Embedded Systems
Ning Wang
Dept of Biosysems and Agricultural Engineering
Oklahoma State University
Naiqian Zhang
Dept of Biological and Agricultural Engineering
Kansas State University
At South China Agricultural University
November, 2014
What are “embedded systems”?
An
An embedded
embedded system is a computer system with a dedicated function
within
within aa larger
larger mechanical
mechanical or
or electrical
electrical system,
system, often
often with
with real-time
real-time
computing
computing constraints.
constraints. ItIt isis embedded
embedded as
as part
part of
of aa complete
complete device
device
often including hardware and mechanical parts.
often including hardware and mechanical parts.
- Wikipedia
- Wikipedia
嵌入式系统（Embedded system），是一种「嵌入机械或电气系统内部、
嵌入式系统（Embedded system），是一种「嵌入机械或电气系统内部、
具有专属功能的计算机系统」，通常要求实时计算性能。被嵌入的系统通
具有专属功能的计算机系统」，通常要求实时计算性能。被嵌入的系统通
常是包含硬件和机械部件的完整设备。相反，通用计算机如个人计算机则
常是包含硬件和机械部件的完整设备。相反，通用计算机如个人计算机则
设计灵活，以满足广大终端用户的需求。现在常见的很多设备都采用嵌入
设计灵活，以满足广大终端用户的需求。现在常见的很多设备都采用嵌入
式系统控制。
式系统控制。
Examples: Embedded system
IMPACT
 The global embedded systems market was valued at USD 140.32 billion in
2013, expected to grow at a rate of 8.1% from 2014 to 2020, to reach USD
214.39 Billion.
 Many more embedded processors per person are used than general purpose
processors
◦ A cell phone may up to eight core processors.
◦ Value of embedded electronics in Automobiles: 25% of total cost, to rise
to 35% by 2015
◦ Embedded market is 50 times the desktop market.
 Application Domains:
◦ Automotive, Avionics, Industrial Automation, Telecommunication,
Consumer Electronics, Medical, IT hardware
 Cutting edge:
◦ Multicore processors, Network-on-Chip, System-on-chip
Embedded Systems
An Embedded System is an information processing system that is:
• application domain specific (not general purpose)
• tightly coupled to its environment
Application domains: e.g. automotive, cellphone, multimedia.
Environment: type and properties of input/output information.
Tightly coupled: The environment dictated what the system’s response
behavior must be.
Constrains:
real-time, speed, resource, power consumption, cost, efficiency
Embedded Systems
An embedded system performs computation that is subject to physical
constraints, interaction with a physical environment, and execution on a
physical (implementation) platform.
In summary, an embedded system
- Is a “special purpose” unit.
- Is a computer device which has a CPU, memory and programs that
control mainly physical devices. The program is preinstalled and may
not be changed easily.
- Has limited processing power and limited electrical power and limited
data storage.
- Has “intelligence”, thus can be configured, personalized,
“programmed”.
Schematic
Embedded Systems
Embedded systems design is not a straightforward extension of either
hardware (computer/electrical engineering) or software (computer
science) design.
They have functional requirements (expected services), and extrafunctional requirements (performance/cost, robustness).
Computer Science provides (software) functionality for Instruction Set Architectures
(ISA) which are characterized by an instruction set and an organization (program
counter, register file).
Computer/Electrical Engineering deals with logical implementation and physical
realization.
An Embedded Systems design discipline needs to combine these two approaches
from the beginning of the design.
Embedded System Engineers
“Embedded systems engineer is a relatively new job classification that
merges electrical engineering and computer science. These computer
engineers work on hardware and software designs for electronic medical
equipment, industrial and military control systems, mobile communications
devices, appliances, and remote controls. They need at least a bachelor's
degree in a relevant field, and some schools now offer certificate and
undergraduate and graduate degree programs in embedded systems
engineering.” - A job recruiting company (2014)
Skills: Strong software coding and
debugging skills, some hardware
integration knowledge, and strong
problem solving skills
As you have learned “embedded
system”, let us do some real tests!
