Transcript Summary Lecture - IEEE Real World Engineering Projects

Solid State Lighting for the
Developing World
(Summary Lecture)
Loren Wyard-Scott 1 *
&
Dr. James Andrew Smith 2 *
1
Dept. of Electrical & Computer Engineering
University of Alberta
Alberta, Canada
2
Institute of Sports Science
University of Jena
Jena, Germany
*
Member, IEEE
Outline
•
•
•
•
•
The Project’s Objectives
Improving the Design Process
Using Technology Closer to its Potential
Knowing the Measurement Tools
Conclusion
The Project’s Objectives
• Scenario
– A remote village of 500 people
– Limited access to light at night
– Solar charger during the day
• Objective
– Build a portable LED lamp
– Easy to recharge
– Two hours of usage
– For work & reading
Bas-Ravine, Haiti
The Project’s Objectives
• Were these goals simple to meet?
• Is your project a Success? A Failure?
Do you have enough information to answer these questions? You
are on the path to a solution, but there is still a lot of work to do!
• Many of you may have found that the objectives are
under-specified. For instance, how is charging
performed? What sort of “work” will be done with this
project as a light source?
• Designing and evaluating often requires groups to work
in “the grey”.
Improving the Design Process
•
•
Did you get lost on the way to finding a
solution – in “the grey”?
Finding a good solution to any real-world
problem requires:
1. Understanding the problem – from many
perspectives! (e.g. users, manufacturers)
2. Understanding what technology is available
(always changing!): “Product Knowledge”
3. Understanding the principles of operation of
the technologies used.
Improving the Design Process
•
•
Finding your way through any of these three
items can be challenging. It gets simpler with
experience (like this project)!
Tools and protocols that can help:
1. Correlation matrices: Understanding Design Tradeoffs
2. Multi-discipline Design Teams
3. Critical Design Review
4. Putting the Project Through its Paces: Testing
Design: Correlation Matrices
• Real design problems always have tradeoffs. “Cheap, fast, good: pick two.”
• To help understand the tradeoffs and how
they will affect the outcome is important.
• A tool that helps understand the tradeoffs
is a “Correlation Matrix”.
Design: Correlation Matrices
Longer
Brighter
Battery Life Light
Longer
Battery Life
Brighter
Light
Low Cost
Low Cost
---
--
(highly negative)
(quite negative)
--
Design:
Multi-Discipline Design Teams
• Almost every real-world project involves
more than one field of technology.
• Teams that have a wider set of
experiences and knowledge to draw from
are typically more successful.
• Commonly required skill sets: electrical,
mechanical, manufacturing, industrial
design, technical writing, financial,
resource management.
Design: Critical Design Review
• In practice it is not always possible to develop a
team that has all skill sets covered.
• A Critical Design Review (CDR) is a standard
stage of project design that can help offset this
lack.
• Once a (usually paper-based) design is
complete, the design is reviewed by people from
all walks of life, including experts.
• The feedback is used to improve the design, or,
in some cases, terminates it: “go” or “no go”.
Design: Testing
• Testing a new product is a complicated
process.
• There are discipline- and technologyspecific courses and books dedicated to
testing.
• Companies that do nothing but this aspect
of project development exist.
• Ensure that the end-user has a chance
to use a product candidate!
Using Technology Closer to its
Potential
• Understanding the options that are at your
disposal when designing is important:
“Product Knowledge” gained from reading
trade publications, journals, etc.
• Your education provides you with the tools
to understand how particular technology
works.
• Device datasheets are key to
understanding the capabilities of a device.
Technology: Datasheets
Excerpt from the datasheet for Lite-On LTL-10223W, document BNS-OD-C131/A4 by Lite-On
Electronics, Inc.
Technology: Datasheets
• This datasheet indicates that even though
the LED can handle a maximum
continuous current of only 30 mA, it can
handle 120mA for 0.1 ms every 1 ms.
• Is this relevant to our problem? Yes: it
provides a way of providing more light with
less power!
Technology: Options
We could turn on the LED very brightly with 120mA for a brief time, and take
advantage of a human’s persistence of vision to remove the flicker!
To create the time-varying voltage waveform requires some new knowledge –
but it can be done!
Technology: Options
• In resistors, electrical power is dissipated as
heat and results in a less power-efficient design.
• We could minimize this power dissipation by a
different circuit layout:
• This requires the battery voltage to be high
enough that both LEDs can be turned on.
Technology: Options
• Hopefully you found that using AA
batteries results in an operating lifetime
that far exceeds the required 2 hours.
• This indicates that there may be the
possibility of using something other than a
battery to power the LEDs: super (ultra)
capacitors!
Technology: Options
Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008.
Technology: Options
Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008.
Technology: Options
• Hopefully this has demonstrated to you
that
–Understanding what devices are available;
and
–Understanding how these devices operate
both come into play during design.
Knowing the Measurement Tools
• It is always important to understand the capabilities and
limitations of the test equipment and measurement
processes.
• Did you discover that using a CdS cell (in the manner we
have) to measure illuminosity yields, at best, an
approximate result?
– Alignment-sensitive
– Wavelength sensitive
– Temperature sensitive
• Understanding these bounds while constantly asking “is
what we are observing consistent with what we know?”
is important to any scientific process.
Conclusion
• Conventional, limited, sources of energy
are being taxed more heavily as the world
population increases.
• As a result, environmentally- and energyconscious designs are now of paramount
importance.
• The system you developed here has
taught you how some of the emerging
technologies operate.
Conclusion
• You have learned a lot about the design
process, and have hopefully enjoyed
yourselves while doing so.
• Successful completion of the project itself,
Solid State Lighting for the Developing
World, will see underprivileged peoples
provided with a safe lighting system that
can be used to expand their opportunities
by improving productivity and literacy.
For more information
• Light Up The World (LUTW)
– http://www.lutw.org/
• Hyperphysics:
– http://hyperphysics.phy-astr.gsu.edu/hbase/vision/photomcon.html
• Dr. Dr. Bill’s Optics Stuff
– http://drdrbill.com
• Super Capacitors
– http://en.wikipedia.org/wiki/Supercapacitor