P14251: Acoustic Underwater Communications
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Detailed Design

Table of Contents

Prototyping, Engineering Analysis, Simulation

Our 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.

Material Testing

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.

Parabolic Dish Analysis

Speaker Testing

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.

Electrical Calculations

Power Calculations

Electronics Calculations

Modulation

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.

Demodulation

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

Software Information

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, Simulations

Mechanical Drawings

Cad Folder

Electrical Schematics

Revision D

Simulations

FFT Plots

Software Architecture

UML Diagram

Controller Pseudo Code

Encoder Pseudo Code

Dencoder Pseudo Code

Bill of Material (BOM)

The most up-to date bill of material.

BOM

Test Plans

Electrical Test Plans

Mechanical Test Plans

Mod and Demod Test Plans

Software Test Plans

Risk Assessment

Our most up-to-date risk analysis

Risk Analysis

Design Reviews

DDR Presentation

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