Integrated System Build & Test
Table of Contents
Team Vision for Integrated System Build & Test PhaseMSDII Third Phase Summary:
- Exiting the last phase our team had several open items hindering our progress towards a functioning microfluidic device. As captured in the previous phase problem tracker you will see that our main issue is getting consistent readings from our photo diode. In testing we had discovered that the diode can be extremely selective when it comes to receiving and producing a signal. We were not sure which factors of the device could be influencing the varying diode outputs. This phase would be used to work on determining the root cause of these malfunctions and understanding how we can remove their influence. The PCB design and electrical subsystems were at the point where ordering a final PCB was within the scope of this phase. Aluminum for the final chassis had been ordered and was delivered early in the phase with plans to make final design changes before machining could commence.
- With many open issues this phase saw the development of additional problems and consistent countermeasure development. To work out the issues of the photo diode and device readings we had ordered 3-Methylindole, an organic compound which fluoresces similarly to tryptophan, but emits a stronger signal given the power input. Attempting to find a device on campus to measure the fluorescence of light in the 357nm range is extremely difficult and our attempt to use such a device showed that it was not capable of working in the ultraviolet. From here we decided to attempt using our own device with the compound, but quickly learned that it can only dissolve in ethanol, which dissolves our PDMS device. With few options left we used a glass slide with our device but again found issues. When using a glass slide, sample, and plastic film to suspend the sample the LED was unable to reach the photo diode. With the remaining subsystems on track we came to the conclusion that the current photo diode is not sensitive enough to measure the low levels of emission we are creating. As the phase ends we have ordered a new photo diode with 76x the surface area for photo reception. This has certainly pushed some project steps back but for the time being we are still within the scope of feasibility.
Current Phase Gantt Chart
Test Results Summary
Vibrations - Modal Analysis
Model Analysis: Using the overall mass and stiffness of a structure model analysis is used to find the periods at which the structure will naturally resonate. NASA CubeSat requirements prohibit 1st resonance frequency to be above 100 Hz
Modeling: Assumptions: Specifics regarding internal components unknown. Shapes and sizes were estimated to serve as placeholders CubeSat launched from PicoSatellite Orbital Deployer (P-POD) P-POD is constrained along the rails (sides), but it allowed slight movement in the vertical direction. Constrained in both x and y directions and allowed slight freedom in z.
Results: Mode 1:
Mode 1: 56.271Hz
Mode 2: 152.1Hz
Mode 3: 156.3Hz
Mode 4: 157.75Hz
Mode 5: 171.79Hz
Mode 1 is significantly lower than 100 Hz. Changes to internal components should not result in drastic changes.
Snippet of the command line interface for our project
Datasheets from Google Drive link in image:
Boards for Manufacture
3-Methylindole Testing Results
Datasheets for original photodiode and new photodiode from Google Drive link in image:
Summary of MixingDifferent PDMS layer thicknesses were used as the cover for the microfluidic channel:
- 100 micrometer
- 600 micrometer
As in past iterations, the microchannel was assembled with layers of PDMS sealed with a corona wand. The cover layer was left off until testing time, where the reagent and protein were added to their respective channels, and then the cover was corona treated and applied to the top to complete the microchannel.
When the 100 micrometer cover was subjected to the solenoids, numerous leaks immediately appeared. This cover was deemed too thin for intended usage.
When the 600 micrometer cover was subjected to the solenoids, there was minimal evidence of leaking. However, there was still the issue of bubbling due to the mixing of the reagent with air that was already in the channel. There are two steps that can be taken to avoid this problem:
- Wait for the bubbles to die out before taking the spectroscopic reading.
- Seal the cover and let it cure in a vacuum chamber to remove excess air from the channel.
Due to this issue, the plan for quantification of mixing has not been executed yet.
Preliminary Backup PlansGreen Fluorescent Protein - Backup Plan A
Risk and Problem Tracking
Link to the live Risks document: Integrated System Build and Test Risks
Plans for next phaseMallory Rauch's Three Week Plan : Mallory's Goals
Anna Jensen's Three Week Plan : Anna's Goals
James Lewis's Three Week Plan : James's Goals
Darin Berrigan's Three Week Plan : Darin's Goals