CS-iGCSE-CIE-Notes

Input Devices

Words in blue don’t study - don’t need to know how the devices work, only which scenarios to use them, their advantages and disadvantages

2D Scanners

The subject is placed on a glass plate where a light will shine over it and illuminate the object. Newer models use xenon lights or LEDs as they can be very bright.A scan head will then move over the subject and produce an image. This image is sent to a lens through a collection of mirrors. The lens will focus the image and send it to a CCD (Charge coupled device) which converts light into an electric current. A charged coupled device has many light-sensitive pixels that produce a charge when light falls onto it. This is how it converts light into an electric, digital image. Software will then produce a digital image. Data extraction processes:1) **OCR (Optical character recognition)

1. Turning the document into an electronic document by recognising the letters into ascii/unicode

2. Scanned text can be converted to text file format

1) OMR (Optical mark recognition)

1. Recognises marks on a document such as on exam scripts

2. Advantages: automated, very fast, reduces human errorAdvantages: Can be higher resolution than a film camera, documents can be sent directly from scanner, converted documents can be edited with softwareDisadvantages: uses a lot of memory, scanner may reduce quality, scanned documents should be high quality2D scanners are widely used in airports to quickly scan passports, or used to scan physical documents. OCR technology allows the images to be processed and manipulated. The holder of the passport’s face can also be compared with a picture of them taken by a camera. **

3D Scanners

Captures data from physical objects at rapid speeds. It produces a three dimensional image by taking pictures of the object from many different angles. The digital image is produced when the pictures form a 3D object. This image can then be sent to a CAD software or 3D printer. Uses: airport security (scanning a human image to detect suspicious objects), replicating existing parts for reverse engineering, CT (computed tomographic) scanners used in x-rays, MRI (magnetic resonance images) for radio frequencies, SPECT (single photon emission computer tomography) for gamma rays. The examples above use tomography technology to produce thin ‘slices’ of the object that get built up one by one until the full object is produced.Advantages: very fast able to capture very large environments in a short amount of time, non-contact data captureDisadvantages: it uses lasers to capture data meaning that it is easily interfered by light

Barcode Scanners

**Barcodes are a method of quick identification of an object or place.A barcode is a collection of light and dark lines with varying thicknesses. These thicknesses create different patterns than represent the numbers 0-9. A red light is flashed onto the barcode using a light emitting diode (LED). The light bounces back from the white bars and is picked up by light sensors (photoelectric cells). The data is then read and converted to binary code. Advantages: fast, efficient, access to information faster, easier to update informationDisadvantages: cannot hold a large amount of data
	Advantages	Disadvantages
	Fast and efficient method of identifying items	Cannot hold large amounts of data
	Faster access to information
	Easier to update information on database		**

QR Code

**(Quick response) Code - the reader will decipher the code and automatically complete an action. QR codes are fast methods of accessing information on the internet. Instead of a sequence of lines, a QR code is a block, a grid, of light and dark squares (pixels). This allows it to hold much more information such as web addresses. QR codes have a number of uses including but not limited to advertisement (QR code on billboards, signs, to promote a certain product, website is very easy to access), automatic access to a website or contact, storing board passes electronically. When being read by a phone, the light and dark squares are processed and converted to readable data. This data is then read by a fitting software and an action is completed.
	Advantages	Disadvantages
	Able to hold much more data than barcodes: 2500 compared to the 25 that barcodes can store	More than 1 QR format is available making it confusing
	It can be scanned from any angle	QR codes may contain malicious software as there is no security on QR codes
	Can be scanned from mobile devices
	Easy access to information
	Incomplete/damaged QR codes can still be scanned successfully		Data and error correction keys are located within and throughout the QR code and they replace corrupted/damaged data with stored backup data**

Microphone

Microphones convert sound waves to an electric current. They’re used to record sounds digitally so that they can be either stored or manipulated. Sound creates **small vibrations in the air. The microphone picks it up via a diaphragm that moves back and forth according to the air’s vibrations. Shown in the diagram, the cone is connected to a copper coil. When the cone moves, it causes the coil to move back and forth creating a magnetic field around the microphone’s permanent magnet. The magnetic field will produce an electric current which is the output of the microphone. This current can then be sent to a computer which converts the analog signal to a digital one and stored/manipulated.  **

