May07 – 17May07 – 17SSOAP: OAP: SCUBA Oxygen SCUBA Oxygen

AnalAnalysis Projectysis Project

Team Members:Team Members:Michael BeckmanMichael Beckman

Adam PettyAdam PettyRory LonerganRory LonerganJeffrey SchmidtJeffrey Schmidt

Advisor:Advisor:Dr. Gary TuttleDr. Gary Tuttle

Client:Client:Dan StielerDan Stieler

Date Presented: 04-25-2007Date Presented: 04-25-2007

Presentation outlinePresentation outline

Introduction and project overviewIntroduction and project overview Project design Project design Implementation and testingImplementation and testing Resources and schedulesResources and schedules Closing remarksClosing remarks Questions and answersQuestions and answers DemonstrationDemonstration

Definitions and acronymsDefinitions and acronyms Atmospheric pressure (ATM) Atmospheric pressure (ATM) - A measurement of pressure with 1 ATM - A measurement of pressure with 1 ATM

being the pressure at sea level. being the pressure at sea level.

Central nervous system (CNS) Central nervous system (CNS) -- Refers to the brain and spinal cord.Refers to the brain and spinal cord.

Maximum operating depth (MOD)Maximum operating depth (MOD) - A SCUBA diving term referring to the - A SCUBA diving term referring to the maximum safe depth based on the partial pressure of oxygen. While opinions maximum safe depth based on the partial pressure of oxygen. While opinions vary, the accepted safe maximum PO2 is 1.4 ATMs, with an absolute limit of vary, the accepted safe maximum PO2 is 1.4 ATMs, with an absolute limit of 1.6 ATMs.1.6 ATMs.

NitroxNitrox - A gas mixture comprised of nitrogen, oxygen and other trace gases. - A gas mixture comprised of nitrogen, oxygen and other trace gases. In SCUBA diving, Nitrox is commonly mixed to contain a higher than normal In SCUBA diving, Nitrox is commonly mixed to contain a higher than normal percent of oxygen (greater than 20.9%).percent of oxygen (greater than 20.9%).

Oxygen sensorOxygen sensor - A device that measures the percentage of oxygen in a - A device that measures the percentage of oxygen in a gaseous medium using a chemical element.gaseous medium using a chemical element.

PO2PO2 - Partial pressure of oxygen, more accurately termed ppO - Partial pressure of oxygen, more accurately termed ppO22. PO2 is used . PO2 is used in the diving community for simplicity.in the diving community for simplicity.

SCUBA SCUBA - Acronym for self contained underwater breathing apparatus.- Acronym for self contained underwater breathing apparatus.

AcknowledgementsAcknowledgements The team would like to thank their client, Dan The team would like to thank their client, Dan

Stieler, for proposing this project. He provided a Stieler, for proposing this project. He provided a great deal of insight into oxygen sensors and great deal of insight into oxygen sensors and analyzers and gave the team some great ideas analyzers and gave the team some great ideas about how to design the device.about how to design the device.

The team would like to thank the SSOL lab for The team would like to thank the SSOL lab for allowing the team to use their facilities and allowing the team to use their facilities and equipment.equipment.

Introduction and Introduction and project overviewproject overview

Problem statement (1/4)Problem statement (1/4) As a diver descends, pressure increases As a diver descends, pressure increases

and more gas dissolves in the body and more gas dissolves in the body (Henry’s Law)(Henry’s Law)

As depth increases, more nitrogen As depth increases, more nitrogen dissolves in the blood stream which must dissolves in the blood stream which must be “off gassed” slowly on the way back to be “off gassed” slowly on the way back to the surfacethe surface

Failure to do so may cause Failure to do so may cause decompression sickness (the bends)decompression sickness (the bends)

Partial pressure of oxygen limits dive Partial pressure of oxygen limits dive depth and timedepth and time

Central nervous system (CNS) oxygen Central nervous system (CNS) oxygen toxicitytoxicity

Maximum PO2 of 1.4/1.6 ATMsMaximum PO2 of 1.4/1.6 ATMs

Problem statement (2/4)Problem statement (2/4)

