Chpm3 Flashcards
1
Q
The central processing unit (CPU)
A
(also known as a microprocessor or processor) is central to all modern computer systems (including tablets and smartphones). The CPU is very often installed as an integrated circuit on a single microchip. The CPU has the responsibility for the execution or processing of all the instructions and data in a computer application.
2
Q
CPU consist of
A
Control unit
Arithmetic and logic unit ALU
Register and buses
3
Q
The von Neumann architecture had the following main nove
ompute
features (none of which were avaitable in computers prior to the mid-1940s)
A
the concept of a central processing unit (CPU or processor)
* the CPU was able to access the memory directly
» computer memories could store programs as well as data
stored programs were made up of instructions which could be executed in sequential order
4
Q
Arithmetic & Logic Unit (ALU)
A
allows the required arithmetic (e.g. +, - and shifting) or logic (e.g. AND, OR) operations to be carried out while a program is being run; it is possible for a computer to have more than one ALU to carry out specific functions. Multiplication and division are carried out by a sequence of addition, subtraction and left or right logical shift operations.
5
Q
Control u it
A
reads an instruction from memory. The address of the location where the instruction can be found is stored in the Program Counter (PC). This instruction is then interpreted using the Fetch-Decode-Execute cycle (see later in this section). During that process, signals are generated along the control bus to tell the other components in the computer what to do. The control unit ensures synchronisation of data flow and program instructions throughout the computer. A
6
Q
system clock
A
is used to produce timing signals on the control bus to ensure this vital synchronisation takes place - without the clock the computer would simply crash!
7
Q
The ram holds
A
The RAM holds all the data and programs needed to be accessed by the CPU. The RAM is often referred to as the Immediate Access Store (IAS). The CPU takes data and programs held in backing store (e.g. a hard disk drive) and puts them into RAM temporarily. This is done because read/write operations carried out using the RAM are considerably faster than read/write operations to backing store; consequently, any key data needed by an application will be stored temporarily in RAM to considerably speed up operations.
8
Q
Registered
A
Registers can be general or special purpose. We will only consider the special purpose registers.
9
Q
CIR current instruction register
A
this register stores the current instruction being decoded and executed
10
Q
ACC accumslotst
A
this register is used when carrying out ALU calculations; it stores data temporarily during the calculations
11
Q
MAR memory address register
A
this register stores the address of the memory location currently being read from or written to
12
Q
MDR memory data register
A
this register stores data which has just been read from memory or data which is about to be written to memory
13
Q
PC program counter
A
this register stores the address where the next instruction to be read can be found
14
Q
What are the three buses
A
Control bus
Address bus
Data bus
15
Q
Partition
A
The computer memory is made up of a number of partitions, each partition consists of an address and it’s contenteds
16
Q
The address in partitions
A
The address will uniquely identify every location in the memory and the contents will be the binary value stored in each location
17
Q
Let us now considerate examples of how the MAR and MDR registers can be use when carrying out a read and write operation to and from memory:
A
the address of location 1111 0001 to be read from is first written into the
MAR (memory address register):
read signal’ is sent to the computer memory
» the contents of memory location 1111 0001 are then put into the MDR (memory data register):
Now let us now consider the WRITE operation. Again, we will use the memory section shown in Table 3.2. Suppose this time we want to show how the value 1001 0101 was written into memory location 1111 1101:
» the data to be stored is first written into the MDR (memory data register):
this data has to be written into location with address: 1111 1101: so this
address is now written into the MAR:
finally, a write signal’ is sent to the computer memory and the value 10010101 will then be written into the correct memory location.
18
Q
Input and output devices
A
They are the main method of entering data into and getting data out of computer systems.
19
Q
Input devices
A
Input devices convert external data into a form the computer can understand and can then process (e.g. keyboards, touch screens and microphones).
20
Q
Output devices
A
Output devices show the results of computer processing in a human understandable form (e.g. printers, monitors and loudspeakers).
21
Q
System busses
A
(yetem) buses are used in computers as parallel transmission components; each the von the bus transmits one bit of era ta. heal ate three common buses used in the von Neumann architecture known as: address bus, data bus and control bus.
22
Q
System busses
A
(yetem) buses are used in computers as parallel transmission components; each the von the bus transmits one bit of era ta. heal ate three common buses used in the von Neumann architecture known as: address bus, data bus and control bus.
23
Q
Address bus
A
As the name suggests, the address bus carries addresses throughout the computer system. Between the CPU and memory, the address bus is unidirectional (i.e, bits can travel in one direction othe a this prevents addresses being carried back to the CPU, which would ee tin undesirable feature.
24
Q
The wider the bus
A
The more memory locations that can be directly addressed at any given time
25
Data bus
The data bus is bidirectional (allowing data to be sent in both directions along the bus). This means data can be carried from CPU to memory (and vice versa) and to and from input/output devices. It is important to point out that data can weath address, an instruction or a numerical value As wipine address bus, the with of the data bus is important; the wider the bus the larger the word length a singan be transported. (A word is a group of bits which can be regarded as a single unit e.g. 16-bit, 32-bit or 64-bit word lengths are the most common.)
