Transcript May07 – 17 SCUBA Oxygen Analyzer

May07 – 17
SOAP: SCUBA Oxygen
Analysis Project
Team Members:
Advisor:
Michael Beckman
Adam Petty
Rory Lonergan
Jeffrey Schmidt
Dr. Gary Tuttle
Date Presented: 04-10-2007
Client:
Dan Stieler
Presentation outline
 Introduction
and project overview
 Project design
 Implementation and testing
 Resources and schedules
 Closing remarks
 Questions and answers
 Demonstration
Definitions and acronyms

Atmospheric pressure (ATM) - A measurement of pressure with 1 ATM
being the pressure at sea level.

Central nervous system (CNS) - Refers to the brain and spinal cord.

Maximum operating depth (MOD) - A SCUBA diving term referring to the
maximum safe depth based on the partial pressure of oxygen. While opinions
vary, the accepted safe maximum PO2 is 1.4, with an absolute limit of 1.6.

Nitrox - A gas mixture comprised of nitrogen, oxygen and other trace gases.
In SCUBA diving, Nitrox is commonly mixed to contain a higher than normal
percent of oxygen (greater than 20.9%).

Oxygen sensor - A device that measures the percentage of oxygen in a
gaseous medium using a chemical element.

PO2 - Partial pressure of oxygen, more accurately termed ppO2. PO2 is used
in the diving community for simplicity.

SCUBA - Acronym for self contained underwater breathing apparatus.
Acknowledgements

The team would like to thank their client, Dan
Stieler, for proposing this project. He provided a
great deal of insight into oxygen sensors and
analyzers and gave the team some great ideas
about how to design the device.

The team would like to thank the SSOL lab for
allowing the team to use their facilities and
equipment.
Introduction and
project overview
Problem statement (1/4)
 As
a diver descends, pressure increases
and more gas dissolves in the body
(Henry’s Law)
 As depth increases, more nitrogen
dissolves in the blood stream which must
be “off gassed” slowly on the way back to
the surface
 Failure to do so may cause
decompression sickness (the bends)
Problem statement (2/4)
 Partial
pressure of oxygen limits dive
depth and time
 Central
nervous system (CNS) oxygen
toxicity
 Maximum
PO2 of 1.4/1.6 ATM
Problem statement (3/4)
 The
needed maximum operating depth
calculations are complex
 Tables
are commonly used, but can be
easily misread
Problem statement (4/4)
 Goal:
Create a device to analyze and output the
percentage of oxygen in a SCUBA tank
while simultaneously outputting the
maximum operating depth
Problem solution (1/2)

Build a mobile oxygen analyzer using an
oxygen sensor connected to a device of the
team’s design.

This device takes the oxygen content of a
SCUBA tank as input and outputs that
percentage onto an LCD screen, along with the
MOD for the mixture.
Problem solution (2/2)
Operating environment

Since the device is used to analyze tanks both
indoors and outdoors, it was made to be water
resistant and to operate in a wide range of
climates.
 This device is not water proof.
 It is not guaranteed to operate in temperatures
above 120° F or below 32° F.
 It was not designed to be able to survive
extreme physical trauma.
Intended users

This device is intended to
be used by certified
SCUBA divers and people
that refill SCUBA tanks.

This will be a fully certified
adult trained to handle
and/or fill high pressure
oxygen containers.
Intended uses

Users can use the device to determine two
things: the percentage of oxygen content in a
SCUBA tank and the MOD of a SCUBA dive.

Those users that aren’t interested in the MOD
can use the device like any other conventional
oxygen analyzer.
Assumptions

The parts required are affordable and are commercially
available.

The team has access to a SCUBA tank for testing.

All of the purchased components operate at or above their
specifications.

The components needed to make the device are capable
of being powered by a battery.

The user will follow the devices’ instructions and not use
the device in a manner that was unintended by the team.
Limitations






The oxygen sensor must be capable of reading in
oxygen content of a SCUBA tank within 1% of the
actual value for the full range of oxygen input.
The MOD must be accurate for the full range of
the possible oxygen input.
The device needs to be able to correct inaccurate
input.
The device needs to display the oxygen
percentage and the MOD on the LCD.
The device needs to be mobile and battery
powered.
The cost of the device’s parts should not greatly
exceed $150.
End product and deliverables
 A fully
functional oxygen analyzer that is
capable of outputting the oxygen
percentage of a SCUBA tank and the
maximum operating depth for a dive.
Project design
Present accomplishments
 Purchased
components
 Completed design
 Built a working oxygen analyzer
 Started product testing
Approaches considered
 Computer

based
Pros
• More extensible

Cons
• Not as portable
 Portable

device
Pros
• Small, easier to carry
• Simpler more reliable design

Cons
• Fewer expansion options
Project definition activities
 Client
meetings
 Discussions
 Market
with divers
research
Research activities
 Microcontroller:
Different microcontrollers
were researched to find which one could
be implemented quickest.
 Instrumentation
amplifiers: Researched to
see if they could remove parasitic offsets.
Overall system design
Design activities:
Flow restrictor and O2 sensor

A restricting orifice is
needed to obtain a flow
rate of 1-2 liters per
minute
Flow restrictor diagram

