Topic Test 5 - Input and Output Devices

What happens when a barcode is scanned?

• The barcode is first of all read by a red laser or red LED (light emitting diode)

• Light is reflected back off the barcode

• The reflected light is read by sensors

• As the laser or LED light is scanned across the barcode, a pattern is generated, which is converted into digital data (allows the computer to understand).

So the barcode has been read, then what happens?

• The barcode number is looked up in the stock database.

• When the barcode number is found, the stock item record is looked up

• The price and other stock item details are sent back to the checkout.

• the number of stock items in the record is reduced by 1 each time the barcode is read.

• This new value for number of stock is written back to the stock item record.

• The number of stock items is compared to the re-order level; if it is less than or equal to this value, more stock items are automatically ordered.

Describe the advantages of barcodes to the management:

-Easier and faster to change prices on stock items.
-More up-to-date sales information/sales trends.
-No need to price every stock item on the shelves (reduces time and cost to the management).
-Possible to check customer buying habits more easily by linking barcodes to, for example, customer loyalty cards.
-Allows for automatic stock control.

Describe the advantages of barcodes to the customers:

-Faster checkout queues (staff don't need to remember/look up prices of items).
-Better track of 'sell by dates' so food should be fresher.
-Errors in charging customers is reduced.
-Cost savings can be passed on to the customer.
-The customer is given an itemised bill

Name 3 uses of QR codes:

• Advertising products.

• Giving automatic access to a website or contact telephone number.

• Storing boarding passes electronically at airports and train stations.

Describe the purpose of the three large squares at the corners of the QR code:

The three large squares at the corners of the code function as a form of alignment; the remaining small corner square is used to ensure the correct size and correct angle of the camera shot when the QR code is read.

How do you scan a QR code?

• Point the phone or tablet camera at the QR code

• The app will now process the image taken by the camera, converting the squares into readable data.

• The browser software will automatically read the data generated by the app; it will also decode any web addresses contained within the QR code.

• The user will then be sent to a website automatically.

Describe the advantages of using QR codes:

-They can hold much more information.
-There will be fewer errors. (The higher capacity of the QR code allows the use of built-in error-checking systems)
-Easier to read (they don't need LED).
-Easy to transmit QR codes either as text messages or images.
-Possible to encrypt QR codes which gives them greater protection than barcodes.

Describe the disadvantages of using QR codes:

-More than one QR format is available.
-QR codes can be used to transmit malicious codes.

Explain what is meant by 'Attagging':

It is relatively easy to write malicious code and embed this within the QR code. When the code is scanned, it is possible the creator of the malicious code could gain access to everything on the user's phone. The user could also be sent to a fake website or it is even possible for a virus to be downloaded.

Digital cameras are controlled by an embedded system which can automatically carry out the following tasks:

• Adjust the shutter speed.

• Focus the image automatically.

• Operate the flash gun automatically.

• Adjust the aperture size.

• Adjust the size of the image.

• Remove 'red eye' when the flash gun has been used.

What happens when a photograph is taken?

• The image is captured when light passes through the lens onto a light-sensitive cell; this cell is made up of millions of tiny sensors which are acting as photodiodes.

• Each of the sensors are often referred to as pixels.

• The image is converted into tiny electric charges which are then passed through an analogue to digital converter (ADC) to form a digital image array.

• The ADC converts the electric charges from each pixel into levels of brightness.

• The sensors also measure colour which produces another binary pattern.

• The number of pixels determines the size of the file used to store the photograph.

• The quality of the image depends on the recording device, the number of pixels used, the levels of light and how the image is stored.

Describe the characters on a keyboard:

Each character on a keyboard has a corresponding ASCII value. Each character pressed is converted into a digital signal, which the computer interprets.

How the computer recognises a letter pressed on the keyboard?

• There is a membrane or circuit board at the base of the keys.

• The CPU in the computer can then determine which key has been pressed.

• The CPU refers to an index file to identify which character the key press represents.

Describe a disadvantage of using keyboards:

They are a relatively slow method of data entry and are also prone to errors.
Frequent use of keyboards can lead to injuries, such as repetitive strain injury (RSI) in the hands and wrists. Ergonomic keyboards can help to overcome this problem - these have the keys arranged differently and are also designed to give more support to the wrists and hands when doing a lot of typing.

