1. May07 – 17 SOAP: SCUBA Oxygen Analysis Project Team Members: Michael Beckman Adam Petty Rory Lonergan Jeffrey Schmidt Advisor: Dr. Gary Tuttle Client: Dan Stieler Date Presented: 04-10-2007

2. Presentation outline  Introduction and project overview  Project design  Implementation and testing  Resources and schedules  Closing remarks  Questions and answers  Demonstration

3. 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 ppO 2. PO2 is used in the diving community for simplicity.  SCUBA - Acronym for self contained underwater breathing apparatus.

4. 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.

5. Introduction and project overview

6. 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)

7.  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 (2/4)

8. Problem statement (3/4)  The needed maximum operating depth calculations are complex  Tables are commonly used, but can be easily misread

9. 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

10. 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.

11. Problem solution (2/2)

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. Project design

19. Present accomplishments  Purchased components  Completed design  Built a working oxygen analyzer  Started product testing

20. Approaches considered  Computer based Pros Pros More extensibleMore extensible Cons Cons Not as portableNot as portable  Portable device Pros Pros Small, easier to carrySmall, easier to carry Simpler more reliable designSimpler more reliable design Cons Cons Fewer expansion optionsFewer expansion options

21. Project definition activities  Client meetings  Discussions with divers  Market research

22. 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.

23. Overall system design

24. Design activities: Flow restrictor and O 2 sensor  A restricting orifice is needed to obtain a flow rate of 1-2 liters per minute  The sensor uses a chemical reaction to produce a voltage based on the percentage of O 2 present Flow restrictor diagram Oxygen sensors

25. Design activities: Amplifier  Used to increase the voltage signal from the oxygen sensor to something usable for the microcontroller's ADC The amplifier

26. Design activities: Microcontroller  The microcontroller will perform the following functions: Using its ADC to turn the oxygen sensor’s input into a digital value Using its ADC to turn the oxygen sensor’s input into a digital value Calculating the percentage of oxygen and the MOD Calculating the percentage of oxygen and the MOD Outputting the percentage of oxygen and MOD to the LCD screen Outputting the percentage of oxygen and MOD to the LCD screen PIC18F4520 microcontroller

27. Design activities: 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 Serial enabled LCD backpack

28. 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

29. 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

30. 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

31. Design activities: End-product design Current end-product design  Aluminum Enclosure  8” x 4” x 1.5”  Weighs about 1 pound

32. Implementation and testing

33. Implementation activities  Programmed microcontroller  Soldered components onto protoboard  Altered enclosure to fit the product  Put protoboard and components in enclosure  Sensor integration

34. Testing activities  Microcontroller: Function testing Function testing Boundary testing Boundary testing Low battery testing Low battery testing  Sensor: Linear output over full range Linear output over full range Accurate within 1% of full scale Accurate within 1% of full scale

35. Resources and schedules

36. Resources: Personnel

37. Resources: Financial requirements

38. Resources: Other

39. Project schedule

40. Deliverable schedule

41. Closing remarks

42. Project evaluation MilestonesRelative ImportanceEvaluation ScoreResultant Score Problem Definition10%100%10% Research15%100%15% Technology Selection5%100%5% End-product design15%80%12% Prototype implementation15%90%13.5% End-product testing10%80%8% End-product documentation5%90%4.5% Project reviews5%100%5% Project reporting10%75%7.5% End-product demonstration10%100%10% Total 100% 90.5%

43. 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

44. Recommendations for future work  Testing with additional sensors  Testing device functionality under environmental extremes  Improve battery accessibility  Add metric measurements

45. 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.

46. Unanticipated risks encountered  Part failure: Oxygen sensor, microcontrollers, amplifiers Using extreme care with parts Using extreme care with parts Ordering extra parts when feasible Ordering extra parts when feasible  Incorrect part order: Potentiometer, microcontroller Ordered several alternatives of each component Ordered several alternatives of each component

47. Closing summary  A mobile oxygen analyzer capable of displaying maximum operating depth

48. Questions?