Schematic
MP3 player – simple system
 Function: Large “flash” memory to store songs
◦ Songs (audio) stored in digital form, then compressed to a set of numbers
that are of the “MP3” format
 Processing: CPU runs program in main memory
◦ Decompresses audio and generates “raw digital audio”
◦ Gets user input from button
◦ Displays information on screen
 Input/Output: Digital-Analog converter generates audible sound
waves and sends to speaker/headphones
 Interfaces: touch screen, buttons, …
GPS Navigator – more complicated
Components
◦
◦
◦
◦
GPS Radio
GPS signal processor
Map database
Processor to control display and compute routes, locations, points of
interest
◦ Video image processor to control actual screen
 May contain several different CPUs in one package
GPS Radio
Receives data from several satellites,
converts RF to digital signals
◦ Separate for each satellite
A set of at least 24 Medium
Earth Orbit satellites that
transmit precise microwave
signals,
A GPS receiver can determine
its location, speed, direction,
and time.
Radio
receiver
circuitry
Digital signals
GPS Signal Processor
Correlates satellite signals
◦ Computes timing differences
◦ “triangulates” location
Digital
Signals
GPS data
processor
Current location in
latitude and longitude
GPS Navigator
The user interface – show location on map and provide useful other
information
GPS
signals
GPS Processor
Display
Processor
MAP database
Touch Sensor
Automobile Computers
 Engine control computer
 Advanced diagnostics
 Simplification of the manufacture
and design of cars
 Reduction of the amount of wiring
in cars
 New safety features: collision
avoidance, blind-spot detection,
back up camera,…
 New comfort and convenience
features
“It would be easy to say the modern car is a computer on wheels, but it’s more like 30
or more computers on wheels,” said Bruce Emaus, the chairman of SAE
International’s embedded software standards committee.
- NY Times
Engine Control Computer (ECU)
 Read sensors (temp, pedal position, exhaust) and control fuel injector
timing and spark timing
 Control engine fan and other actuators
 Handle the CAN (Control Area Network) that is becoming common in
cars.
•
•
Interface with climate and other passenger
controls
Provide diagnostics
Other computers in car
There are more processors in the car other than ECU
◦
◦
◦
◦
◦
◦
ABS system
Climate control
Cruise control
Radio
Dashboard
Automatic doors, lights and such
Cars also have networks for “simplified wiring” as well as automotive
control networks – CAN Bus!
Simplified Wiring
OLD
S
W
I
T
C
H
E
S
Many connecting wires
NEW
L
A
M
P
S
Switches +
signal
encoders
One wire runs all
over the vehicle
and carries power
and signal
Lamps +
signal
decoders
Automobile Networking
As multiple computing units get into cars, a networking standard is
being used
◦ CAN 2.0 is predominant
Functions:
◦
◦
◦
◦
◦
Communicate between subsystems
Reduce wires
Multiplexing standard
Network addressing
“multiple networks”
coming in the future
Design approach
Phase 1: Product specification
Phase 2: HW/SW partitioning
Phase 3: Detailed
HW/SW design
Phase 4: HW/SW
Integration
 Phase 1: Design flow of
embedded system begins
with design specifications
and constraints, including
both cost and processing
time.
Phase 5: Acceptance testing
Phase 6: Maintenance and Upgrade
http://arxiv.org/ftp/arxiv/papers/1005/1005.0931.pdf
What are “Specifications”?
“A design specification provides explicit information about the
requirements for a product and how the product is to be put together.”
- Wikipedia
Leikr GPS Watch
What are “Specifications”?
 Develop specifications (“specs”) for every component in the
embedded system.
 Specs for sensors
 Specs for controls
 Specs for computer systems (speed, memory, channels….)
 Specs of sensors, controllers, and computer many include:
◦ Desired measurement accuracy, resolution, sensitivity, linearity, dynamic
performance, consistency, reliability, etc.
◦ Environment condition: temperature, humidity, pressure, external fields
(radiation, electric, magnetic,…)
◦ Compatibility with existing instruments
◦ Cost: Closely related with the performance
◦ Durability: Life of an instrument
◦ Maintenance requirements
Sensor Specifications (datasheet)
Example 1: Infrared Temperature Sensor
Example 2: Soil Sensor (Conductivity, temperature, and moisture)
Example 3: Distance Sensor
Find Out Information on a Sensor
Telaire 7001 CO2 Sensor
Read specifications!