How do microphones work?

• When sound is created, it causes the air to vibrate.

• When a diaphragm in the microphone picks up the air vibrations, it also begins to vibrate.

• A copper coil is connected to the diaphragm. As the diaphragm vibrates, the cone moves in and out causing the copper coil to move backwards and forwards.

• This forwards and backwards motion causes the coil to cut through the magnetic field around the permanent magnet, inducing an electric current.

• The electric current is then either amplified or sent to a recording device.

Describe an optical mouse:

An optical mouse is an example of a pointing device. It uses tiny cameras to take 1500 images per second. The optical mouse can work on virtually any surface.

How does an optical mouse work?

• A red LED is used in the base of the mouse and the red light is bounced offthe surface and the reflection is picked up by a complementary metal oxide semiconductor (CMOS).

• The CMOS generates electric pulses to represent the reflected red light and these pulses are sent to a digital signal processor (DSP).

• The processor can now work out the coordinates of the mouse based on the changing image patterns as it is moved about on the surface.

• The computer can then move the on-screen cursor to the coordinates sent by the mouse.

Name the advantages of an optical mouse over a mechanical mouse:

• There are no moving parts, therefore it is more reliable.

• Dirt can't get trapped in any of the mechanical components.

• There is no need to have any special surfaces.

Name the advantages of a wired mouse:

• No signal loss since there is a constant signal pathway (wire)

• Cheaper to operate (no need to buy new batteries or charge batteries)

• Fewer environmental issues (no need to dispose of old batteries).

Describe a 2D Scanner:

2D scanners are used to convert a physical paper copy of a document (Known as hard copy) into a digital format that can be stored and processed by a computer.

How does a 2D Scanner work?

1. The user opens the lid and places the document face down on the glass pane

2. The user will close the lid and press scan

3. A bright light is shone on the document, the light will move from one side of the document to the other

4. From the light passing through the paper an image is produced and sent to a lens

5. This image will then be placed onto a light sensitive sheet which is made up of many pixels, each pixel will record the amount of light or colour that is appearing on it.

6. This data will be stored on the computer as a file in its memory.

Describe an 'Optical Character Recognition':

OCR is the process of converting a scanned image file into a text document that can be edited using a word processor.

How does an OCR work?

OCR works by looking at each line of the document and checking to see if the black and white dots match any characters in the reference file. Each time it detects a match it will add that character to the outputted document.

Describe 3D scanners:

3D scanners scan solid objects and produce a three-dimensional image. Since solid objects have x, y and z coordinates, these scanners take images at several points along these three coordinates. A digital image which represents the solid object is formed. There are numerous technologies used in 3D scanners - lasers, magnetic resonance, white light, and so on.

Describe and explain an application of a 2D Scanner:

Facial recognition: Scanners in airports are used to ensure that people are using the correct passports.

How it works?

1. An image of your face is taken by a camera.

2. Your passport is scanned by a 2d scanner. Specialist facial recognition software will compare the proportions of your face on the passport image and the image taken by the camera. The software will look at things such as: width of your nose, hair line, distance between your eyes and the size of your mouth.

Describe and explain an application of a 3D Scanner:

Computed tomographic (CT):
These scanners are used to create a 3D image of a solid object.

How it works?

This is based on tomography technology, which basically builds up an image of the solid object through a series of very thin 'slices'. Each of these 2D 'slices' make up a representation of the 3D solid object. (Each slice is built up by use of X-rays, radio frequencies or gamma imaging).

What are the three main types of touch screens?

• Capacitive

• Infrared

• Resistive

Describe how capacitive touch screens work:

• Capacitive touchscreens are made with many layers of glass, these glass layers act like capacitors that create an electric field between the glass.

• When a person touches the top layer of glass their finger will change the electric current between the glass layers, the coordinates of where the current changes is sent to a microprocessor that uses the information to calculate where the touch happened.

What the two types of capacitive touch screens?

-Surface
-Projective

Give the advantages of capacitive touch screens:

• Better image clarity than resistive screens, especially in strong sunlight.

• Very durable screens that have high scratch resistance

• Projective capacitive screens allow multi-touch.

