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May07 – 17 SOAP: SCUBA Oxygen Analysis Project

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: 04-25-2007. Presentation outline. Introduction and project overview Project design

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May07 – 17 SOAP: SCUBA Oxygen Analysis Project

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  1. May07 – 17SOAP: SCUBA Oxygen Analysis Project Team Members:Michael BeckmanAdam PettyRory LonerganJeffrey Schmidt Advisor:Dr. Gary Tuttle Client:Dan Stieler Date Presented: 04-25-2007

  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 ATMs, with an absolute limit of 1.6 ATMs. • 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.

  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. 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 ATMs

  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 that uses an oxygen sensor. • This device takes the oxygen content of a SCUBA tank as input and outputs the oxygen 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 correctly in temperatures above 104° 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 typically 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. • The MOD for a SCUBA dive. • 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 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 device’s 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. • The MOD must be accurate for the full range of the possible oxygen input (0% O2 – 100% O2). • The device’s user must have a way to correct inaccurate input (calibrate the device). • 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. • The oxygen sensor can only be used in temperatures below 104° F and above 32° F. • The oxygen sensor must be stored in an environment where the temperature is below 122° F and above 32° F.

  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 • Finished product testing

  20. 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

  21. Project definition activities • Client meetings • Discussions with divers • Easy to use with gloves • Easy to calibrate • Low cost • Market research • Features of similar items • Prices of similar items Prices of similarly featured oxygen analyzers

  22. Research activities • Microcontroller: Different microcontrollers were researched to find which one could be implemented quickest. • Built-in ADC preferable. • Didn’t have programmer board for TI microcontrollers. • Confusing documentation for many microcontrollers. • Good documentation and examples for Microchip (PIC) microcontrollers. • Instrumentation amplifiers: Researched to see if they could remove parasitic offsets.

  23. Overall system design

  24. Design activities: Flow restrictor • A restricting orifice is needed to obtain a flow rate of 1-2 liters per minute • Constant flow rate of gas provides consistent readings OxyCheq flow restrictor and sensor cap Flow restrictor diagram

  25. Design activities: Oxygen Senor • R22D from Teledyne • Uses a chemical reaction to produce a voltage based on the percentage of O2 present • Accuracy: Within 1% under nominal conditions • Output: 8 – 13 mV nominal • Shelf-life is 6 – 24 months • Response time: 6+ seconds • Operating environment restrictions Oxygen sensors

  26. Design activities: Amplifier • The amplifier is used to increase the voltage signal from the oxygen sensor to something usable for the microcontroller's ADC The amplifier

  27. Design activities: Microcontroller The microcontroller performs the following functions: • Using its ADC to turn the oxygen sensor’s voltage into a digital value • Calculating the percentage of oxygen and the MOD • Outputting the percentage of oxygen and MOD to the LCD backpack PIC18F4520 microcontroller MOD equation

  28. Design activities: LCD Backpack • 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 • Bridges the gap between the microcontroller and the LCD Serial enabled LCD backpack

  29. Design activities: LCD screen • The LCD screen outputs the oxygen percentage and MOD at PO2s of 1.4 and 1.6 ATMs • The screen refreshes every 1.5 seconds Formatted output on the LCD screen

  30. 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

  31. 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

  32. Design activities: End-product design Aluminum Enclosure 8” x 4” x 1.5” Weighs about 1 pound Sized to be easily usable when a diver has all his/her diving gear on – specifically gloves Current end-product design

  33. Implementation and testing

  34. Implementation activities • Programmed microcontroller • Laid out, tested, and integrated components on breadboard • Soldered components onto protoboard • Altered enclosure to house the protoboard, LCD screen, power switch, sensor connection port, etc • Integrated protoboard and components into the enclosure • Integrated sensor with the device • Sensor is detachable and replaceable

  35. Testing activities: Components • Microcontroller function testing • Within function bounds • At function edges • Outside of function bounds • Low battery testing • LCD • Microcontroller • LED • Sensor • Linear output over full range • Accurate within 1% of full scale

  36. Testing activities: End product (1/2) • Testing procedure • Took device to Microelectronics Research Center • Plugged into SCUBA tank with regular air (20.9% oxygen) and calibrated device • With oxygen and nitrogen tanks, used flow regulators to create Nitrox with a specific oxygen content • Allowed for end-product testing at different oxygen levels

  37. Testing activities: End product (2/2) • Testing results: • Issue: Device has trouble operating around 100% O2 due to a design flaw.

  38. Resources and schedules

  39. Resources: Personnel

  40. Resources: Financial requirements

  41. Resources: Other

  42. Project schedule

  43. Deliverable schedule

  44. Closing remarks

  45. Project evaluation

  46. Commercialization • Estimated cost to manufacture: $160 • Market pool is small • Markup is generally around 100% • MSRP of $300 with negotiable wholesale price based on quantity sold

  47. Recommendations for future work • Allow use of additional sensors • Oxygen sensors other than R22D • Sensors for other gases • Make more water proof • Improve battery accessibility • Add metric measurements • Testing in wider temperature range • Eliminate need for LCD backpack

  48. Lessons learned • Establishing a set time and location to consistently work 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.

  49. 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

  50. Closing summary • A mobile oxygen analyzer capable of displaying maximum operating depth

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