Questions to be answered:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Parameters to be measured
Range
Accuracy
Resolution
Time response
Output signal
Other information
Working environment
Power supply
Measurement Range:
0 to 2500 ppm when using the CABLE-CO2 and a U12 or ZW
Operating Range: 32°F to 122°F (0°C to 50°C), 0 to 95% RH,
Display Resolution: ±1 ppm
Accuracy: ±50 ppm or 5% of reading, whichever is greater
Repeatability: ±20 ppm
Temperature Dependence: ±0.1% of reading per °C or ±2 ppm per °C,
whichever is greater, referenced at 25°C.
Pressure Dependence: 0.13% of reading per mmHg (corrected via
user input for elevation)
Response Time: <60 seconds for 90% of step change
Warm-Up Time: <60 seconds at 72°F (22°C)
Calibration Interval: 12 months Full factory calibration available
Battery Type: Four AA batteries (not included)
Battery Operation: 80 hours (alkaline)
External Power Supply Specifications:
AC/DC adapter (included)
Output: 6 VDC, 500mA output.
Power Connector: Round barrel with 2.5mm ID , 5.5mm OD,
12mm long, center positive (+6 VDC), outer shell ground.
Performance Parameters
Range
◦
Input range: The limits between which input can vary.
◦
◦
Input Range = Inputmax - Inputmin
Output range: The limits between which output can vary.
◦
Output Range = Outputmax – Outputmin
Example: A load cell can measure a force within the range of 0-50kN; a
thermocouple can measure temperatures within the range of 0-100°C.
Performance Parameters
Errors
◦ Absolute error = measured value – true value
◦ Relative error = measured value  true value
true value
◦ Example: A sensor might give a resistance change of
10.2 Ω when the true change is 10.5 Ω. The error is 0.3 Ω; the relative error is 2.9%.
Performance Parameters
Accuracy
◦ An accuracy of a sensor is an indication of the possible measurement
error. A temperature sensor specified as having an accuracy of ±2C
means that the reading given by the system may lie within plus or
minus 2 C of the true value.
◦ An accuracy is often expressed as a percentage of the full range
output or full-scale deflection.
Example: A temperature sensor
Range: 0 to 200 C
Accuracy: ±5% of full-range output
Error = ±5% x 200 C = ± 10 C
Performance Parameters
Sensitivity
◦ Sensitivity indicates the change in output per unit change in input.
◦ The static sensitivity is a measure relating the change in the
output associated with a given change in a static input.
dy
K  K ( x1 )  ( ) x  x1
dx
Slope!
Example: a resistive thermometer has a sensitivity of 0.5 Ω/C.
Performance Parameters
Resolution:
◦ The smallest scale increment or the least count (least significant digit) of the
measured value.
◦ Example: Hobo Temperature Data logger Resolution U10-001: 0.1 C at 25 C
Resolution:
1/10 of a second
Image Resolution:
Resolution:
1/100 of a
second
Performance Parameters
Precision: the fineness to which an instrument can be read
repeatedly and reliably.
Accuracy vs. Precision:
Low Accuracy,
Low Precision
Low Accuracy,
High Precision
Accuracy: actual vs. True value
High Accuracy,
Low Precision
High Accuracy,
High Precision
Precision: Repeatability
Performance Parameters
Hysteresis error
◦ A sensor/transducer may give different readings between an
upscale sequential test and a downscale sequential test.
eh = (y)upscale – (y)downscale
◦ Maximum hysteresis error:
%ehmax 
ehmax
ro
100%
where r0 is the full output range.
Performance Parameters
Non-linear error
◦ Most transducers have a linear relationship between the input and the
output over the working range.
◦ An error occurs when this linear relationship can not be maintained.
Non-linearity error using: (a) end-range values, (b) best-fit straight line for all values, (c)
best-fit straight line through zero point
Performance Parameters
Repeatability
◦ Describe the sensor’s capability to give the same output for
repeated measurements of the same input value.
◦ The error resulting from the same output not being given with
repeated measurements is expressed as a percentage of the full
range output:
Output max  Output min
repeatability 
full range
Example: A transducer for the measurement of angular velocity
typically quoted as having a repeatability of ±0.01% of the full range
at a particular angular velocity.
