Table of Contents
Prototyping, Engineering Analysis, SimulationOur team performed several empirical tests as well as simulations to verify our design. Some of these tests are still ongoing while others were finished just after the return from break.
A material test was performed to ensure the housing's durability. Per ASTM B117-11, specimens were sprayed with a salt solution for a period of at least a week. The mass of each specimen was measured before and after the test. Our results found 316 Stainless Steel to be the most resilient to this short term test.
Parabolic Dish Design
In an attempt to involve the mechanical engineers more, an attempt was made to produce a parabolic dish to amplify the signal coming into the hydrophone. The design was deemed useless if it couldn't produce a gain over 3 dB. The following spreadsheet is the of the design work put into this during the course of MSD 2. It specifically goes from in an input 3d print cost to the volume of the solid to the maximum radius and then to the gain produced from the dish.
Given the frequency ranges that our data transfer rate required, knowing that we had a speaker capable of operating in the range we needed was crucial. Using a previous team's hydrophone and ordering a speaker that we had received data sheets for we tested the operation of the speaker. We found that the speaker had functionality way beyond the spec sheet that would function for many of the modulation/demodulation schemes we might have to fall back on.
Based on preliminary testing, it was decided to move more towards an FSK modulation scheme instead of a PSK scheme. Similar to PSK, the FSK system will produce four different frequencies that each represent one of four 2 bit binary sequences.
Taking advantage of the square waves frequency properties, a band pass filter can be implemented to only obtain the center frequency value of the square wave, thus converting it to a sine wave. This will then be sent to an amplifier and then to a speaker.
Our previous chip selection for the demodulation of our QPSK scheme couldn't be made functional after reviewing data sheets and an example. This chip has been discarded and the entire demodulation scheme will be performed via digital signal processing. Specifically, an FFT will be performed using the MIT developed software, FFTW on the BeagleBone Black.
An alternative demodulation scheme via filtering is also being considered. Demodulation Through Filtering
FSK FFT Analysis
To ensure that our generated signals would be distinguishable, we performed FFT's of generated signals and plotted the results. A analysis of sampling capabilities has also been performed. Sampling Time Analysis
Based on ability to sample data, as well as our modulation and demodulation schemes, a data rate analysis was able to be completed. Data Rate Analysis
Drawings, Schematics, Flow Charts, SimulationsMechanical Drawings
Bill of Material (BOM)
The most up-to date bill of material.
Our most up-to-date risk analysis