Problem statement (3/4)Problem statement (3/4)

The needed maximum operating depth The needed maximum operating depth calculations are complexcalculations are complex

Tables are commonly used, but can be Tables are commonly used, but can be easily misreadeasily misread

Problem statement (4/4)Problem statement (4/4)

Goal:Goal:

Create a device to analyze and output the Create a device to analyze and output the percentage of oxygen in a SCUBA tank percentage of oxygen in a SCUBA tank while simultaneously outputting the while simultaneously outputting the maximum operating depthmaximum operating depth

Problem solution (1/2)Problem solution (1/2)

Build a mobile oxygen analyzer that uses an Build a mobile oxygen analyzer that uses an oxygen sensor.oxygen sensor.

This device takes the oxygen content of a This device takes the oxygen content of a SCUBA tank as input and outputs the oxygen SCUBA tank as input and outputs the oxygen percentage onto an LCD screen, along with the percentage onto an LCD screen, along with the MOD for the mixture. MOD for the mixture.

Problem solution (2/2)Problem solution (2/2)

Operating environmentOperating environment

Since the device is used to analyze tanks both Since the device is used to analyze tanks both indoors and outdoors, it was made to be water indoors and outdoors, it was made to be water resistantresistant and to operate in a wide range of and to operate in a wide range of climates.climates.

This device is not water proof.This device is not water proof. It is not guaranteed to operate correctly in It is not guaranteed to operate correctly in

temperatures above 104° F or below 32° F.temperatures above 104° F or below 32° F. It was not designed to be able to survive It was not designed to be able to survive

extreme physical trauma.extreme physical trauma.

Intended usersIntended users This device is intended to

be used by certified SCUBA divers and people that refill SCUBA tanks.

This will typically be a fully certified adult trained to handle and/or fill high pressure oxygen containers.

Intended usesIntended uses

Users can use the device to determine two Users can use the device to determine two things: things: The percentage of oxygen content in a SCUBA tank. The percentage of oxygen content in a SCUBA tank. The MOD for a SCUBA dive. The MOD for a SCUBA dive.

Users that aren’t interested in the MOD can use Users that aren’t interested in the MOD can use the device like any other conventional oxygen the device like any other conventional oxygen analyzer.analyzer.

AssumptionsAssumptions

The parts required are affordable and are The parts required are affordable and are commercially available.commercially available.

The team has access to a SCUBA tank for testing.The team has access to a SCUBA tank for testing. All of the components operate at or above their All of the components operate at or above their

specifications.specifications. The components needed to make the device are The components needed to make the device are

capable of being powered by a battery.capable of being powered by a battery. The user will follow the device’s instructions and The user will follow the device’s instructions and

not use the device in a manner that was not use the device in a manner that was unintended by the team.unintended by the team.

LimitationsLimitations The oxygen sensor must be capable of reading in oxygen The oxygen sensor must be capable of reading in oxygen

content of a SCUBA tank within 1% of the actual value.content of a SCUBA tank within 1% of the actual value. The MOD must be accurate for the full range of the The MOD must be accurate for the full range of the

possible oxygen input (0% Opossible oxygen input (0% O22 – 100% O – 100% O22).). The device’s user must have a way to correct inaccurate The device’s user must have a way to correct inaccurate

input (calibrate the device).input (calibrate the device). The device needs to display the oxygen percentage and The device needs to display the oxygen percentage and

the MOD on the LCD.the MOD on the LCD. The device needs to be mobile and battery powered.The device needs to be mobile and battery powered. The cost of the device’s parts should not greatly exceed The cost of the device’s parts should not greatly exceed

$150.$150. The oxygen sensor can only be used in temperatures The oxygen sensor can only be used in temperatures

below 104° F and above 32° F.below 104° F and above 32° F. The oxygen sensor must be stored in an environment The oxygen sensor must be stored in an environment

where the temperature is below 122° F and above 32° F.where the temperature is below 122° F and above 32° F.