Performance Parameters
Overall Instrument Error: Combining all known
errors
uc  e12  e22    eM2
Performance Parameters
Working conditions
◦
◦
◦
◦
Temperature range
Humidity
Dust
Climate
Maintenance
◦ Warranty
◦ Life cycle
◦ Tech support
Static and Dynamic Characteristics
A calibration applies known input values to a measurement
system to observe the system output values. The goal of
calibration process is to establish the relationship between
the input and output values.
Static Calibration:
◦ Values of the variables involved do not vary with time and space.
◦ Only magnitudes of the known input and measured output are
important.
◦ By applying a range of known input values and observing the
system output values, a direct calibration curve can be
developed for the measurement system.
Static and Dynamic Characteristics
The static calibration curve describes the static input-output relationship
for a measurement system and indicates how the output can be
interpreted by a measurement.
Static and Dynamic Characteristics
Dynamic Behavior:
◦ Response time
◦ The time which elapses
after a step input is applied
to a sensor up to the point
at which the sensor gives
output to some specified
percentage, e.g. 95%, of the
value of the input.
Specifications (datasheet)
Re-catch:
Campbell Scientific Datalloger – CR3000
Design approach
 Phase 2-4: Design and
development
 Functions by HW
 Functions by SW
 Integration
Considerations:
- Application needs
- Cost
- Speed/throughput
- User-friendliness
A considerable amount of iteration
and optimization occurs within
phases and between phases.
Phase 1: Product specification
Phase 2: HW/SW partitioning
Phase 3: Detailed
HW/SW design
Phase 4: HW/SW
Integration
Phase 5: Acceptance testing
Phase 6: Maintenance and Upgrade
http://arxiv.org/ftp/arxiv/papers/1005/1005.0931.pdf
Design approach
 Phase 5: Testing
 Calibration
 Lab/indoor testing
 Practical testing
Phase 1: Product specification
Phase 2: HW/SW partitioning
Evaluation criteria:
- Specifications
- Modifications
Phase 6: Maintenance and
Upgrade
 Plan for maintenance and
upgrade
 Tech support
Phase 3: Detailed
HW/SW design
Phase 4: HW/SW
Integration
Phase 5: Acceptance testing
Phase 6: Maintenance and Upgrade
http://arxiv.org/ftp/arxiv/papers/1005/1005.0931.pdf
Design Project
eXploration Habitat (X-Hab) 2015 Academic Innovation Challenge:
Deployable Greenhouse for food production on
long-duration exploration missions
Design tasks
 Deployable mechanism
 Architecture design
 Greenhouse controls





Environment control
Water management
Plant management
Waste management
Power system
Design an Embedded system for
greenhouse control – a class project
 Select one of the five “Greenhouse
controls” tasks.
 Phase 1: Define system specifications
and constraints
 System specifications need to be clearly
defined:
 System functions
 Performance parameters
 Goals
 Design constraints need to be clearly
identified:
 Payload (<5 kg)
 Environment (temperature, relative humidity,
ambient light…)
 Cost
 Processing speed (throughput, dynamic response)
Oral Presentation
-
Wednesday
-
Use Powerpoint
10 min/team
In Chinese
Design an Embedded system for
greenhouse control – a class project
 Phase 2-4: System design (HW & SW)
 Hardware
 microcontroller






sensors
actuators
power supply
harness
Off-the-shelf products need to be selected based on specifications.
A “Block diagram” is required.
 Software




control flow
algorithms
user interface
A “flow chart” is required.
 Integration
 possible networking
 communications
 Communications (protocols and directions) need to be shown in the “block diagram”.
Design an Embedded system for
greenhouse control – a class project
 Phase 5: Testing




sensor calibrations
system laboratory tests
system field tests
Procedures for the tests are required.
 Phase 6: Maintenance and Upgrade
sensor calibrations
 A system maintenance schedule is required (Think
about the maintenance schedule for cars.)
 Possible future system upgrading needs to be
discussed.
Oral Presentation
-
Wednesday
-
Use Powerpoint
10 min/team
In Chinese