Larger word lengths can improve the computer's overall performance.
26
Control bus
The control bus is also bidirectional. It carries signals from the control unit (CU) to all the other computer components. It is usually 8-bits wide. There is no real need for it to be any wider since it only carries control signals.
27
Fevtch decode execute cycle
To carry out a set of instructions, the CPU first of all fetches some data and instructions from memory and stores them in suitable registers. Both the address bus and data bus are used in this process. Once this is done, each instruction Fetesto be decoded before finally being executed. This is all known as the Fetch-Decode-Execute cycle.
28
Fetch
Both data and instruction can be stored in MDR. In the Fetch-Decode-Execute cycle, the next instruction is fetched from the memory address currently stored in the MAR and the instruction is stored in the MDR. The contents of the MDR are then copied to the Current Instruction Register (CIR). The pt is then incremented (increased by 1) so that the next instruction can be then be processed.
29
Decode
The instruction is then decoded so that it can be interpreted in the next part o the cycle.
30
Execute
The CPU passes the decoded instruction as a set of control signals to the appropriate components within the computer system. This allows each instru to be carried out in its logical sequence.
31
Fetch decode execute cycle with the von Neumann model
Any instructions ?
The Program Counter (PC) contains the address of the memony location of the next instruction which has to be fetched
This address is then copied from the PC to the memory address register
(MAR); this is done using the address bus
The contan chico a the memory location (address) contained in
MAR are then copied temporanly into the memory data register (MDR)
The contents finstruction) of the MOR are then copied and placed into the
Current instruction Register (CIR)
The value in the PC is then incremented by 1 so that it now points to the
next instruction which has to be fetched
The instruction is finally decoded and then executed by sending out signals (via the control bus) to the various components of the computer system
32
Role of the system clock
The clock defines the clock cycle that synchronises all computer operations. As mentioned earlier, the control bus transmits timing signals ensuring everything is fully synchronised.
33
By increasing clock speed
increasing clock speed, the processing speed of the computer is also increased (a typical current value is 3.5 GHz
34
Although the speed of the computer may have been increased
Although the speed of the computer may have been increased, it isn't possible to say that a computer's overall performance is necessarily increased by using higher clock speed.
35
Factors to considered
Overclocking is a factor to consider. The clock speed can be changed by accessing the BIOS (Basic Input/Output Systempe and altering the settings.
However, using a clock speed higher than the computer was designed for can lead to problems,
36
Problems that can be caused by using a higher clock speed than the computer is designed to handle,
execution of instructions outside design limits can lead to seriously
unsynchronised operations (i.e. an instruction is unable to complete in
time before the next one is due to be executeds - the computer would frequently crash and become unstable
overclocking can lead to serious overheating of the CPU again leading to unreliable performance.
37
The use of cache memories can also improve
3 The use of cache memories can also improve CPU performance.
38
Ram and cache memory
Unlike RAM, cache memory is located within the CPU itself, which means it has much faster data access times than RAM. Cache memory stores frequently used instructions and data that need to be accessed faster, which improves CPU performance.
39
CPU wishes to read memory
When a CPU wishes to read memory, it will first check out the cache and then move on to main memory/RAM if the required data isn't there.
The larger the cache memory size the better the CPU performance.
40
The use of a different number of cores
4 The use of a different number of cores can improve computer performance.
One core is made up of an ALU, a control unit and the registers. Many computers are dual core (the CPU is made up of two cores) or quad core (the CPU is made up of four cores). The idea of using more cores alleviates the need to continually increase clock speeds.
41
Doubling the number of cores
However, doubling the number of cores doesn't necessarily double the computer's performance since we have to take into account the need for the CPU to communicate with each core; this will reduce overall performance.
42
Dual core
with a dual core the CPU communicates with both cores using one channel reducing some of the potential increase in its performance:
43
Quad core
with a quad core the CPU communicates with all four cores using six channels, considerably reducing potential performance:
44
these factors need to be taken into account when considering computer performance.
increasing bus width (data and address buses) increases the performance and speed of a computer system
» increasing clock speed will potentially increase the speed of a computer
computer's performance can be changed by altering bus widtt
cock speen
" use co merries can also speed up a CPUs performance.
45
In a computer system, instructions are a set of operations which are decoded in sequence.
Each operation will instruct the ALU and CU (which are part of the CPU). An operation is made up of an opcode and an operand.
46
In a computer system, instructions are a set of operations which are decoded in sequence.
Each operation will instruct the ALU and CU (which are part of the CPU). An operation is made up of an opcode and an operand.
47
opcodes that can be used.
opcodes that can be used; this is known as the instruction set.
48
All software running on a computer will contain a set of
Instructions
49
The Fetch-Decode-Execute cycle is the
sequence of steps used by the CPU to process each instruction in sequence.
50
Instructions
instruction sets are the low-level language instructions that instruct the CPU how to carry out an operation. Program code needs interpreters or compilers to convert the code into the instruction set understood by the computer. Some examples of instruction set operations include: ADD, JMP, LDA, and so on.)