Keyboard

Every laptop or desktop computer needs a keyboard. It is one of the main methods a user can interact with the computer; it is a universal data entry device. Keyboards allow users to easily enter data and write more efficiently. A keyboard has many different keys which can represent different **characters. They are arranged on a circuit board. Under each key, the circuit is broken. When pressed, the key will complete the circuit. Once the circuit has been completed, the CPU can calculate the location of the keypress. It then uses an index file to determine the ASCII or unicode of the character, which can then be interpreted as binary. Scancodes are how the computer can identify which key has been pressed. It is a number or sequence assigned to a key. When the computer receives the scancode, it is converted to a unicode character and is displayed.**

Digital cameras

A camera that can produce digital images to be later stored or manipulated in a computer. They can also be internally embedded into a phone or computer. It is controlled by a microprocessor that is able to automatically adjust the settings and quality of the image. For example, it can control the focus, flash, aperture, shutter speed, and size. This is something that older film cameras cannot do. How it works: nWhen light passes through the lens of the camera, it hits millions of light-sensitive sensors arranged in a matrix in the back. The size of this sensor, or the number of pixels it has determines the file size of the image. This is called a CCD (charge coupled device). The sensors convert light into electrical signals, which are converted to digital signals by an ADC. The digital signals are then processed by a microprocessor to form a digital image array. The sensors can also measure colour where different pixels measure red, green, and blue light. 

Optical mouse

An optical mouse is described as a pointing device that allows the user to control the cursor on a computer screen. The user is able to point to any position on the display screen and complete actions. Actions such as selecting, opening & closing programs, scrolling, hovering, and dragging & dropping. They also have left and right click options and some have other buttons. In the image above, the mouse uses a red LED to determine its position. As the mouse moves, light bounces off of the surface it is moving on into a lens which sends the light to a CMOS (also seen on the diagram above). A CMOS is a type of sensor that converts light into electrical signals. These converted electrical signals are then sent to a DSP or (digital signal processor) that is able to calculate the coordinates of the mouse by comparing the current to the previous image patterns. The on-screen cursor would then move according to these coordinates. 

 Touch screens

Touch screens are commonly used in mobile devices so that the user can interact with the device and enter data.  Resistive:**Resistive touch screens are also referred to as ‘hybrid’ touch screens as they utilise the conductive layer of capacitive touch screens. The difference is that there are two conductive surfaces (a flexible plastic layer and a glass bottom layer with conductive coating), and an insulating layer of air between them. When the two surfaces meet, a circuit is completed and the voltage increases. A sensor detects the area where the voltage changed and sends a signal to a microprocessor.
	Advantages	Disadvantages
	More durable	Does not support multitouch
	Waterproof	Slower response
	Works with gloves	Screen visibility poor in bright environments
	Cheaper		It does not support multi touch, and has a slower response timeHowever it is cheaper to manufacture, Capacitive:The human finger has conductive properties that allow electricity to pass through. Capacitive touch screens use this to detect touch and its location. The layers of the touch screen include a conductive surface such as glass. In surface capacitive touch screens, an electric field is created by small voltages applied at each corner. When a finger touches this surface, it disrupts the electric field and is picked up by sensors at the corners of the screen. A microprocessor measures the difference before and after the disruption and calculates the coordinates.  Within projective capacitive touch screens, a grid of electrodes lie under the surface of the screen. This matrix is able to pinpoint the location of the disruption. They are able to detect multiple touch points. The surface of a capacitive touch screen is conductive. An electric field is spread across the screen. Sensors at the corners of the screen detect the electrical field. Due to the conductive properties of a human finger, the charge is transferred to the user, disrupting the field. The coordinates of the disruption is calculated using a microprocessor.
	Advantages	Disadvantages
	More sensitive	Less durable
	Supports multitouch	Expensive
	Screen visibility good in bright environments	Does not work with gloves	Advantages: faster response time, supports multitouchDisadvantages: requires conductive material to detect touch so it cannot be used when wearing gloves, usually more expensive to produceInfra-red:Infra-red transmitters are arranged in a grid-like pattern across the screen. The sensors on the opposite of the transmitters detect radiation from the transmitters. When a finger disrupts the transmitters, the radiation is weakened and the sensors alert a microcontroller of this change. This is how the screen is able to point where it was touched. Infra-red touch screens support multi-touch.
	Advantages	Disadvantages
	Can use gloves (only optical)	Expensive
	Durable	Heat-sensitive only detects fingers
	Broken screen does not affect it
	Supports multitouch		**

