Integrated System Build & Test
Table of Contents
Team VisionThroughout the Integrated System Build and Test Phase, Team BASE has successfully produced:
- The final prototype, consisting of 15 total parts (excluding electronics) and 3D printed out of Nylon X;
- Bluetooth capabilities fully implemented and streaming to a custom Android application;
- Final testing results for all environmental sensors (temperature, pressure and humidity); and
- A draft technical report.
The final prototype was 3D printed in the CIAS Fab Lab out of Nylon X, which has higher tensile strength than ABS. The final print consisted of 15 parts took approximately 21 hours to complete (see Figures below). The updated BOM can be found here.
The major improvement in the final prototype (Rev. 3), as compared to Rev. 2, is an improved fit that applies a slight pressure to the users' head. Moreover, the band that wraps around the back of the head sits comfortably on the users' occipital cortex, rather than resting on the back of the neck.
All electronic assemblies remained the same from Rev. 2 to 3. If time had permitted, the assemblies would have been converted to flex-rigid circuits to allow for reduced assembly time and increased robustness.
Condensed View of the Final Prototype. (A) microcontroller housing, (B) battery housing, (C) environmental unit housing, (D) PPG housing.
An Android application, using the most recent Ice Cream sandwich API is under development. At the end of Week 10, the app is able to retrieve data via BLE 4.0 from one sensor at a time and the basic user interface is developed. By the end of MSD II, all sensors will be polling as needed and displayed to the user. The figure below demonstrates the four pages that the user will be able to toggle between once the app is completed.
All test plan documentation can be found here. As of Week 10, all environmental testing and SpO2 has been completed and summaries can be found below. Accelerometer testing will be completed by the end of MSD II.
HumidityThe humidity sensor is accurate to within +/- 2%; this is within specification (ER7.2)
PressureThe pressure sensor is accurate to within +/- 2kPa; this is within specification (ER8.2).
TemperatureTemperature sensor readings are inflated by 6 degrees F due to heat transfer from the head (see Figure below); this is improved from previous measurements which had an error of 11 degrees F when the sensor was placed at the back of the head. Therefore, although still out of spec (ER6.2), the temperature measurement has been improved throughout the design process. Better manufacturing techniques and material option could further insulate the sensor and prevent heat transfer.
Temperature testing data shows an increase in 6 degrees Fahrenheit when the prototype is placed on the head
At the beginning of MSD I, we identified the SpO2 measurement to be one the most difficult metrics to achieve. An off-the-shelf sensor and and pre-existing SpO2 algorithm were obtained from Maxim to simplify the design process. Although the sensor advertised an accuracy of +/- 2%, this was for when the sensor was measuring SpO2 form the finger. We, therefore, needed to test the accuracy of the sensor when measuring behind the ear. We had two major questions that needed answered:
1. Is the sensor measuring good reflected waveforms (red and infrared)?
The figure below demonstrates a typical PPG waveform versus the signal that we were receiving when measuring from behind the ear. Although the signal intensity was smaller when measuring on the head, the signal quality did not appear to be compromised.
Expected PPG waveforms (left). Waveforms when measuring SpO2 from the fimger (middle) and waveforms when measuring SpO2 from behind the ear (right)
2. Is the SpO2 value accurate?
Twelve trials were performed in which participants were asked to sit completely still and the amount of ambient light was minimized. The volunteer also wore a finger pulse oximeter which was used as the gold standard. In total, the measured SpO2 had a 6.9% error, which is out of specification (ER9.2). The figure below demonstrates the percent error for each of the 12 trials.
Although the SpO2 sensor was unable to meet specifications, there were still many successes throughout the design process. These included:
- Developing a custom PCB for the PPG sensor which allowed for a smaller design;
- Demonstrating proof-of-concept of SpO2 measurement behind the ear; and
- Identifying limitations of measuring from behind the ear.
Recommendations for future work include:
- Housing should better occlude ambient light; and
- Use accelerometer data to determine movement and filter bad PPG data.
Risk Management & Problem TrackingWe did not need to update our Risk Management plan during this phase. Our problem tracking document can be found here. At this point, all major problems have been resolved.
Design Review Materials
Our 3 Week Plan Document can be found here.
To Be Completed by Week 14
- Three final prototypes of varying sizes (S, M, L);
- Custom Android application streaming and displaying all data to the user;
- All testing and documentation completed;
- A "visionary" model of the design, developed by our ID (Byung Kim); and
- A revised technical paper, Imagine RIT poster and Lightning talk slide submitted to the MSD office.
- Terry: Complete Android application and ensure software robustness.
- Tegan: Final sensor testing and administrative tasks (technical paper, documentation package, etc.)
- Htet: Continue soldering electrical assemblies for final prototypes.
- Andrew: Design and print various prototype sizes and document mechanical drawings.
- Alex: Complete Android application.