The sensor uses a
chemical reaction to
produce a voltage based
on the percentage of O2
present
Oxygen sensors
Design activities: Amplifier

Used to increase the voltage signal from the oxygen
sensor to something usable for the microcontroller's ADC
The amplifier
Design activities:
Microcontroller

The microcontroller will perform the
following functions:
 Using its ADC to turn the oxygen
sensor’s input into a digital value
 Calculating the percentage of
oxygen and the MOD
 Outputting the percentage of oxygen
and MOD to the LCD screen
PIC18F4520
microcontroller
Design activities: LCD Backpack

Serial enabled LCD backpack
This device receives the
“output to display on the
LCD” data from the
microcontroller’s serial
output pin and reformats it
so that the LCD can
understand it
 This component bridges the
gap between the
microcontroller and the LCD
Design activities: LCD screen

The LCD screen
outputs the oxygen
percentage and MOD
at PO2s of 1.4 and
1.6 ATMs
 The screen is backlit
and refreshes every
1.5 seconds
Formatted output on
the LCD screen
Design activities: Power

The device is powered by a 9V battery, with 5V being used
by each component in the device
 A voltage regulator was used to keep the voltage going into
each component at 5V
 An on/off switch is used to power up/down the device
Power switch and voltage regulation circuit
Design activities:
Low battery detection

When the voltage going into all the device’s
components drops below 5V, a LED lights
up to indicate that the battery is low
Low battery detection circuit
Design activities:
End-product design
Current end-product design

Aluminum Enclosure

8” x 4” x 1.5”

Weighs about 1 pound
Implementation and testing
Implementation activities

Programmed microcontroller

Soldered components onto protoboard

Altered enclosure to fit the product

Put protoboard and components in enclosure

Sensor integration
Testing activities
 Microcontroller:



Function testing
Boundary testing
Low battery testing
 Sensor:


Linear output over full range
Accurate within 1% of full scale
Resources and schedules
Resources: Personnel
Michael Beckman (161 hours)
Rory Lonergan (142 hours)
Jeff Schmidt (151 hours)
Adam Petty (160 hours)
Member Advisor Mtg Group Mtg Other
Total
Jeff
20
47.1
94
161.1
Rory
17
48.1
76.5
141.6
Michael
21
48.1
82.25
151.35
Adam
21
46.1
92.5
159.6
Total
79
189.4
345.25
613.65
Resources:
Financial requirements
Parts
Wires, Cables, Connectors
ADC and Microcontroller
Pspice Simulation Software
DC Power Supply
Soldering Iron
Multi-meter or Oscilloscope
Computer
Microcontroller Programmer
Microcontroller Programming Software
Resistors, Capacitors, Op-Amps
Prototyping Boards
LCD Screen
Oxygen Sensor
Enclosure
Knobs and Buttons
Batteries
Poster
Miscellaneous (RTV Silicone)
Total
Labor
Total With Labor
Status
Provided
Purchased
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Purchased
Purchased
Purchased
Purchased
Provided
Provided
Purchased
Original Price Prediction
$10.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$5.00
$10.00
$15.00
$70.00
$20.00
$15.00
$0.00
$40.00
$40.00
$225.00
$8,536.00
$8,761.00
Modified
$0.00
$11.65
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$32.90
$70.00
$20.00
$15.00
$0.00
$15.00
$5.00
$169.55
$8,129.00
$8,298.55
Resources: Other
Requirement
DC Power Supply
Microcontroller Programmer
Soldering Iron
Multi-meter or Oscilloscope
Computer
Pspice
Microcontroller programming suite
Poster
Miscellaneous
Status
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Purchased
Purchased
Price
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$15.00
$5.00
Project schedule
Deliverable schedule
Closing remarks
Project evaluation
Milestones
Relative Importance
Evaluation Score
Resultant Score
Problem Definition
10%
100%
10%
Research
15%
100%
15%
Technology Selection
5%
100%
5%
End-product design
15%
80%
12%
Prototype implementation
15%
90%
13.5%
End-product testing
10%
80%
8%
End-product documentation
5%
90%
4.5%
Project reviews
5%
100%
5%
Project reporting
10%
75%
7.5%
End-product demonstration
10%
100%
10%
Total
100%
90.5%
Commercialization
 Estimated
cost to manufacture: $160
 Estimated market pool is small
 Markup is generally around 100%
 MSRP of $400 with negotiable wholesale
price based on quantity sold
Recommendations for
future work

Testing with additional sensors

Testing device functionality under environmental
extremes

Improve battery accessibility

Add metric measurements
Lessons learned
 Establishing
a set time and location to
consistently make progress on the project
 Planning ahead on parts orders
 Ordering extra parts in the event of part
failure.
 Choosing technologies that are commonly
used and have documentation readily
available.
Unanticipated risks encountered
 Part
failure: Oxygen sensor,
microcontrollers, amplifiers


Using extreme care with parts
Ordering extra parts when feasible
 Incorrect
part order: Potentiometer,
microcontroller

Ordered several alternatives of each
component
Closing summary
 A mobile
oxygen analyzer capable of
displaying maximum operating depth
Questions?