Output Devices

Actuator

*Actuators are mechanical or electromechanical devices that cause a physical movement from energy and signals. They can start or stop a process or open or close a valve. They are able to control single-function devices.  Solenoid example

• Electricity and magnetism are connected

• Solenoids turn electricity into a magnetic field

• This causes linear motion that allows operating a valve and rotary solenoids can produce rotational motion using a cylindrical coil**

DLP (Digital Light Processing) Projector

This type of light projector utilises a **DMD (digital micromirror device) chip to project images onto a screen. Millions of micro mirrors are arranged in a matrix on the chip. The mirrors can tilt to reflect the light from a source to switch ‘on’ or ‘off’. The smaller and more of these mirrors are on the chip, the higher the resolution will be. To turn ‘on’ a mirror, it tilts towards the light to reflect it. When it isn’t, it becomes dark and is recognised as ‘off’. They can switch between these states thousands of times a second to create an illusion of a wider range of values known as the greyscale. About 1024 different shades of grey can be produced.Colour filters are applied to the light source to produce different colours. The image created by the DMD is passed into a lens which projects the focused image onto a screen.Inside the projector:Light source (white light) → Condensing lens → Colour filter → Shaping lens → DMD chip → Lens → Screen
	Advantages	Disadvantages
	High longevity/reliability	Images tend to suffer from ‘shadows’ when displaying moving images
	Smaller and lighter than an LCD projector	colour saturation is worse than LCD projector
	Quiet		Applications of projectors:* Presenting to a large audience

• Boardrooms

• Cinemas**

Inkjet Printer

**Process printing using an inkjet printer: 1) Data about the document is sent to the printer

1) The printer’s driver checks that it’s in a format that the printer can understand

2) Another check makes sure that the printer is available

3) The data from step 1 is sent and stored in a temporary memory called a printer buffer

4) A paper feed uses rollers to send paper through the printer

5) A stepper motor and belt moves the print head across the page line by line

6) The printhead has a lot of nozzles which spray droplets of ink onto the paper

7) The nozzles spray ink from cartridges to create text or images

8) After the line has finished it moves very slightly in the position of the next line

9)  If the printer buffer has more data the next line is printed until no more data is left

10)  After the printer buffer has been emptied, the printer will alert the CPU in the computer that it requests more data about the document until the whole document is printedThe ink droplets can be created using two different methods: Thermal bubble: The ink is heated until vaporisation and forms a small bubble. As it expands, it spits out more ink from the nozzle onto the paper. The bubble is pushed through the nozzle until it pops onto the paper. When it pops, it creates a small vacuum that sucks more ink out of the cartridge into the nozzle. Piezoelectric: A crystal at the back of the ink reservoir is given a small charge that causes it to vibrate. The vibration forces the ink onto the paper, and forces more ink into the nozzle. Uses: printing very low numbers of high quality photos as the ink cartridges are quite small.
	Advantages	Disadvantages
	Cheaper	Slower
	No heat applied therefore it can print on a variety of materials	Printed text quality is not as good as laser printers
	Very good photographic quality	Ink cartridges can be expensive	**

Laser Printer

The ink in inkjet printers is liquid, however laser printers use powder ink and static electricity to stick it onto the paper. Uses:** used when a large print job of high quality printouts are required
	Advantages	Disadvantages
	Faster than inkjet printers as they print an entire page in one go	Reduced photographic quality compared to inkjet printers
	High volume printing	Typically very heavy
	Smaller and lighter than an LCD projector	Expensive - high initial cost
	Quiet	Toner is expensive
	Text is very sharp		https://www.computerlanguage.com/results.php?definition=laser+printerProcess of printing using a laser printer:1) Data from the computer is sent to the printer