End product and deliverablesEnd product and deliverables

A fully functional oxygen analyzer that is A fully functional oxygen analyzer that is capable of outputting the oxygen capable of outputting the oxygen percentage of a SCUBA tank and the percentage of a SCUBA tank and the maximum operating depth for a dive.maximum operating depth for a dive.

Project designProject design

Present accomplishmentsPresent accomplishments

Purchased componentsPurchased components Completed designCompleted design Built a working oxygen analyzerBuilt a working oxygen analyzer Finished product testingFinished product testing

Approaches consideredApproaches considered

Computer basedComputer based ProsPros

• More extensibleMore extensible ConsCons

• Not as portableNot as portable

Portable devicePortable device ProsPros

• Small, easier to carrySmall, easier to carry• Simpler more reliable designSimpler more reliable design

ConsCons• Fewer expansion optionsFewer expansion options

Project definition activitiesProject definition activities

Client meetingsClient meetings Discussions with diversDiscussions with divers

Easy to use with glovesEasy to use with gloves Easy to calibrateEasy to calibrate Low costLow cost

Market researchMarket research Features of similar itemsFeatures of similar items Prices of similar itemsPrices of similar items

Nuvair O2 Quickstick 249.99$ OMS OX-AM 359.99$ Oxycheq Expedition 299.00$ Oxycheq Expedition-X 329.00$ Teledyne AD-300 399.00$ Teledyne MD-300 530.00$

Prices of similarly featured oxygen analyzers

Research activitiesResearch activities

Microcontroller: Different microcontrollers were Microcontroller: Different microcontrollers were researched to find which one could be researched to find which one could be implemented quickest.implemented quickest. Built-in ADC preferable.Built-in ADC preferable. Didn’t have programmer board for TI microcontrollers.Didn’t have programmer board for TI microcontrollers. Confusing documentation for many microcontrollers.Confusing documentation for many microcontrollers. Good documentation and examples for Microchip Good documentation and examples for Microchip

(PIC) microcontrollers.(PIC) microcontrollers.

Instrumentation amplifiers: Researched to see if Instrumentation amplifiers: Researched to see if they could remove parasitic offsets.they could remove parasitic offsets.

Overall system designOverall system design

Design activities: Flow restrictorDesign activities: Flow restrictor

A restricting orifice is A restricting orifice is needed to obtain a flow needed to obtain a flow rate of 1-2 liters per rate of 1-2 liters per minuteminute

Constant flow rate of gas Constant flow rate of gas provides consistent provides consistent readingsreadings

Flow restrictor diagram

OxyCheq flow restrictor and sensor cap

Design activities: Oxygen SenorDesign activities: Oxygen Senor R22D from Teledyne R22D from Teledyne Uses a chemical reaction to Uses a chemical reaction to

produce a voltage based on the produce a voltage based on the percentage of Opercentage of O22 present present

Accuracy: Within 1% under Accuracy: Within 1% under nominal conditionsnominal conditions

Output: 8 – 13 mV nominalOutput: 8 – 13 mV nominal Shelf-life is 6 – 24 monthsShelf-life is 6 – 24 months Response time: 6+ secondsResponse time: 6+ seconds Operating environment Operating environment

restrictionsrestrictions

Oxygen sensors

Design activities: AmplifierDesign activities: Amplifier The amplifier is used to increase the voltage signal from The amplifier is used to increase the voltage signal from

the oxygen sensor to something usable for the the oxygen sensor to something usable for the microcontroller's ADCmicrocontroller's ADC

The amplifier

Design activities: MicrocontrollerDesign activities: Microcontroller

The microcontroller performs the The microcontroller performs the following functions:following functions: Using its ADC to turn the oxygen Using its ADC to turn the oxygen

sensor’s voltage into a digital valuesensor’s voltage into a digital value Calculating the percentage of Calculating the percentage of

oxygen and the MODoxygen and the MOD

Outputting the percentage of oxygen Outputting the percentage of oxygen and MOD to the LCD backpackand MOD to the LCD backpack

PIC18F4520 microcontroller

MOD equation

Design activities: LCD BackpackDesign activities: LCD Backpack

Receives the “output to Receives the “output to display on the LCD” data display on the LCD” data from the microcontroller’s from the microcontroller’s serial-output pin and serial-output pin and reformats it so that the LCD reformats it so that the LCD can understand itcan understand it

