Recently, I fabricated a crude prototype of the buoy’s sensor circuit board using perfboard and soldering connections to wire the inertial measurement unit (IMU), GPS , RGB LEDs, and Xbee to the Ndogo microcontroller. All the connections have been tested and the individual modules all function correctly so the next step is to write code for the microcontroller that will pull data from each of sensors in a specific sequence and time interval before transmitting the data to a base station wirelessly. For preliminary testing the base station will be my laptop but the concept can easily be scaled for longer ranges.
Picked up a new spool of clean PLA and am trying to reprint the upper portion of the hemisphere again. Last time I tried this print the Printrbot jammed after finishing 70% of the build.
update: link to CAD files
Finished printing the latest hull design This had to be printed in three sections due to issues with excessive overhang at the bottom portion of the hull, and is held together using M3 stainless steel cap screws. There is a hole in the center of the bottom section so an analog temperature sensor can be installed and potted.
Having replaced the large Arduino Mega with the new Sodaq Ndogo, there was now plenty of room inside the buoy to include all the extra sensors (yet another excuse to spend hours with CAD). Also, after researching static o-ring seals I have decided to test the spherical buoy design once more and integrate a 3/16″ thick gland into the lower portion of the buoy hull. The project will also use RTV as a backup to the o-ring in case the PLA is not stiff enough to properly compress the o-ring. Below is an exploded view of the new assembly.
Somewhere along the way, I spent a several weeks designing and redesigning alternative buoy shapes in CAD. I started at version V03 and ended up working my way to version V10, but I always came across the same issues…limited space inside the buoy meant I had to limit the number of onboard sensors. I had initially planned to use an Arduino Due as the brains of the project since it had a faster clock speed and larger memory compared to the standard Uno board. I also liked the idea that the Due ran at 3.3V for low power consumption which would translate to longer battery life for greater deployment times. However I could not get the Due to work with I2C when connected to my IMU so I gave up and decided to use an older Mega 2560 I had lying around which seemed to work.