51
Embedded system
An embedded system is a combination of hardware and software which is designed to carry out a specific set of functions. The hardware is electronic. electrical or electro-mechanical.
52
Embedded system can be based on
this has a CPU in addition to some RAM and ROM and other peripherals all embedded onto one single chip (together they carry out a specific task)
microprocessor:
integrated circuit which only has a CPU on the chip (there is no RAM, ROM or peripherals - these need to be added)
system on chips (SoC):
this may contain a microcontroller as one of its components they almost always will include CPU. memory. input/output (1/0) ports and secondary storage on a single microchipl
53
Embedded system
When installed in a device, either an operator can input data manually (for example, select a temperature from a keypad or turn a dial on an oven control panel) or the data will come from an automatic source, such as a sensor. This sensor input will be analogue or digital in nature, for example, inputs such as oxygen levels or fuel pressure in a car's engine management system. The output will then carry out the function of the embedded system by sending signals to the components that are being controlled (for example, increase the power to the heating elements in an oven or reduce fuel levels in the engine).
54
Depending on the device, embedded systems are either
programmable or non-programmable. Non-programmable devices need, in general, to be replaced if they require a software upgrade.
55
Programmable devices permit upgrading by two methods:
» connecting the device to a computer and allowing the download of updates t the software (for example, this is used to update the maps on a GPS system used in a vehicle
" automatc updtes ti w:.tlteor.cotorginanagenetroy/
for exame e, mates mode cars allow updates to engine management systo, and other components via satellite link).
56
Benefits of devices being controlled using embedded systems
They are small in size and therefore easy to fit into devices
Compared to other systems, they are relatively low cost to make
They are usually dedicated to one task allowing simple interfaces and often no requirements for an operating system
They consume little power
They can be controlled remotely using a mobile phone
Very fast reaction to changing input
With mass production comes reliability
57
Drawbacks of embedded systems
It can be difficult to upgrade some devices to take advantages of new technology
Troubleshooting faults in the device becomes a specialist task
Although the interface can appear to be more simple more confusing
Any device that can be accessed I’ve the internet is also open to hackers and viruses
Due to difficult in upgrading and fault finding devices are often just thrown away rather than being repaired
Can lead to an increase in the throw away society if devices are discarded just because they have become out of date
58
Because embedded systems can be commected to the inten
et 1 is seting t
control them remotely using a smartphone of computer. For example, setting the
central heating system to swit Shar or orf whte away from home or remote
instructing a set top ox to witch a televisibile agramme. Since embedded systems are dedicated to a specific set of tasks, engineers can optimise their designs to reduce the physical size and cost of the devices. The range of applications are vast, ranging from a single microcontroller (for example, in an MP3 player) to a complex array of multiple units (for example, in a medical imaging system).
59
It is worth mentioning here that a computer is not an example of an embedded system.
It is worth mentioning here that a computer is not an example of an embedded system. Computers are multi-functional (that is, they can carry out many different tasks which can be varied by using different software) which means they can't be classed as embedded systems.
60
Examples of the use of embedded systems
Motor vehicles
Modern cars have many parts that rely on embedded systems to function correctly. Figure 3.7 shows some of the many components that are controlled in this way.
61
Set top box
record example, a set-top box uses an embedded system to allow, for example, re the us and playback of television programmes. This can be operated remotely in the user when not at home using an intermes enabled device or by using the furface panel when at home. The embedded system will look after many of the fusctions involving inputs from a number of sources suih as a Solid State Device (SSD) (where television programmes can be stored or retrieved) or a satellite signal (where it will be necessary to decode the incoming signal).
62
Embedded systems in security
The security code is set in RAM and the alarm activated or deactivated using the keypad. Data from sensors is sent to the controller which checks against values stored on the SSD (these settings are on SSD rather than RAM in case
63
An output can be a signal
To flash lights, sound an alarm or send a message to the home owner via their mobile phone
The home owner can interface with the system remotely if necessary
64
Lighting embedded systems
Embedded systems are used in modern sophisticated lighting system from a simple home use to major architectural lightning systems
System needs to control lighting taking into account the time of the day of the week
Whether the room is occupied
The brightness of the natural light
65
Vending systems
66
Vending machines make considerable use of embedded systems.
They usually use microcontrollers to control a number of functions that we all associate with vending machines:
At the heart of the vending machine is an embedded system in the form of a microcontroller. Inputs to this system come from the keypad (item selection) and from sensors (used to count the coins inserted by the customer, the temperature inside the machine and a ‘tilt sensor’ for security purposes).
67
The outputs of a vending machine
» actuators to operate the motors, which drive the helixes (see figure below) to give the customers their selected item(s)
» signals to operate the cooling system if the temperature is too high
» item description and any change due shown on an LCD display panel
» data sent back to the vending machine company so that they can remotely
check sales activity (which could include instructions to refill the machine) without the need to visit each machine.