Bridges the gap between the Bridges the gap between the microcontroller and the LCDmicrocontroller and the LCD

Serial enabled LCD backpack

Design activities: LCD screenDesign activities: LCD screen

The LCD screen The LCD screen outputs the oxygen outputs the oxygen percentage and MOD percentage and MOD at PO2s of 1.4 and at PO2s of 1.4 and 1.6 ATMs1.6 ATMs

The screen refreshes The screen refreshes every 1.5 secondsevery 1.5 seconds Formatted output on the LCD screen

Design activities: PowerDesign activities: Power The device is powered by a 9V battery, with 5V The device is powered by a 9V battery, with 5V

being used by each component in the devicebeing used by each component in the device A voltage regulator was used to keep the voltage A voltage regulator was used to keep the voltage

going into each component at 5Vgoing into each component at 5V An on/off switch is used to power up/down the An on/off switch is used to power up/down the

devicedevice

Power switch and voltage regulation circuit

Design activities: Design activities: Low battery detectionLow battery detection

When the voltage going into all the device’s When the voltage going into all the device’s components drops below 5V, a LED lights components drops below 5V, a LED lights up to indicate that the battery is lowup to indicate that the battery is low

Low battery detection circuit

Design activities: Design activities: End-product designEnd-product design

Current end-product design

Aluminum Enclosure Aluminum Enclosure

8” x 4” x 1.5”8” x 4” x 1.5”

Weighs about 1 poundWeighs about 1 pound

Sized to be easily Sized to be easily usable when a diver usable when a diver has all his/her diving has all his/her diving gear on – specifically gear on – specifically glovesgloves

Implementation and testingImplementation and testing

Implementation activitiesImplementation activities Programmed microcontrollerProgrammed microcontroller Laid out, tested, and integrated components on Laid out, tested, and integrated components on

breadboardbreadboard

Soldered components onto protoboardSoldered components onto protoboard Altered enclosure to house the protoboard, LCD Altered enclosure to house the protoboard, LCD

screen, power switch, sensor connection port, screen, power switch, sensor connection port, etcetc

Integrated protoboard and components into the Integrated protoboard and components into the enclosureenclosure

Integrated sensor with the deviceIntegrated sensor with the device Sensor is detachable and replaceable Sensor is detachable and replaceable

Testing activities: ComponentsTesting activities: Components Microcontroller function testingMicrocontroller function testing

Within function boundsWithin function bounds At function edgesAt function edges Outside of function boundsOutside of function bounds

Low battery testingLow battery testing LCDLCD MicrocontrollerMicrocontroller LEDLED

SensorSensor Linear output over full rangeLinear output over full range Accurate within 1% of full scaleAccurate within 1% of full scale

Testing activities: Testing activities: End product (1/2)End product (1/2)

Testing procedureTesting procedure Took device to Microelectronics Research Took device to Microelectronics Research

CenterCenter Plugged into SCUBA tank with regular air Plugged into SCUBA tank with regular air

(20.9% oxygen) and calibrated device(20.9% oxygen) and calibrated device With oxygen and nitrogen tanks, used flow With oxygen and nitrogen tanks, used flow

regulators to create Nitrox with a specific regulators to create Nitrox with a specific oxygen contentoxygen content

Allowed for end-product testing at different Allowed for end-product testing at different oxygen levelsoxygen levels

Testing results:Testing results:

Issue: Device has trouble operating Issue: Device has trouble operating around 100% Oaround 100% O22 due to a design flaw. due to a design flaw.

