# 3.2 Input & Output Devices

## Input Devices

Input devices convert real-world inputs into digital data which can be processed by a microprocessor.

### Barcode Scanner

* Shines a red laser at the barcode to read the data
* The light from the white lines is reflected back but black lines absorb the light
* The <mark style="color:yellow;">different levels of reflection are converted into a binary value</mark>
* Used for identifying or tracking a product
* Some benefits include, faster checkouts, automated stock control, less chance of error, more detailed tracking information

{% hint style="success" %}
Sample answer:

Device shines a laser at the barcode\
The white areas reflect the light while the black absorbs light\
The device reads the reflected light using sensors\
The reflected light is converted into binary
{% endhint %}

### Digital Camera

* Works by capturing light and converting it into a digital image
* Light enters through the lens and reaches the image sensor
* Each <mark style="color:yellow;">pixel measures light intensity which is converted into binary</mark>
* Some benefits include, you see a preview of the image, the image can instantly be duplicated, and software can be used to edit digital photos

### Keyboard

* Text-based data input
* Each key has a peg underneath which makes contact with a conducting membrane
* This is <mark style="color:yellow;">converted into an electrical signal to transmit a unique character code</mark>

{% hint style="success" %}
Sample answer:

Membrane with circuit board present at the base of the keys\
When a key is pressed, this presses a switch\
This completes a circuit\
The location of the keypress is calculated\
An index of characters is searched to find which key was pressed\
Each character has a Unicode value which is then converted into binary\
This is then processed by the CPU to action the keypress
{% endhint %}

### Microphone

* Converts sound waves into electrical signals
* Capture real world sound and convert it into digital data using an ADC[^1] \*
* Has a diaphragm that vibrates in response to sound waves
* Vibrations are <mark style="color:yellow;">converted into electrical signals by a coil of wire</mark> attached to the back of the diaphragm

\* Analogue data is non-discrete and digital data is discrete, so non-discrete data is being converted into discrete data. <mark style="color:purple;">(Note: this may come up as an exam question)</mark>

### Optical Mouse

* Uses a laser to detect and track movement (replicates on-screen)
* Used to control the cursor in GUIs
* Reliable due to no moving parts

### QR Code Scanner

* A QR code is a visual representation of data using black and white squares
* Can represent over 7000 digits (barcode is 30)
* Scanned by a camera
* Software <mark style="color:yellow;">converts the squares into binary</mark>

{% hint style="success" %}
Sample answer:

Device shines a laser at the QR code\
The corners are used to determine position or orientation\
The white areas reflect the light while the black absorbs light\
The device reads the reflected light using sensors\
The reflected light is converted into binary\
A link or URL is stored within the QR code
{% endhint %}

### Touchscreen

#### Resistive screen

These consist of two conductive layers. The top layer is flexible. When the screen is touches, the two layers connect, completing a circuit.

#### Infra-red screen

LEDs shine infrared light across a screen forming a matrix. When the screen is touches, the beams are interrupted.

#### Capacitive screen

These are made up of a protective layer, a transparent conductive layer, and a glass substrate. Touching the screen changes the electrostatic field of the conductive layer.

<table><thead><tr><th width="128">Type</th><th width="196">Usecases</th><th>Benefits / Drawbacks</th></tr></thead><tbody><tr><td>Resistive</td><td>Cash machines<br>Medical equipment<br>Information kiosk</td><td>Cheap to produce<br>Resistant to surface contaminants<br>Can be activated with every object</td></tr><tr><td>Infra-red</td><td>Tablets<br>Laptops<br>Phones</td><td>Excellent image quality<br>High precision and durable<br>Allows for multiple touches at the same time<br>Requires a bare finger or stylus for activation</td></tr><tr><td>Capacitive</td><td>Commercial displays<br>Medial equipment<br>Information kiosk</td><td>Excellent image quality<br>Unlimited touch-life<br>Scale well<br>Sensitive to interference (light, water, snow)</td></tr></tbody></table>

### 2D & 3D Scanners

* 2D  ->  flatbed shines a strip of light over a document, <mark style="color:yellow;">reflected light is measured for each pixel</mark>, data is converted into binary so document can be digitally recreated.
* Some uses are scanning documents or reading passports<br>
* 3D  ->  shines a light over an object, geometry and dimensions are recorded so object can be recreated digitally.
* 3D model can be modified using software
* Can be used to create 3D models with CAD
* Some uses are dentistry, product development&#x20;

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## Output Devices

A device shows the results of the processing in a way humans can understand (using a screen).

### Actuators

* Used with a motor to translate energy into real-world movement of a physical object
* Often used with sensors, the <mark style="color:yellow;">input of the sensor is checked against stored values</mark>

### Light Projectors

* Project computer outputs onto a large screen
* DLP (<mark style="color:yellow;">Digital Light Processing</mark>) projectors use millions of micromirrors arranged in a grid. Light is shone through the colour filters and mirrors. The position of the mirrors can be altered to change the intensity of the light.
* LCD (<mark style="color:yellow;">Liquid Crystal Display</mark>) projectors use three mirror filters to separate an image in to RGB wavelengths. The three images are then combined to produce the full colour image.