68
Washing machines
They all come with a keypad or dials that are used to select the temperature, wash cycle or cooking duration. This data forms the input to the embedded system, which then carries out the required task without any further human intervention. As with other devices, these ‘white goods’ can also be operated remotely using an internet-enabled smartphone or computer.
69
Barcode scanners (readers
Input device
A barcode is a series of dark and light parallel lines of varying thickness. The numbers 0 to 9 are each represented by a unique series of lines. Various barcode methods for representing these digits exist. The example we shall use adopts different codes for digits appearing on the left and for digits appearing on the right of the barcode:
70
Each digit in the barcode is represented by
bars of 1 to 4 blocks thick as shown in Figure 3.15. Note there are different patterns for digits on the left-hand side and for digits on the right-hand side
71
So 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 dark areas reflect little or no light, which allows the bars to be read
» the reflected light is read by sensors (photoelectric cells)
» as the laser or LED light is scanned across the barcode, a pattern is generated,
which is converted into digital data – this allows the computer to understand
the barcode
» for example: the digit ‘3’ on the left generates the pattern:
(where L = light and D = dark), this has the binary equivalent of: (where L = 0 and D = 1).
72
Keypad
Input
to key in the number of same items bought; to key in a weight, to key in the number under the barcode if it cannot be read by the barcode reader/scanner
73
Screen/ monitor
to show the cost of an item and other information
74
Speaker
Input
to make a beeping sound every time a barcode is read correctly; but also to make another sound if there is an error when reading the barcode
75
Printer
Input
to print out a receipt/itemised list
76
Card reader/ chip and pin
Input
to read the customer’s credit/debit card (either using PIN or contactless
77
Touchscreen
Input
to select items by touching an icon (such as fresh fruit which may be sold loose without packaging)
78
So the barcode has been read, then what happens?
the barcode number is looked up in the stock database (the barcode is known as the key field in the stock item record); this key field uniquely identifies each stock item
» 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 (or point
of sale terminal (POS))
» 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
LD DDDL D
Input/output device
How it is used
keypad
to key in the number of same items bought; to key in a weight, to key in the number under the barcode if it cannot be read by the barcode reader/scanner
speaker
to make a beeping sound every time a barcode is read correctly; but also to make another sound if there is an error when reading the barcode
card reader/chip and PIN
to read the customer’s credit/debit card (either using PIN or contactless)
touchscreen
to select items by touching an icon (such as fresh fruit which may be sold loose without packaging)
or equal to this value, more stock items are automatically ordered
once an order for more stock items is generated, a flag is added to the record to stop re-ordering every time the stock item barcode is read
» when new stock items arrive, the stock levels are updated in the database.
79
Advantages to the management of using barcodes
» much easier and faster to change prices on stock items
» much better, more up-to-date sales information/sales trends
» no need to price every stock item on the shelves (this reduces time and cost
to the management)
» allows for automatic stock control
» possible to check customer buying habits more easily by linking barcodes to,
for example, customer loyalty cards.
80
Advantages to the customers of using barcodes
» faster checkout queues (staff don’t need to remember/look up prices of items) » errors in charging customers is reduced
» the customer is given an itemised bill
» cost savings can be passed on to the customer
» better track of ‘sell by dates’ so food should be fresher.
81
Quick response (QR) codes
Another type of barcode is the quick response (QR) code. This is made up of a matrix of filled-in dark squares on a light background. For example, the QR code in Figure 3.17 is a website advertising rock music merchandise. It includes a web address in the code.
QR codes can hold considerably more information than the more conventional barcodes described earlier.
82
Description of QR codes
A QR code consists of a block of small squares (light and dark) known as pixels. It can presently hold up to 4296 characters (or up to 7089 digits) and also allows internet addresses to be encoded within the QR code. This compares to the 30 digits that is the maximum for a barcode. However, as more and more data is added, the structure of the QR code becomes more complex.
» 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.
83
Because of modern smartphones and tablets, which allow internet access on the move, QR codes can be scanned anywhere. This gives rise to a number of uses:
» advertising products (for example, the QR code in Figure 3.17)
» giving automatic access to a website or contact telephone number
» storing boarding passes electronically at airports and train stations
84
By using the built-in camera on a mobile smartphone or tablet and by downloading a QR app (application), it is possible to read QR codes on the move using the following method:
» 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 on the mobile phone or tablet automatically reads 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 (or if a telephone
number was embedded in the code, the user will be sent to the phone
app )
» if the QR code contained a boarding pass, this will be automatically sent to
the phone/tablet.
85
Advantages of QR codes compared to traditional barcodes
» 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 – normal barcodes contain almost no data redundancy (data which is duplicated) therefore it isn’t possible to guard against badly printed or damaged barcodes
» QR codes are easier to read; they don’t need expensive laser or LED (light emitting diode) scanners like barcodes – they can be read by the cameras on smartphones or tablets
» It is easy to transmit QR codes either as text messages or images
» It is also possible to encrypt QR codes which gives them greater protection
than traditional barcodes.