Give the disadvantages of capacitive touch screens:

• Surface capacitive screens only work with bare fingers or a special stylus.

• They are sensitive to electromagnetic radiation.

Describe how infrared touch screens work:

Infrared touch screens use a glass screen with an array of sensors and infrared transmitters.
-The sensors detect the infrared radiation. If any of the infrared beams are broken, the infrared radiation reaching the sensors is reduced. The sensor readings are sent to a microcontroller that calculates where the screen was touched.

Give the advantages of infrared touch screens:

• Allows multi-touch facilities.

• Has good screen durability.

• The operability isn't affected by a scratched or cracked screen.

Give the disadvantages of infrared touch screens:

• The screen can be sensitive to water or moisture.

• It is possible for accidental activation to take place if the infrared beams are disturbed.

• Sometimes sensitive to light interference.

Describe how resistive touch screens work:

• Resistive touchscreens are made with two layers, the top layer that the user touches is made from polyester and underneath this layer is a glass layer. These two layers are separated by air or an inert gas (such as argon).

• When the user touches the top layer (polyester) it will bend and make contact with the glass layer, this completes a circuit.

• The position of the touch on the screen is calculated by a microprocessor based on where the circuit was completed.

Give the advantages of resistive touch screens:

• Good resistance to dust and water

• Can be used with bare fingers, stylus and gloved hand.

Give the disadvantages of resistive touch screens:

• Low touch sensitivity.

• Doesn't support multi-touch facility.

• Poor visibility in strong sunlight.

• Vulnerable to scratches on the screen.

What is a an actuator?

An actuator is a mechanical or electromechanical device such as a relay, solenoid or motor used to control or operate something.

What is a light projector?

Projectors are output devices that use light to project an image of the computer screen onto a larger viewing area e.g. a whiteboard on a wall.

What are the two main types of light projectors?

· Digital Light Projectors (DLP)
· Liquid Crystal Display Light Projectors (LCD)

How does a Digital light projector work?

A bright white light source (for example, from a xenon bulb) passes through a colour filter on its way to the DMD chip. The white light is split into the primary colours: red, green and blue - the DLP projector can create over 16 million different colours. The ON and OFF states of each micro mirror are linked with colours from the filter to produce the coloured image.

How does a Liquid Crystal Display Light Projectors work?

• Powerful beam of white light is generated from a bulb or LED.

• This beam of light is then sent to a group of chromatic-coated mirrors; these reflect the light back at different wavelengths.

• When the white light hits these mirrors, the reflected light has wavelengths corresponding to red, green and blue light components.

• These three different coloured light components pass through three LCD screens.

• Consequently, three different versions of the same image are now produced.

• These images are then re-combined using a special prism to produce a full colour image.

• Finally, the image passes through the projector lens onto a screen.

What are the two main types of printers?

· Inkjet Printers
· Laser Printers

Describe an Inkjet printer:

Inkjet printers work by spraying the ink through little nozzles onto the paper. There are two methods used to spray the paint, these two ways are Thermal bubble and Piezo electric.

Describe how a Thermal Bubble printer works:

Tiny resistors create localised heat which makes the ink vaporise. This causes the ink to form a tiny bubble; as the bubble expands, some of the ink is ejected from the print head onto the paper. When the bubble collapses, a small vacuum is created which allows fresh ink to be drawn into the print head. This continues until the printing cycle is completed.

Describe how a Piezoelectric Crystal printer works:

A crystal is located at the back of the ink reservoir for each nozzle. The crystal is given a tiny electric charge which makes it vibrate. This vibration forces ink to be ejected onto the paper; at the same time more ink is drawn in for further printing.

Describe a laser printer:

Laser printers are different to inkjets as they use dry toner rather than liquid ink and they produce a whole page at a time whereas inkjet printers print line by line. How do they work?