Expected % O2 Measured % O233.1 33.335.8 36.250 50.2

Testing activities: Testing activities: End product (2/2)End product (2/2)

Percentage O2 Voltage (mV) Linear (mV)20.9 9.4 9.435.8 16 16.1014354100 44.87 44.9760766

Resources and schedulesResources and schedules

Resources: PersonnelResources: Personnel

Member Advisor Mtg Group Mtg Other TotalJeff 24 54 119 197Rory 19 58 96 173Michael 25 58 105 188Adam 25 56 111 192Total 93 226 431 750

Michael Beckman (188 hours)

Rory Lonergan (173 hours)

Jeff Schmidt (197 hours)

Adam Petty (192 hours)

Resources: Resources: Financial requirementsFinancial requirements

Parts Status Original Price Prediction ModifiedWires, Cables, Connectors Provided $10.00 $0.00ADC and Microcontroller Purchased $0.00 $11.65Pspice Simulation Software Provided $0.00 $0.00DC Power Supply Provided $0.00 $0.00Soldering Iron Provided $0.00 $0.00Multi-meter or Oscilloscope Provided $0.00 $0.00Computer Provided $0.00 $0.00Microcontroller Programmer Provided $0.00 $0.00Microcontroller Programming Software Provided $0.00 $0.00Resistors, Capacitors, Op-Amps Provided $5.00 $0.00Prototyping Boards Provided $10.00 $0.00LCD Screen Purchased $15.00 $32.90Oxygen Sensor Purchased $70.00 $70.00Enclosure Purchased $20.00 $20.00Knobs and Buttons Purchased $15.00 $15.00Batteries Provided $0.00 $0.00Poster Provided $40.00 $15.00Miscellaneous (RTV Silicone) Purchased $40.00 $5.00Total $225.00 $169.55Labor $8,536.00 $8,129.00Total With Labor $8,761.00 $8,298.55

Resources: OtherResources: Other

Requirement Status PriceDC Power Supply Provided $0.00Microcontroller Programmer Provided $0.00Soldering Iron Provided $0.00Multi-meter or Oscilloscope Provided $0.00Computer Provided $0.00Pspice Provided $0.00Microcontroller programming suite Provided $0.00Poster Purchased $15.00Miscellaneous Purchased $5.00

Project scheduleProject schedule

Deliverable scheduleDeliverable schedule

Closing remarksClosing remarks

Project evaluationProject 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% 90% 13.5%

Prototype implementation 15% 100% 15%

End-product testing 10% 90% 9%

End-product documentation 5% 90% 4.5%

Project reviews 5% 100% 5%

Project reporting 10% 95% 9.5%

End-product demonstration 10% 100% 10%

Total 100%   96.5%

CommercializationCommercialization

Estimated cost to manufacture: $160Estimated cost to manufacture: $160 Market pool is smallMarket pool is small Markup is generally around 100% Markup is generally around 100% MSRP of $300 with negotiable wholesale MSRP of $300 with negotiable wholesale

price based on quantity soldprice based on quantity sold

Recommendations Recommendations for future workfor future work

Allow use of additional sensorsAllow use of additional sensors Oxygen sensors other than R22DOxygen sensors other than R22D Sensors for other gasesSensors for other gases

Make more water proofMake more water proof Improve battery accessibilityImprove battery accessibility Add metric measurementsAdd metric measurements Testing in wider temperature rangeTesting in wider temperature range Eliminate need for LCD backpackEliminate need for LCD backpack

Lessons learnedLessons learned

Establishing a set time and location to Establishing a set time and location to consistently work on the projectconsistently work on the project

Planning ahead on parts ordersPlanning ahead on parts orders Ordering extra parts in the event of part Ordering extra parts in the event of part

failure.failure. Choosing technologies that are commonly Choosing technologies that are commonly

used and have documentation readily used and have documentation readily available.available.

Unanticipated risks encounteredUnanticipated risks encountered

Part failure: Oxygen sensor, Part failure: Oxygen sensor, microcontrollers, amplifiersmicrocontrollers, amplifiers Using extreme care with partsUsing extreme care with parts Ordering extra parts when feasibleOrdering extra parts when feasible

Incorrect part order: Potentiometer, Incorrect part order: Potentiometer, microcontrollermicrocontroller Ordered several alternatives of each Ordered several alternatives of each

componentcomponent

Closing summaryClosing summary

A mobile oxygen analyzer capable of A mobile oxygen analyzer capable of displaying maximum operating depthdisplaying maximum operating depth

Questions?Questions?