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A project log for OSUG: Open-Source Underwater Glider

A versatile autonomous environmental drone using a buoyancy engine

alexwalexw 04/26/2017 at 15:160 Comments

I am now at a stage where I can start to think about the PCB/control board, and I shall use this project log to outline each major component and its reasoning.

For the central microcontroller, I intend to use an Atmel Atmega microprocessor as it can easily be programmed with the Arduino IDE. The design of the control board should also be straightforward, as there are many tutorials on producing a barebones board. As I do not require many inputs/outputs, I have decided upon the Atmega328P (specifically the MLF package for its small footprint, which is smaller than its through-hole/TQFP counterparts).

With regards to the gyroscope, I plan to use an IMU (inertial measurement unit) which will provide the glider with an accelerometer and magnometer, allowing for inertial navigation later on without the requirement of designing new hardware. I selected the LSM9DS1 after looking on the Sparkfun website, and I will now make use of the schematic diagrams they provide for their breakout boards; these will allow me to check my circuit against theirs to produce a board that I am sure will function. Additionally, the LSM9DS1 is an LGA package, so has a very small footprint (3.5x3mm – should be fun to solder).

There are some components which will require a 3.3v CMOS supply, so the control board will use an LM1117 voltage regulator for the supply from the batteries. To control the stepper motors, I will be using the A4988 drivers as they are readily available and feature in many tutorials with hookup guides and programming examples.

As I hope that the glider will be capable of waypoint navigation at some point, I will also provide pins to connect a GPS module. I found this suitable product from SparkFun at an affordable price. A tutorial for this particular module can be found here.

After looking in the Eagle libraries, I realise I will have to create a footprint for the LSM9DS1, but the other components are relatively standard and have footprints available. I should have a schematic for the board produced within a couple of weeks or so.

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