3.1 Computers and their components

A general purpose computer makes use of input, output, primary memory and secondary storage.

• Input: Piece of hardware that is used to enter data into a computer such as keyboard, mouse, scanner, microphone
• Output: Piece of hardware that is used to display or produce the results of processed data. Eg. Speaker, Monitor, Printer
• Primary Storage: The CPU directly accesses primary storage. Some examples include RAM, ROM, Cache Memory.
• Secondary Storage: The CPU does not directly access secondary storage. Examples include HDD (Hard Disk Drive), SSD (Solid State Drive), DVD (Digital Versatile disk), Blu Ray disk. The secondary memories are all non-volatile or persistent.
• Removable Secondary Storage: Portable storage devices that can be removed and used across multiple systems. Examples are USB Flash Drives, CDs, DVDs.

Embedded System

• A combination of hardware and software designed to carry out a specific set of tasks.
• These are small computers that are often part of a more extensive system
• May contain
  • Microcontrollers - CPU, RAM, ROM and other peripherals on one single chip
  • Microprocessor - Integrated circuit with CPU only
  • System on Chips (SoC) - microprocessor with I/O ports, storage and memory
• Process
  • Input from the user is sent to the microprocessor (ADC may be required)
  • Data from the user interface is also sent to the microprocessor
  • The microprocessor then sends signals to actuators which are the output
• Applications
  • GPS systems
  • Security Systems
  • Vending Machines
  • Washing Machines
  • ATM (Automated Teller Machine)
  • Microwave

Principal operations of hardware devices

Microphone

• Used to input sound to a computer
• When a microphone picks up sound, a diaphragm vibrates
• Vibrations cause the coil to move past a magnetic core, generating electrical signal
• The signal goes to a sound card and is converted into digital values and stored in a computer
• Voice recognition: voice is detected and converted into digital

Touch screen

Laser printer

• Rotating Mirrors and a laser beam is used to project an image of the page on a photosensitive drum
• The drum converts the image into an electric charge, which attracts charged toner causing it to the image
• Electrostatic charged paper is rolled against the drum and the charge pulls toner away from drum onto paper
• Heat applied in the fuser to bond the toner on the paper
• The charge is removed from the drum and the excess toner is collected for reuse or disposal

Speaker

• Digital data passed through a DAC, to convert to physical vibrations
• The electric current in the voice coil generates an electromagnetic field
• Change in digital audio signal causes current direction to change, which changes field polarity
• Electromagnet is either attracted or repelled to a permanent magnet, causing a diaphragm that is attached to the coil to vibrate
• Vibration transmitted to air in front of the speaker
• The degree of vibration determines the amplitude and frequency of the sound wave produced

3D printer

• Uses inkjet technology; a print head can move horizontally as in a normal printer.
• However, the print head can also move vertically to build up the layers of an object.
• Uses a nozzle to squirt material onto the printer bed to create a physical layer to match the design.
• The solid object is built up layer by layer using materials such as powdered resin, powdered metal, paper, ceramic powder etc.
• The object is then cured (e.g. resin-made objects are hardened by UV)
• Applications
  • Prosthetic limbs made to exactly fit the recipient
  • Items to allow precision reconstructive surgery
  • In aerospace, manufacturers are looking at making wings and other parts using 3d technology; the bonus will be lightweight precision parts
  • In 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.

Virtual Reality Headset

• Virtual headsets consist of 2 lenses, (an LCD) display, a circuit board with sensors, a cover and foam padding
• The display provides a simulation of a 3D environment generated by a 3D graphics package
• The user can ‘move’ in the virtual environment by moving their head or using controllers
• The headset has speakers that output surround sound to give a realistic experience.
• The user's head movements are detected using a sensor (gyroscope/accelerometer)
• The data is transmitted to a microprocessor that analyses the data to identify the direction/speed of movement.
• Some headsets use digital cameras that record the user's eye movements for analysis.

Magnetic Hard Disk/Hard Disk Drive

• Have platters with surfaces covered with magnetisable material
• These platters are mounted on a central spindle and spins at high speed
• Platter’s surface is divided into concentric tracks & sectors, where data is encoded as magnetic patterns
• Data is accessed using read/write heads
• During writing: Changes in current in the head causes magnetic field variation on the disk
• During reading: Changes in magnetic field from the disk produces current variation in the read head
• Very slow data access compared to RAM

Solid State (Flash) Memory

• Are usually based on NAND gates
• Made of a grid of rows and column with 2 transistors at each intersection
• Two transistors:
  • Floating Gate: stores electrons, Where the presence or absence of charge (electrons) represents 1 or 0 respectively
  • Control Gate: Regulates charge (electrons) flow for read/write
• Benefits:
  • Data access is faster than HDD
  • More reliable
  • Considerably lighter
  • Lower power consumption
  • Run much cooler than HDDs
  • Very thin
• Drawback: questionable longevity

Optical disk Reader/Writer

• Disk surface contains a reflective metal layer and is rotated
• A tracking mechanism moves the laser assembly across the disk
• A lens focuses laser onto the disk’s surface
• The laser beam is used to read or write data
• Tracks consist of sequences of amorphous and crystalline states on the metallic layer
• During reading: The laser reflects differently off the states, encoding data as bit patterns
• During writing: The laser alters surface to different states along the track, corresponding to 1s or 0s.

Buffer

• A queue or temporary storage area used to hold data while it is being transferred from one place to another

• Cache: Short-term memory storage storing frequently accessed data

RAM and ROM

Types of RAM

Types of ROM

Control/Monitoring System

Sensors

• Input devices that measure/take (physical) readings of the surrounding environment which is converted to digital using Analogue to Digital Converter (ADC).

Monitoring System

• Designed to observe and collect data about a process or environment without influencing it
• Continuously measures variables and sends real time data to display or analyse

Control System

• Along with monitoring, these take actions to maintain or change the state of a process or system
• Event-driven system: The controller changes the system's state after some event
• Time-driven system: The controller takes action at specific point in time
• Examples: Automatic doors, heating systems, taxi meters, elevators, washing machines, domestic robots, GPS systems, traffic lights (Fixed time and dynamic control)

Feedback Systems

• System output affects the sensor’s input
• Makes sure that a system operate following the given criteria
• Enabling the system output to affect subsequent system inputs may cause a change in the actions taken by the system
• This enables the system to automatically adjust conditions in a continuous process.

Process of Monitoring/Control

• Sensors send signals to microprocessor
• Analogue signals are converted to digital (using ADC)
• Microprocessor compares value to stored value
• If value is out of range
  • Microprocessor send signal to cause an action to occur
• If value matches stored values
  • No action taken
• Output/record readings
• Monitoring is continuous

Types of Sensor:

• Acoustic/Sound

  • Act like a microphone that converts sound to electric pulses.
  • Application: Detect the noise of liquids dripping in a pipe, Pick up footsteps

• Infra-red (Active):

  • Uses an invisible infrared beam. When the beam is broken or disturbed, it changes the amount of infrared light reaching the detector.
  • Application: Detect intruders in a burglar alarm system, count people entering/leaving a building

• Infra-red (Passive):

  • Detect the heat emitted by any object
  • Application: Detect intruders in a burglar alarm system, count people entering/leaving a building

• Pressure

  • Measures the pressure applied
  • Application: Intruder alarm system, Weigh things, monitor gas pressure, automatic door opening

• Temperature

  • Measure the temperature of the environment.
  • Application: Central heating system, Control/monitor a chemical process, Greenhouse