Topic 3 - Common questions & Exam technique

“Example of embedded system”

• Microprocessor within/built into a larger system

• Performs one specific task

• Firmware not updated by user easily

• Eg. in washing machine, embedded system only controls programs for the washing cycle

“Purpose of RAM - applied”

• Stores choices

• Stores data read from sensors

“Use of ROM embedded system”

• Store data that does not change

• Data must be stored even when device is without power

• To store boot up instructions

“Explain the difference between PROM, EPROM and EEPROM”

• PROM is set once, EPROM and EEPROM can be overwritten multiple times

• EPROM needs to be removed from device EEPROM can be erased in device

• EPROM can be erased with UV light, EEPROM can be erased with voltage

• EPROM must be entirely erased before rewriting, EEPROM does not have to be entirely erased before rewriting

“Benefit of EEPROM in embedded systems”

• No additional equipment needed to change

• … enables firmware updates by non-technical users

• Can be erased and reprogrammed several times

• …so firmware can be updated

• … can erase section or whole EEPROM

• Possible to reprogram/update

• … without removing from device

“Two advantages of DRAM over SRAM”

• Lower cost per unit

• Higher bit density

• Simple design - fewer transistors

• (maybe faster access time not needed)

Differences between DRAM and SRAM

• DRAM requires to be refreshed, SRAM does not request refresh

• DRAM sores each bit as charge, SRAM uses flip-flop to store each bit

• DRAM is less expensive to manufacture, SRAM more expensive

• DRAM has slower access speeds, SRAM has faster access times

• DRAM has higher bit density, SRAM has lower

• DRAM used in main memory, SRAM used in cache

“Static RAM in laptop > DRAM”

• Faster access time

• … Does not need to be refreshed

• …used on CPU for improvement of cache speed

“Why use EEPROM in virtual headset”

• Allows frequent read/write operations

• …contents of firmware can be changed easily

• …without fully erasing contents of the firmware

“Principal operations of magnetic hard disk”

• Each hard disk has one or more platters

• Each surface of platter is capable of being magnetised

• Platters are mounted on a central spindle

• Mechanism contained in a sealed aluminium box

• Disks are rotated at high speed

• Surface has a read/write head mounted on an arm

• Surface of platter divided into sectors

• Data is encoded as a magnetic pattern for each block

• Writing: variation of current in head produces variation in magnetic field on the disk

• Reading: variation in magnetic field in the disk produces variation in current in the head

“Reasons for magnetic storage > solid state storage to store video files”

• Computer will have large number of read/write operations as it is working all the time

• Magnetic storage has more longevity

• Magnetic storage has lower cost per unit

• … videos are large files, require large amounts of storage capacity

“Describe solid state memory”

• No moving parts

• Non-volatile

• Made of arrays of NAND and NOR gates

• Controller manages components

• Transistor called floating gate

• Memory cell stores voltages that represents either 1 or 0

• Read/write is movement of electrons

“Principal operation of optical disk reader/writer

• Disk spun at high speed

• Laser shone onto disk to read/write

• …uses optical head to move into position

• Follows spiral track from center outwards

• Writing; laser bruns pits to represent data

• Reading: Laser reflects from pits and lands

• Reflection from pit and land is different

• … difference interpreted as 1 or 0

“Internal operation of laser printer”

• Revolving drum is given electrical charge

• Laser beam scans back and forth

• DIscharging certain points

• Drum is coated with oppositely charged toner

• Paper is passed through fuser to seal the image

“Laser printer use of buffer”

• Temporary storage of data

• Print instructions and data are transferred by the laptop to a buffer

• Data is retrieved from buffer to printer

• Allows user to continue using laptop at faster speed

• Without waiting for relatively slower printer

• Interrupts sent to laptop when buffer is empty/all data retrieved to request more data/stop sending data

“Principal operations of 3D printer”

• Additive manufacturing

• Uses Computer Aided Design

• Builds up model one layer at a time

• Starting from the bottom

• Using x y and z coordinates

• Material is heated and pushed through a nozzle

“VR headset internal operation”

• Uses 2 LCD displays

• Gyroscope used to determine direction of head movement

• Some use digital cameras to track eye movements”

Microprocessor

• A type of integrated circuit that…

• … is contained on a single chip

Embedded system advantages

*

• Does not require much processing power

Embedded system disadvantages

• Difficult to upgrade the firmware

Primary storage

• Directly accessed by the CPU

• Examples are RAM/ROM

Speaker

• An electric current  is sent to the speaker

• The current passes through the coil and creates an electromagnetic field

• Changes in the audio signal cause the direction of the current to change

• The electromagnet is repelled or attracted to the permanent magnet, causing the coil to vibrate

• The movement of the coil causes the diaphragm to vibrate

• The vibration creates sound waves

Resistive touchscreen

• Has  two layers

• When the user touches the screen, the circuit is completed

• A microprocessor determines the coordinates of the touch

Capacitive touchscreen

• Has several layers

• When the top layer is touched, there is a change in the electric current

• A microprocessor identifies the coordinates of the touch

“Internal operation of a microphone”

• Microphone has a diaphragm

• Incoming sound waves cause vibrations in the diaphragm

• This causes the coil to move past a magnet

• Producing an electric signal

“Internal operation of a computer” 

• Electric current is sent to the speaker

• Electric current passes through the coil

• Current in the coil creates an electromagnetic field

• Changes in the audio signal cause the direction of the electrical current to change

• This determines the polarity of the electromagnet

• The electromagnet is repelled by, or attracted to the permanent magnet

• The movement of the coil causes the diaphragm to vibrate

• The vibration causes sound waves

Difference between monitoring and control systems

Control system:

• Uses feedback

• Output of system fed back into input, affects what action takes place

• Act automatically to change environment if values out of range

• Has actuators

Monitoring system:

• No feedback

• Only stores/outputs data, output doesn’t affect operation of system

• Takes no action

• No actuators

Actuator

• Converts electrical energy into mechanical force

• eg. to open a door, turn on a fan…

Use of sensors:

• Temperature

• Pressure

• Infra-red

• Sound

Temperature: Air conditioner…

Pressure: Monitor tire pressure

Infra-red: Burgular alarm systems, TV remotes

Sound: Alarm systems, voice detection

Importance of feedback

• Ensure system operates within given criteria

• Enables system output to affect system input

• Allows conditions to be automatically adjusted

“Drawbacks of embedded systems”

• Difficult to update firmware by the user

• Errors can’t be fixed easily

• Functionality cannot be changed or extended easily

• Outdated devices often thrown away

  • Leading to e-waste

“Why a system is monitoring system”

• There is no use of feedback

• Output does not affect input of data

• System does not have any actuators