86
Disadvantages of QR codes compared to traditional barcodes
» More than one QR format is available
» QR codes can be used to transmit malicious codes – known as attagging. Since
there are a large number of free apps available to a user for generating QR codes, that means anyone can do this. 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 (for example, photographs, address book, stored passwords, and so on). The user could also be sent to a fake website or it is even possible for a virus to be downloaded.
87
New developments
Newer QR codes (called frame QR codes) are now being used because of the increased ability to add advertising logos (see Figure 3.19). Frame QR codes come with a ‘canvas area’ where it is possible to include graphics or images inside the code itself. Unlike normal QR codes, software to do this isn’t usually free.
88
Digital cameras
Digital cameras have essentially replaced the more traditional camera that used film to capture the images. The film required developing and then printing before the photographer could see the result of their work.
This made these cameras expensive to operate since it wasn’t possible to delete unwanted photographs.
Modern digital cameras simply link to a computer system via a USB port or by using Bluetooth (which enables wireless transfer of photographic files).
89
These 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 » and so on.
90
What happens when a photograph is taken
» theimageiscapturedwhenlightpassesthroughthelensontoalight-sensitive cell; this cell is made up of millions of tiny sensors which are acting as photodiodes (i.e. charge couple devices (CCD) which convert light into electricity)
» each of the sensors are often referred to as pixels (picture elements) since they are tiny components that make up the image
» 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 (now in a digital format); for example, an 8-bit ADC gives 28 (256) possible brightness levels per pixel (for example, brightness level 01110011)
92
3.2 Input and output devices
» apart from brightness, the sensors also measure colour which produces another binary pattern; most cameras use a 24-bit RGB system (each pixel has 8 bits representing each of the 3 primary colours), which means each pixel has a red value (0 to 255 in denary), a green value (0 to 255) and a blue value (0 to 255); for example, a shade of orange could be 215 (red), 165 (green) and 40 (blue) giving a binary pattern of 1101 0111 1010 0101 0010 1000 (or D7A528 written in hex)
Charge coupling device
91
What happens when a photograph is taken
» theimageiscapturedwhenlightpassesthroughthelensontoalight-sensitive cell; this cell is made up of millions of tiny sensors which are acting as photodiodes (i.e. charge couple devices (CCD) which convert light into electricity)
» each of the sensors are often referred to as pixels (picture elements) since they are tiny components that make up the image
» 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 (now in a digital format); for example, an 8-bit ADC gives 28 (256) possible brightness levels per pixel (for example, brightness level 01110011)
92
3.2 Input and output devices
» apart from brightness, the sensors also measure colour which produces another binary pattern; most cameras use a 24-bit RGB system (each pixel has 8 bits representing each of the 3 primary colours), which means each pixel has a red value (0 to 255 in denary), a green value (0 to 255) and a blue value (0 to 255); for example, a shade of orange could be 215 (red), 165 (green) and 40 (blue) giving a binary pattern of 1101 0111 1010 0101 0010 1000 (or D7A528 written in hex)
Charge coupling device
92
Keyboard
Keyboards are by far the most common method used for data entry. They are used as the input devices on computers, tablets, mobile phones and many other electronic items.
The keyboard is connected to the computer either by using a USB connection or by wireless connection. In the case of tablets and mobile phones, the keyboard is often virtual or a type of touch screen technology.
93
Keyboard
Keyboards are by far the most common method used for data entry. They are used as the input devices on computers, tablets, mobile phones and many other electronic items.
The keyboard is connected to the computer either by using a USB connection or by wireless connection. In the case of tablets and mobile phones, the keyboard is often virtual or a type of touch screen technology.
94
There is a membrane or circuit board at the base of the keys
» In Figure 3.25, the ‘H’ key is pressed and this completes a circuit as shown
» The CPU in the computer can then determine which key has been pressed
» TheCPUreferstoanindexfiletoidentifywhichcharacterthekeypressrepresents » Each character on a keyboard has a corresponding ASCII value (see Chapter 1).
95
Microphones
Microphones
Microphones are either built into the computer or are external devices connected through the USB port or using Bluetooth connectivity. Figure 3.26 shows how
a microphone can convert sound waves into an electric current. The current produced is converted to a digital format so that a computer can process it or store it (on, for example, a CD)
96
How microphones work
When sound is created, it causes the air to vibrate.
» When a diaphragm in the microphone picks up the air vibrations, the
diaphragm also begins to vibrate.
» A copper coil is wrapped around the cone which 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. The
electric current is analogue in nature.
97
Optical mouse
An optical mouse is an example of a pointing device. It uses tiny cameras to take 1500 images per second. Unlike an older mechanical mouse, the optical mouse can work on virtually any surface.
98
Optical mouse function
A red LED is used in the base of the mouse and the red light is bounced off
the 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.
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Benefits of an optical mouse over a mechanical mouse
Benefits 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.
Most optical mice use Bluetooth connectivity rather than using a USB wired connection. While this makes the mouse more versatile, a wired mouse has the following advantages:
» 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).
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2D scanners
These types of scanner are the most common form and are generally used to input hard copy (paper) documents. The image is converted into an electronic form that can be stored in a computer.