Describe how a laser printer works:

1. Paper is drawn in from the paper holding tray

2. A drum inside the printer begins with a positive charge

3. A laser is activated and shone at parts of the drum that will require ink for the printing process. The laser is simply removing the positive charge from certainn areas of the drum

4. Positively charged toner is applied to the drum, this toner will only stick the the negatively charged parts created by the laser

5. The paper, which is negatively charged is rolled past the drum and the toner will stick to the page creating an exact copy of the image / text

6. The paper will now pass a heated fuser which will melt the ink onto the paper

7. The paper will now exit the printer ready for the user and the drum will have its electric charge removed ready for the next print job

Describe an application of a laser printer:

Produce high quality printouts and are very fast when making multiple copies of a document; any application that needs high volume printing would choose the laser printer.

example: poster for advertising.

Describe an application of a inkjet printer:

Used for printing one-off photos or where only a few pages of good quality, colour printing is needed; the small ink cartridges or small paper trays would not be an issue with such applications.

Describe a 3D printer:

3D printers are used to produce solid objects that actually work. The solid object is built up layer by layer using materials such as: powdered resin, powdered metal, paper or ceramic.

How do 3D printers work?

• A design is made using computer aided design (CAD) software.

• The 3D printer is first set up to allow the solid object to be made.

• The finalized drawing is imported into some special software that prepares it in a format that is understood by the 3D printer.

• The solid object is built up layer by layer (often only 0.1 mm thick.

• The object is removed from the printer and is then prepared.

How do LED screens work?

An LED screen is made up of tiny light emitting diodes (LEDs). Each LED is either red, green or blue in colour. By varying the electric current sent to each LED, its brightness can be controlled, producing a vast range of colours.

How do LCD screens work?

LCD screens are made up of tiny liquid crystals. These tiny crystals make up an array of pixels that are affected by changes in applied electric fields. For LCD screens to work, they require some form of backlighting. LCD screens are back-lit using light emitting diode (LED) technology. Use of LED backlighting gives a contrast and brightness range. Before the use of LEDs, LCD screens used cold cathode fluorescent lamp (CCFL) as the back-lit method.

Advantages of LEDs over older CCFL technology:

· LEDs reach their maximum brightness almost immediately.
· LEDs produce a brighter light that improves the colour definition.
· Monitors using LED technology are much thinner than monitors using CCFL technology.
· LEDs last indefinitely.
· LEDs consume very little power which means they produce less heat as well as using less energy.

How do OLEDs work?

Work similarly to LCDs without the use of a backlight. OLED screens have 6 layers, these are:

1. Glass/plastic top layer

2. Cathode layer

3. Emissive layer

4. Conductive layer

5. Anode

6. Glass/plastic bottom layer

Organic films are sandwiched between two charged electrodes (one is a metallic cathode and the other a glass anode). When an electric field is applied to the electrodes, they give off light. This means that no form of backlighting is required.

Describe the advantages of OLEDS:

• The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystal structures used in LEDs or LCDs.

• OLEDs give a brighter light than LEDs.

• OLEDs do not require back lighting like LCD screens OLEDs generate their own light.

• Use much less power than LCD

• They can be made into large, thin sheets

• OLEDs have a very large field of view, about 170 degrees.

What are sensors?

Sensors are input devices which read or measure physical properties from their surroundings. However, computers cannot make any sense of these physical quantities so the data needs to be converted into a digital format. (ADC).

Describe and give an example of a temperature sensor:

Measures temperature of the surroundings by sending signals; these signals will change as the temperature changes.

Examples:
- Control of a central heating system.
-Control/monitor a chemical process.
-Control/monitor temperature in a greenhouse.

Describe and give an example of a moisture sensor:

Measures water levels in, for example, soil.

Examples:
-Control/monitor moisture levels in soil in a greenhouse.
-Monitor the moisture levels in a food processing factory.

Describe and give an example of a humidity sensor:

Measures the amount of water vapour in, for example, a sample of air.

Examples:
-Monitor humidity levels in a building.
-Monitor humidity levels in a factory.
-Manufacturing microchips.
-Monitor/control humidity levels in the air in a greenhouse.

Describe and give an example of a light sensor:

These use photoelectric cells that produce an output depending on the brightness of the light.

Examples:
-Switching street lights on or off depending on light levels.
-Switch on car headlights automatically when it gets dark .

Describe and give an example of an infrared (active) sensor:

Use an invisible beam of infrared radiation picked up by a detector; if the beam is broken, then there will be a change in the amount of infrared radiation reaching the sensor.