<table><thead><tr><th width="84">Type</th><th>Advantages</th><th>Disadvantages</th></tr></thead><tbody><tr><td>DLP</td><td>Higher contrast ratios<br>Smooth video<br>Higher reliability<br>Smaller &#x26; lighter<br>Better suited to dusty atmospheres</td><td>Image suffers from shadows<br>No grey components in the image<br>Colour definition is not as good as LCD</td></tr><tr><td>LCD</td><td>Sharper image<br>Better colour saturation &#x26; intensity<br>Use less power, less heat<br>Quieter to run</td><td>Contrast ratios not as good as DLP<br>Have a limited life<br>Panels degrade over time</td></tr></tbody></table>

### Laser & Inkjet Printers

Both types create hard copies of a digital document.

#### Laser Printers

* Very fast when making multiple copies
* Useful for high volume print jobs
* Have a low running cost per page
* Often used in business or education
* Have large toner (dry ink) and large paper trays
* Use positive & negative charges to make the toner particles stick to the paper, heat is used to bond the particles to the paper

#### Inkjet Printers

* A print head moves across the page
* Spray liquid ink droplets from ink cartridges onto the paper
* Droplets can be piezoelectric or thermal bubble technology
* Produce high quality hard copies

### 3D Printers

* Create 3D models by depositing material on top on one another (plastic or resin)
* Allows for precision (used in medicine to create prosthetics)
* Can be used to create rapid prototypes
* Models can be transmitted digitally and then printed

### LCD Screens

* Millions of tiny liquid crystals
* Made of pixels arranged in a matrix
* Display requires backlighting
* Used for TVs, monitors, phones
* Low power consumption, no heat
* Do not suffer from image burn or flicker issues
* Provide bright images and colours
* Cheap to produce than LED screens

### LED Screens

* Made of tiny LEDs
* Do not need backlighting (thinner and lighter)
* Better image quality and longer life
* Can be used to create very large screens
* Consume very little power

{% hint style="success" %}
Sample answer:

Display is made up of different pixels that are arranged in a matrix\
LEDs are behind the screen\
Light is shone at the pixels through a diffuser to distribute the light evenly\
RGB filters are used and mixed to create different colours
{% endhint %}

### OLED Screens

* Much thinner and lighter than LCD screens
* Use Organic Light Emitting Diodes
* Use organic carbon compound to create semi-conductors
* Very thin, flexible screens

### Speakers

* Used for digital sounds or recordings and output them as sound waves
* Digital data is changed into an electric current (ADC)
* Passed through an amplifier to create a large current
* Loudspeaker converts current into a sound wave

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## Sensors

These measure a physical property of their environment. They can be used to monitoring and control systems.

<table><thead><tr><th width="156">Type</th><th width="235">Variable</th><th>Usecase</th></tr></thead><tbody><tr><td>Acoustic</td><td>Sound</td><td>Detect sound changes in machinery<br>Monitor noise pollution<br>Security system</td></tr><tr><td>Accelerometer</td><td>Acceleration<br>Tilt<br>Vibration</td><td>Sudden changes in vehicle movement<br>Detect orientation of device</td></tr><tr><td>Flow</td><td>Rate of gas / liquid flow</td><td>Detect changes in water flow of pipes</td></tr><tr><td>Gas</td><td>Presence of a gas</td><td>Levels of gas in confined spaces<br>When fixing gas leaks</td></tr><tr><td>Humidity</td><td>Water vapour</td><td>Greenhouses</td></tr><tr><td>Infra-red</td><td>Motion<br>Heat source</td><td>Security systems detect intruders<br>Emergency services to detect people</td></tr><tr><td>Level</td><td>Liquid</td><td>Petrol in a car<br>Water in a tank</td></tr><tr><td>Light</td><td>Light</td><td>Headlights</td></tr><tr><td>Magnetic field</td><td>Presence &#x26; strength</td><td>Anti-lock braking system</td></tr><tr><td>Moisture</td><td>Moisture</td><td>Soil and buildings</td></tr><tr><td>pH</td><td>Acidity<br>Alkaline</td><td>Soil<br>Chemical processes</td></tr><tr><td>Pressure</td><td>Gas / liquid</td><td>Tyre pressure<br>Pipes</td></tr><tr><td>Proximity</td><td>Distance</td><td>Robotics<br>Safety systems</td></tr><tr><td>Temperature</td><td>Temperature</td><td>Swimming pools<br>Chemical processes</td></tr></tbody></table>

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## Exam Questions

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[^1]: Analogue to Digital Converter