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A number of stages occur when scanning a document:
Computers equipped with optical character recognition (OCR) software allow the scanned text from the document to be converted into a text file format. This means the scanned image can now be edited and manipulated by importing it into a word processor.
If the original document was a photograph or image, then the scanned image forms an image file such as JPEG.
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3D scanners
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.
The scanned images can be used in computer aided design (CAD) or, more recently, sent to a 3D printer (see Section 3.2.2) to produce a working model of the scanned image.
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Technologies in 3d scanners
There are numerous technologies used in 3D scanners – lasers, magnetic resonance, white light, and so on. It is beyond the scope of this book to look at these in any great depth; however, the second application that follows describes the technology behind one form of 3D scanning.
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Application of 2D scanners at an airport
2D scanners are used at airports to read passports. They make use of OCR technology to produce digital images which represent the passport pages. Because of the OCR technology, these digital images can be manipulated in a number of ways.
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The face in Figure 3.30 shows several of the positions used by the face recognition software. Each position is checked when the software tries to compare two facial images. Data, such as:
» distance between the eyes » width of the nose
» shape of the cheek bones » length of the jaw line
» shape of the eyebrows,
are all used to uniquely identify a given face
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Application of 3D scanning – computed tomographic (CT) scanners
Computed tomographic (CT) scanners are used to create a 3D image of a solid object. 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.
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Touch screens
Touch screens
solid object
solid object now shown as a series of ‘slices’ – each
‘slice’ is stored as a digital image in the computer
Touch screens are now a very common form of input device. They allow simple touch selection from a menu to launch an application (app). Touch screens allow the user to carry out the same functions as they would with a pointing device, such as a mouse. There are three common types of touch screen technologies currently being used by mobile phone and tablet manufacturers. Similar technologies are used in other touch screen applications (for example, food selection at a fast food restaurant):
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Selection at a fast food restaurant
election at a fast food restaurant):
» capacitive
» infrared
» resistive (most common method at the moment).
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Capacitive touch screens
Capacitive touch screens are composed of a layer of glass (protective layer),
a transparent electrode (conductive) layer and a glass substrate (see Figure 3.32). Since human skin is a conductor of electricity, when bare fingers (or a special stylus) touch the screen, the electrostatic field of the conductive layer is
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3.2 Input and output devices
changed. The installed microcontroller is able to calculate where this change took place and hence determine the coordinates of the point of touching.
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There are presently two main types of capacitive touch screens:
» surface
» projective.
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With surface capacitive screens,
sensors are placed at the corners of a screen. Small voltages are also applied at the corners of the screen creating an electric field. A finger touching the screen surface will draw current from each corner reducing the capacitance. A microcontroller measures the decrease in capacitance and hence determines the point where the finger touched the screen. This system only works with a bare finger or stylus.
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Projective capacitive screens
work slightly differently to surface capacitive screens. The transparent conductive layer is now in the form of an X-Y matrix pattern. This creates a three dimensional (3D) electrostatic field. When a
finger touches the screen, it disturbs the 3D electrostatic field allowing a microcontroller to determine the coordinates of the point of contact. This system works with bare fingers, stylus and thin surgical or cotton gloves. It also allows multi-touch facility (for example, pinching or sliding).
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Advantages compared to the other two technologies
» Better image clarity than resistive screens, especially in strong sunlight » Very durable screens that have high scratch resistance
» Projective capacitive screens allow multi-touch.
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Disadvantages compared to the other two technologies
» Surface capacitive screens only work with bare fingers or a special stylus
» They are sensitive to electromagnetic radiation (such as magnetic fields or
microwaves).
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Infrared touch screens
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 (for example, with a finger touching the screen), the infrared radiation reaching the sensors is reduced. The sensor readings are sent to a microcontroller that calculates where the screen was touched:
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Infrared touch screens
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 (for example, with a finger touching the screen), the infrared radiation reaching the sensors is reduced. The sensor readings are sent to a microcontroller that calculates where the screen was touched:
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The sensors detect the infrared radiation.
If any of the infrared beams are broken (for example, with a finger touching the screen), the infrared radiation reaching the sensors is reduced. The sensor readings are sent to a microcontroller that calculates where the screen was touched:
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Advantages compared to the other two technologies
» Allows multi-touch facilities
» Has good screen durability
» The operability isn’t affected by a scratched or cracked screen.
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Advantages compared to the other two technologies
» Allows multi-touch facilities
» Has good screen durability
» The operability isn’t affected by a scratched or cracked screen.
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Disadvantages compared to the other two technologies
» The screen can be sensitive to water or moisture
» It is possible for accidental activation to take place if the infrared beams are
disturbed in some way
» Sometimes sensitive to light interference.
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Resistive touch screens
Resistive touch screens
are made up of two layers of electrically resistive material with a voltage applied across them. The upper layer is made of flexible polyethylene (a type of polymer) with a resistive coating on one side (see
Figure 3.35). The bottom layer is made of glass also with a resistive coating (usually indium tin oxide) on one side. These two layers are separated by air or an inert gas (such as argon). When the top polyethylene surface is touched, the two layers make contact. Since both layers are coated in a resistive material a circuit is now completed which results in a flow of electricity. The point of contact is detected where there was a change in voltage.
