the Baghdadi city council prior to a meeting with local tribal leaders, sheiks, community leaders and U.S. service members.
 Exercise: Scanners Explain how a flat bed scanner works Answer: Place the object you want to scan on the glass plane, face down the light moves to the start of the document and illuminates a slice The slice is reflected into the CCD where it's image is stored the light and mirror move down to the next slice and so on once all the slices are completed the image is assembled using them Give two examples of devices that collect biometric data Answer: Retina scanners Finger print scanners Iris recognition

## Check digits

Check Digit - an additional digit added to a data string and depending on that string, used for checking that the string has been sent correctly

With input devices we have a lot of data being sent into the computer, with image capture devices we could be talking about billions of ones and zeroes. How can we make sure that they all get from the input device to the computer safely, without becoming corrupted? There are many error checking methods out there and you will cover some of them in more detail in Unit 1, however, for the moment we will learn a little about check digits:

An example of using check digits (The exam will not expect you to know this technique) is the final digit of a Universal Product Code computed as follows:

1. Add the digits (up to but not including the check digit) in the odd-numbered positions (first, third, fifth, etc.) together and multiply by three.
2. Add the digits (up to but not including the check digit) in the even-numbered positions (second, fourth, sixth, etc.) to the result.
3. Take the remainder of the result divided by 10 (modulo operation) and subtract this from 10 to derive the check digit.
 Example: Check Digits For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7. Add the odd number digits: 0+6+0+2+1+5 = 14 Multiply the result by 3: 14 × 3 = 42 Add the even number digits: 3+0+0+4+4 = 11 Add the two results together: 42 + 11 = 53 To calculate the check digit, take the remainder of (53 / 10), which is also known as (53 modulo 10), and subtract from 10. Therefore, the check digit value is 7. Correct!
 Exercise: Check digits Calculate the check digit for the following food item "01010101010". Answer: Add the odd number digits: ${\displaystyle 0+0+0+0+0+0=0}$ Multiply the result by 3: ${\displaystyle 0x3=0}$ Add the even number digits: ${\displaystyle 1+1+1+1+1=5}$ Add the two results together: ${\displaystyle 0+5=5}$ To calculate the check digit, take the remainder of (5 / 10), which is also known as (5 modulo 10), and subtract from 10 i.e. (10 - 5 modulo 10) = 5. Therefore, the check digit value is 5. If the remainder is 0, subtracting from 10 would give 10. In that case, use 0 as the check digit. Did the following barcode scan correctly: "01234567890 6". Answer: Add the odd number digits: 0+2+4+6+8+0 = 20 Multiply the result by 3: 20 x 3 = 60 Add the even number digits: 1+3+5+7+9 = 25 Add the two results together: 60 + 25 = 85 To calculate the check digit, take the remainder of (85 / 10), which is also known as (85 modulo 10), and subtract from 10 i.e. (10 - 85 modulo 10) = 5. Therefore, the check digit value is 5. If the remainder is 0, subtracting from 10 would give 10. In that case, use 0 as the check digit. Therefore the check digit given, 6, shows that the code is incorrect. Why do we use check digits? Answer: We use check digits to make sure that data received has been received correctly