1) The printer’s driver checks that it’s in a format that the printer can understand

2) Another check makes sure that the printer is available

3) The data from step 1 is sent and stored in a temporary memory called a printer buffer

4) Within the printer there is a printing drum that has a positive charge - it rotates as a laser with a negative charge targets areas that make the print (the areas the ink is supposed to be) and gives them a negative charge leaves a positive charge on the paper

5) The drum is then coated with positively charged powder ink that is attracted and sticks onto the negatively charged areas

6) The drum then rolls over a negatively charged sheet of paper

7) A toner from the drum sticks onto the paper and produces a copy to be sent to the printer

8) After the ink as been applied the paper a charge is applied to let the drum and paper separate

9)  Then the paper is sent through a fuser that melts the ink permanently on the page

10)  Finally, a discharge lamp removes the charge from the drum ready for the next print**

LED (Light Emitting Diode) Screen

**An LED screen is made of many small LEDs (light emitting diodes). Every LED is either red, blue, or green. Altogether it appears as white light and they are arranged in a pattern closely together. By controlling the amount of electrical current and strength of the LEDs, it can generate a variety of colours. LED screens are usually used for large outdoor displays such as on buildings, billboards, and large signs.
	Advantages	Disadvantages
	No light leak due to no backlight	Expensive
	Sharper colours	Quality and colours may change overtime
	Lower power consumption
	Long lifespan
	Brighter and sharper images		**

LCD (Light Crystal Display) Projector

* The projector has: A powerful lamp or LED that generates a beam of white light

• Chromatic-coated mirrors (dichromic mirrors) each either red, green, or blue

• Three liquid crystal panels (LCD screens) made up of thousands of pixels that can either block or let light pass through (produces a monochromatic image as there is only one colour showing through)

• LCD screens then combine and overlay their images to produce a full-colour image in a specialised prism known as a dichroic combiner cube

• It passes through the projector lens to project the image onto the screen
  	Advantages	Disadvantages
  	Better saturation of colours	Shorter lifespan
  	Brighter and sharper colours	Quality and colours may change overtime
  	Energy efficient	LCD technology yellows overtime
  	Brighter and sharper images		**

LCD (Light Crystal Display) Screen

**LCD screens differ from LED screens in the way that they require a backlight. The individual pixels do not produce any light on their own. The backlight uses LEDs which gives the screen good contrast and brightness. However this may cause light leaks. Small liquid crystals are arranged in a matrix to represent the pixels of an image. When an electrical charge is applied to them, they can change its shape to either block or diffuse light, creating images and patterns on the screen. The pixels can have colour filters of red, blue, and green, which it can use to make many different colours on the colour spectrum.
	Advantages	Disadvantages
	Long lifespan	Lower saturation of colours
	No screen-bur	Unable to produce sharp blacks or dark greys
	Energy efficient	Light leak
	Better resistance to direct sunlight than LED screens	Limited viewpoints	LCD screens used to be the most popular phone screen. An advantage of this is resistance to direct sunlight because of the backlit feature of LCD screens. However, many phone brands now offer LED screens and OLED screens. **

3D Printers

3D printers are based on inkjet and laser printers. The product is usually made of powdered resin, powdered metal, paper, or ceramic. These structures are built using many thin layers of material about 0.1mm thick. Direct 3D printing: Based off of inkjet printing, a moving printhead releases the chosen material and builds the object up layer by layer. The print head can move left, right, up, and down. Binder 3D printing: This uses two ‘passes’. The first layer is a dry powder and the second pass sprays a ‘binder’ which is some kind of glue to solidify the powder.Newer 3D printers use lasers and UV light to harden and solidify the objects. Computer aided design is used to design a solid object to be printed. The drawing is then sent to a software that prepares it to be 3D printed. 3D printers are used in many different aspects such as creating replacement parts as the component can be as specific and custom as the user likes, industrial and construction manufacturing, art, and prototyping. It is also typically used for prototyping components for both personal and commercial use, human prosthetics, and medical aid.The drawback to 3D printers is the high initial cost. 