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Advantages compared to the other two technologies
Resistive touch screen
» Good resistance to dust and water
» Can be used with bare fingers, stylus and gloved hand.
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Disadvantages compared to the other two technologies
» Low touch sensitivity (sometimes have to press down harder) » Doesn’t support multi-touch facility
» Poor visibility in strong sunlight
» Vulnerable to scratches on the screen (made of polymer).
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Actuators
Output devices
When a computer is used to control devices, such as a conveyer belt or a valve, it is usually necessary to use an actuator to, for example, start/stop the conveyer belt or open/close the valve. An actuator is a mechanical or electromechanical device such as a relay, solenoid or motor. We will consider a solenoid as the example; this converts an electrical signal into a magnetic field producing linear motion: If a plunger (for example, a magnetised metal bar) is placed inside the coil, it will move when a current is applied to the coil (see Figure 3.36). This would allow the solenoid to operate a valve or a switch, for example. There are also examples of rotary solenoids where a cylindrical coil is used. In this case, when a current is supplied to the coil, it would cause a rotational movement of the plunge
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Light projectors
Projectors are used to project computer output onto larger screens or even onto interactive whiteboards. They are often used in presentations and in multimedia applications. The next section compares the basic operation of the two projector technologies.
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There are two common types of light projector:
» digital light projector (DLP)
» liquid crystal display (LCD) projector.
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Digital light projectors (DLP)
The use of millions of micro mirrors on a small digital micromirror device (DMD chip) is the key to how these devices work .
The number of micro mirrors and the way they are arranged on the DMD chip determines the resolution of the digital image. When the micro mirrors tilt towards the light source, they are ON. When the micro mirrors tilt away from the light source, they are OFF. This creates a light or dark pixel on the projection screen. The micro mirrors can switch on or off several thousand times a second creating various grey shades – typically 1024 grey shades can be produced (for example, if the mirror switches on more often than it switches off, it will produce a lighter shade of grey). This is known as a greyscale image.
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.
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Liquid crystal display (LCD) projector
These are older technology than DLP. Essentially a high-intensity beam of light passes through an LCD display and then onto a screen. How this works in principle is described below:
» a powerful beam of white light is generated from a bulb or LED inside the projector body
» this beam of light is then sent to a group of chromatic-coated mirrors (known as dichromic mirrors); these reflect the light back at different wavelengths
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Advantages of DLP projectors
higher contrast ratios
higher reliability/longevity
quieter running than LCD projector
Uses a single DMD chip which means no issues lining up the images
Smaller and lighter than LCD projector
They are better suited to dusty or smoky atmosphere
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Disadvantage of DLP projectors
image tends to suffer from ‘shadows’ when showing a moving image
DLP do not have grey components in the image
the colour definition is frequently not as good as LCD projectors because the colour saturation is not as good (colour saturation is the intensity of a colour)
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Disadvantages of a lcd projector
although improving, the contrast ratios are not as good as DLPs
LCD projectors have a limited life (that is, the longevity is not as good as DLPs)
since LCD panels are organic in nature, they tend to degrade with time (screens turn yellow and the colours are subsequently degraded over time)
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Advantages of LCD projectors
give a sharper image than DLP projectors
have better colour saturation than DLP projectors
more efficient in their use of energy than DLP technology – consequently they generate less heat
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Inkjet printers
Inkjet printers are essentially made up of:
» a print head, which consists of nozzles that spray droplets of ink onto the paper to form characters
» an ink cartridge or cartridges; either one cartridge for each colour (blue, yellow and magenta) and a black cartridge or one single cartridge containing all three colours + black (Note: some systems use six colours)
» a stepper motor and belt, which moves the print head assembly across the page from side to side
» a paper feed, which automatically feeds the printer with pages as they are required.
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Thermal bubble
– 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.
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Piezoelectric
– 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.
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Laser printers
Laser printers use dry powder ink rather than liquid ink and make use of the properties of static electricity to produce the text and images. Unlike inkjet printers, laser printers print the whole page in one go. Colour laser printers use 4 toner cartridges – blue, cyan, magenta and black. Although the actual technology is different to monochrome printers, the printing method is similar but coloured dots are used to build up the text and images.
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Inkjet printer
– inkjet printers are often 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.
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Laser printer
– these devices produce high quality printouts and are very fast when making multiple copies of a document; any application that needs high volume printing (in colour or monochrome) would choose the laser printer
(for example, producing a large number of high-quality flyers or posters
for advertising). Laser printers have two advantages: they have large toner cartridges and large paper trays (often holding more than a ream of paper).
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3D printers
3D printers are used to produce solid objects that actually work. They are primarily based on inkjet and laser printer technology. The solid object is built up layer by layer using materials such as: powdered resin, powdered metal, paper or ceramic.