Example:
-Turn on car windscreen wipers automatically when it detects rain on the windscreen.
-Security alarm system (intruder breaks the infra- red beam).

Describe and give an example of an infrared (passive) sensor:

Sensors measure the heat radiation given off by an object.

Example:
-Security alarm system (detects body heat).
-Monitor the temperature inside an industrial freezer or chiller unit.

Describe and give an example of a pressure sensor:

A pressure sensor is a transducer and generates different electric currents depending on the pressure applied.

Example:
-Weighing of lorries at a weighing station.
-Measure the gas pressure in a nuclear reactor.

Describe and give an example of an acoustic/sound sensor:

Microphones that convert detected sound into electric signals/pulses.

Examples:
-Pick up the noise of footsteps in a security system.
-Detect the sound of liquids dripping at a faulty pipe joint.

Describe and give an example of a gas sensor:

Use various methods to detect the gas being monitored and produce outputs that vary with the gas levels that are present.

Examples:
-Monitor pollution levels in the air at an airport.
-Monitor oxygen and carbon dioxide levels in a greenhouse.
-Monitor oxygen levels in a car exhaust.

Describe and give an example of a pH sensor:

Measure acidity through changes in voltages in, for example, soil.

-Monitor/control acidity levels in the soil in a greenhouse.
-Control acidity levels in a chemical process.

Describe and give an example of a Magnetic field sensor:

These sensors measure changes in magnetic fields.

Example:
-Detect magnetic field changes (for example, in mobile phones and CD players).
-Used in anti-lock braking systems in cars.

Describe and give an example of an accelerometer sensor:

These are sensors that measure acceleration and motion of an application, i.e. the change in velocity.

Examples:
-Used in cars to measure rapid deceleration and apply air bags in a crash.
-Used by mobile phones to change between portrait and landscape mode.

Describe and give an example of a proximity sensor:

These sensors detect the presence of a nearby object.

Examples:
-Detect when a face is close to a mobile phone screen and switches off screen when held to the ear.

Describe and give an example of a Flow (rate) sensor:

Sensors measure the flow rate of a moving liquid or gas and produce an output based on the amount of liquid or gas passing over the sensor.

Examples:
-Used in respiratory devices and inhalers in hospitals.
-Measure gas flows in pipes (for example, natural gas).

Describe and give an example of a level sensor:

These sensors use ultrasonics: (to detect changing liquid levels in, for example, a tank).
Or capacitance/ conductivity (to measure static levels (for example, height of water in a river).

Examples:
-Monitor levels in a petrol tank in a car.
-In a pharmaceutical process where powder levels in tablet production need to be monitored.
-Leak detection in refrigerant (air conditioning).

What is a Control System? Give an example:

Control systems can take control and alter how a process is altering e.g. turning up fans on an air-conditioning machine because the temperature has become too high.
When the computer is used to control devices it is necessary to use a digital to analogue converter (DAC) since these devices need analogue data to operate in many cases.

Examples:
-Air conditioning / heating systems.
-Traffic light control.
-Automatically turning street lights on and off at night.

What is a Monitoring System? Give an example:

Monitoring systems do not make any changes to the process, instead it simply reports the information / values to the user.

Examples:
-Monitoring a patients vitals in intensive care.
-Checking for intruders in an alarm system.
-Monitoring pollution levels.

How do you answer a control system questions:

1. The (Name the sensor) Sensor is reading the (Insert property) at a (set rate or constantly)

2. The data is converted with an ADC and sent to the microprocessor

3. The microprocessor will compare this data against the pre-defined values that are known to be acceptable.

Control system: If the sensors reading and the pre-defined values do not match. The microprocessor will send a signal to the (Insert device) to adjust the physical properties. This signal must go through a DAC. The system will continue until it is switched off or programmed to do so.

How do you answer a monitoring system questions:

1. The (Name the sensor) Sensor is reading the (Insert property) at a (set rate or constantly)

2. The data is converted with an ADC and sent to the microprocessor

3. The microprocessor will compare this data against the pre-defined values that are known to be acceptable.

Monitoring system: If new data is outside the acceptable range, a warning message is sent to a screen or an alarm is activated. The microprocessor/computer has no effect on what is being monitored - it is simply 'watching' the process.