Speakers

Similar to a microphone, it has a cone, coil, and permanent magnet. Process:**1) A DAC (digital to analogue converter) changes the sound file to an electric current

1) This current enters an amplifier so that it is large enough to power a loudspeaker

2) The current is sent through a coil that is wrapped around an iron core with a permanent magnet near the coil

3) This current induces a magnetic field and causes the iron to be attracted to the magnet

4) This vibrates the core depending on the current and in turn vibrates a cone that moves the air, and produces sound wavesApplications of speakers:* Cinemas**

Sensors

3.2.3A sensor is an electrical device that can read and measure the physical properties of an environment. It is an ADC meaning it converts analogue to digital signals that can be sent to a processor. Sensors are used in many other electronic devices all measuring different properties. They are used to either monitor or take part in controlling a factor through a feedback loop. However, sensors can not only output digital signals but also analogue signals. Rather than  a binary 1 or 0, it outputs a continuous stream of values which vary based on the environment Photovoltaic - ambient light

Temperature

The most common types of temperature sensors are Negative Temperature Coefficient (NTC) Thermistors, Resistance Temperature Detectors (RTDs), Thermocouples, and Semiconductor-Based Sensors. They each have varying levels of tolerance and accuracy. It measures the surrounding temperature through signals. Used for heating systems, temperature control

Moisture

Measures the water levels in a substance based on the electrical resistance of it.Used for measuring moisture in a greenhouse (soil)

Humidity

Measure the amount of water vapour in air based on the conductivity of the sampleUsed for monitoring humidity in a building, factory, greenhouse

Light

Uses photoelectric cells that produce a weaker or stronger output based on the brightness of its surroundings.Used for streetlights, car headlights

Infrared (active)

An invisible beam of infrared light is picked up by a detector. When the beam is interfered with for example an object, the amount of infrared light hitting the detector changes.Used in alarm systems

Infrared (passive)

Heat radiation from an object from humans or the temperature of a fridgeUsed for security systems, monitoring temperature of a fridge

Pressure

A transducer produces different electrical signals based on pressure appliedTransducer** - a device that can converts energy forms from one to anotherUsed for weighing object, measuring gas pressure**

Sound/acoustic

Microphones that send detected sounds as signalsUsed in consumer electronics such as phones, or home appliances that require sound level recognition, used for security, and detecting dripping at a faulty pipe joint

Gas

Sensors designed to detect specific types of gas by comparing the sample to data from the actual gas. A device produces an output based on a method to detect a type of gas or characteristics of a type of gas. Monitors pollution, gas levels in greenhouses, oxygen levels in a car exhaust

pH

Acidity changes voltage which a device picks upMonitor soil in a greenhouse, control acidity levels in chemical processes

Magnetic field

Measures changes in a magnetic field and produces signals when changes are detected.Used in mobile phones, CD players, brake systems in cars.

Accelerometer

Measures the acceleration or motion of an object. Voltage changes when acceleration changes, and this is measured by a piezoelectric cell which produces different outputs depending on the voltage).Used in cars (airbags), mobile phones (portrait or landscape).

Proximity

Detect objects nearbyUsed in face ID on mobile phones

Flow (rate)

Measure flow rate of moving liquids or gases. Sensor produces outputs depending on the amount of liquid that passes over it. Used in hospitals (respiratory devices), measures gas flow in pipes

Level

Measures liquid levels in a container. It uses ultrasonics, capacitance, or conductivity.Measures height of water in a river, petrol tank of a car, leak detection in air conditioning.

Some additional terms

Microprocessors are small integrated circuits on a single chip. They contain all the functions of  CPUMicrocontrollers are integrated systems on a single chip that can perform very specific functions. They contain one or more processors (CPUs), memory, and input/output methods.Embedded systems are a combination of software and hardware designed for a specific function. They are feedback oriented systems that take analogue or digital data from either an operator or sensor and produce an output. These are used in medicine, cars, telecommunication, home appliances, and other consumer and industrial devices. 

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