The alloy wheel in Figure 3.42 was made using an industrial 3D printer. It was made from many layers (0.1 mm thick) of powdered metal using a
technology known as binder 3D printing.
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The following information describes some of the features of 3D printing:
» Various types of 3D printers exist; they range from the size of a microwave oven up to the size of a small car.
» 3D printers use additive manufacturing (i.e. the object is built up layer by layer); this is in sharp contrast to the more traditional method of subtractive manufacturing (i.e. removal of material to make the object). For example, making a statue using a 3D printer would involve building it up layer by layer using powdered stone until the final object was formed. The subtractive method would involve carving the statue out of solid stone (i.e. removing the stone not required) until the final item was produced. Similarly, CNC machining removes metal to form an object; 3D printing would produce the same item by building up the object from layers of powdered metal.
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Direct 3D printing
uses inkjet technology; a print head can move left to right as in a normal printer. However, the print head can also move up and down to build up the layers of an object
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Binder 3D printing i
s similar to direct 3D printing. However, this method uses two passes for each of the layers; the first pass sprays dry powder and then on the second pass a binder (a type of glue) is sprayed to form a solid layer.
» Newer technologies are using lasers and UV light to harden liquid polymers; this further increases the diversity of products which can be made.
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Uses of 3D printing
3D printing is regarded as being possibly the next ‘industrial revolution’ since it will change the manufacturing methods in many industries. The following list is just a glimpse into what we know can be made using these printers; in the years that follow, this list will probably fill an entire book:
» the covering of prosthetic limbs can be made to exactly fit the limb
» making items to allow precision reconstructive surgery (e.g. facial reconstruction
following an accident); the parts made by this technique are more precise in their
design since they can be made from exact scanning of the skull
» in aerospace, manufacturers are looking at making wings and other parts
using 3D technology; the bonus will be lightweight precision parts
» fashion and art – 3D printing allows new creative ideas to be developed
» making parts for items no longer in production e.g. suspension parts for a
vintage car.
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LED screens
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.
This type of screen tends to be used for large outdoor displays due to the brilliance of the colours produced. Recent advancements in LED technology have led to the introduction of OLED (organic LED) screens (see later)
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LCD screens
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. How this works is outside the scope of this book. But the important thing to realise is that for LCD screens to work, they require some form of backlighting.
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Organic light emitting diodes (OLED)
Newer LED technology is making use of organic light emitting diodes (OLEDs). These use organic materials (made up of carbon compounds) to create semi- conductors that are very flexible. 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. This allows for very thin screens. It also means that there is no longer a need to use LCD technology, since OLED is a self-contained system.
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Advantages of using OLED compared to existing LEDs and LCDs:
» The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystal structures used in LEDs or LCDs.
» The light-emitting layers of an OLED are lighter; OLED layers can be made from plastic rather than the glass as used in LED and LCD screens.
» OLEDs give a brighter light than LEDs.
» OLEDsdonotrequirebacklightinglikeLCDscreens–OLEDsgeneratetheirownlight.
» Since OLEDs require no backlighting, they use much less power than LCD
screens (most of the LCD power is used to do the backlighting); this is very
important in battery-operated devices such as mobile phones.
» Since OLEDs are essentially plastics, they can be made into large, thin sheets
(this means they could be used on large advertising boards in airports,
subways, and so on).
» OLEDs have a very large field of view, about 170degrees, which makes them
ideal for use in television sets and for advertising screens.
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Loudspeakers
are output devices that produce sound. When connected to a computer system, digitised sound stored on a file needs to be converted into sound as follows:
» The digital data is first passed through a digital to analogue converter (DAC) where it is changed into an electric current.
» This is then passed through an amplifier (since the current generated by the DAC will be very small); this creates a current large enough to drive a loudspeaker.
» This electric current is then fed to a loudspeaker where it is converted into sound.
The following schematic shows how this is done:
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f the sound is stored in a computer file, it must pass through a
digital to analogue converter (DAC) to convert binary (digital) data into an analogue form (electric current) that can then drive the loudspeaker. Figure 3.47 shows how the loudspeaker converts the electric current into sound: 109
3 Hardware
» When an electric current flows through the coil of wire that is wrapped around an iron core, the core becomes a temporary electromagnet; a permanent magnet is also positioned very close to this electromagnet.
» As the electric current through the coil of wire varies, the induced magnetic field in the iron core also varies. This causes the iron core to be attracted towards the permanent magnet and as the current varies this will cause the iron core to vibrate.
» Since the iron core is attached to a cone (made of paper or thin synthetic material), this causes the cone to vibrate, producing sound waves.
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Sensors
are input devices which read or measure physical properties from
their surroundings. Examples include temperature, pressure, acidity level and length (there are many others). Real data is analogue in nature; this means it is constantly changing and doesn’t have a single discrete value. Therefore, analogue data needs some form of interpretation by the user, for example, the temperature measurement on a mercury thermometer requires the user to look at the height of the mercury column and use their best judgement (by looking at the scale) to find the temperature. There are an infinite number of values depending on how precisely the height of the mercury column is measured.
