Integrated System Build & Test with Customer Demo
Table of Contents
Team Vision for System Level Demo with CustomerMSDII Fourth Phase Summary:
- Entering the fourth phase our team remained in a state of limbo where we were left unsure of our project's potential for success. Ordering a drastically more sensitive photodiode and having the completed boards in hand would allow for the greatest potential of success. Meeting with our guide Mr. Paschal indicated that if testing with the new equipment failed we would no longer pursue problem solving. We would then focus solely on project summarizing and ImagineRIT prep. With only a few weeks until ImagineRIT it would not be feasible to attempt further problem mitigation.
- This phase was very successful at proving the feasibility of our project. The new photodiode is very sensitive and great at detecting varying levels of light, specifically 350nm light. We still have some issues with getting absolutely consistent testing conditions. Slight variations in ambient light can potentially alter the diode's output. Testing varying conditions with PDMS, filters, BSA, Hemoglobin, and a water solution showed that varying certain variables has a measurable effect on the diode. This is exactly the result we were hoping for. It indicates that our device is functioning properly and we will not be finishing the semester with open ended project results. The next steps are to validate the testing results and begin preparations for ImagineRIT and project handoff.
Project Testing Results
Our photodiode reading with BSA was about 2.8x higher than the reading with water. The 3-methylindole was about 3.3x higher than water. Hemoglobin did not work very well but we didn't verify the concentration. These tests were completed before the mounting hardware was printed, and we plan to rerun these tests using the mounting hardware. The following image shows the components and results of each test scenario.
Note: Voltage reading of 5 means the photodiode was flooded and an accurate result cannot be determined
The following image shows the components with detailed notes about each test scenario.
Once the mounting hardware was printed, we had time to run three tests to verify that protein would intrinsically fluoresce. The previous tests listed above did not have control tests for the reagents associated with 3-methylindole and BSA. The following tests show the control tests for BSA protein: a blank well, a well with just PBS, and a well with PBS and BSA. The well with PBS and BSA resulted in a voltage reading that was double that of the well with just PBS, which indicates that intrinsic fluorescence was detected and the setup works.
The code used to run the test is Arduino based and is here as an arduino file and a text file. This code outputted to a COM port which was read by the program 'processing.' That program can be found as a processing file and a text file.
Testing for denatured proteins
Improvements to Microfluidic Well
Improvements to the device were required as leaking continued to occur with the first iterations of the device that required only one top or bottom layer. The leaks were often caused due to poor sealing of the final layer of PDMS that was placed on top of the reagent and powder substance being studied (BSA or hemoglobin). After many pass/fail attempts, we have come to a solution to reduce or in most cases completely eliminate leaking. The new system for assembly requires an additional bottom layer of PDMS. The device is now fully assembled without the additional bottom layer. The liquid reagent is then placed into the device using a needle through the bottom layer of PDMS. All additional air is pressed out of the device using the needle as well. The bottom layer is then sealed to a second layer of PDMS that closes off the hole created by the needle prick. This design has appeared to work best and will continue to be used for the remainder of the course.
Finalized Solenoid Mounting Hardware
1U Skeletized Chassis by Pumpkin Inc. Meets required NASA standards for CubeSats as well as different launchers 5052-H32 Aluminum, Walls - 1.27mm thick, Bases - 1.5mm thick, Rated for -40 to +85 °C, 97.46mm X 97mm interior
The chassis itself is alodyned while the walls are hard anodized. This allows for the chassis to remain conductive creating a Faraday cage. If the chassis were completely hard anodized, it would become an electrical insulator. Able to easily integrate solar panels Price - $925.00. Unable to manufacture in house due to specialized material treatments. Rapid prototyping was utilized to create a mockup.
Issue encountered: LED through hole pins were accidentally sized backwards, the value that was supposed to be the drill diameter was accidentally used as the pad dimensions while the pad dimension was used as the drill diameter. I.E. a .45mm drill with a .25mm additional pad was required, the values used in the design were .25mm drill and .45mm pad.
Lesson learned: always double check the datasheet and confirm the size in PCB layout, in this case the issue was because the pad diameter was asked for first and not the drill size.
Solution: Luckily the boards were cheap and the change is simple. An updated board has been ordered to fix the issue
Issue encountered: Photodiode did not have proper output, value never changed no matter the light source. After additional testing and referencing schematic and datasheet it was determined the PCB's footprint for the photodiode was wrong.
Lesson learned: Confirm the direction of the photodiode or whatever part is being used when designing the footprint. In this case the datasheet showed the photodiode upside down and then inverted facing up, this was accidentally not accounted for during design. Always go through footprints created a second time to make sure footprint is the correct orientation.
Solution: Third unneeded (case) pin was removed from photodiode so as to be able to arrange it properly on the PCB. This allowed for the correct operation of the circuit at a loss of strength at the mounting point. A future board revision would be needed to completely repair the issue but for testing purposes what has been done is all that is required.
Risk and Problem Tracking
Link to the live Risks document: Integrated System Build and Test with Customer Demo Risks
- Current Problem Tracker