Crunch time

Folks, it's now T-11 days until final demo day and we're officially starting to freak out a little. Fortunately we're not a team that will easily crack under pressure. Last week our mbed broke and we had to get a brand new one... that was fun. Today we received our 8GB microSD cards and breakout boards plus our two coin cell batteries. Last week, we got our waterproof pressure sensors. They're so cool! We're going to have to design a simple PCB for it, but I think Parth said he can help us with that tomorrow. This will give us an opportunity to try our hand at Eagle software.

MS5803-05BA - Waterproof pressure sensors

After a quick solder job, we started working with the SD card through the mbed SPI interface right away. Laura has already written some test code and we're going to test that first thing in the morning.

After much deliberation, we decided to go with a smaller, analog accelerometer and do away with the 9-DOF IMU. The way our code is written, the printed values are the number of G's in each of the three dimensions. We felt like the gyroscope and magnetometer data was not well correlated to good swimming form and that the analog accelerometer (ADXL335 from Sparkfun) as well as our waterproof pressure sensors would provide us with enough data to make qualitative sense of.

Today, I also set up the two button, two LED interface. The interface is pretty clever: there are four modes of operation. The first is capture standby and is represented by the green light. This means the paddle is ready to collect data. The second is capture mode and the green light blinks. The paddle is collecting and storing information in this mode. The third is transmit standby and is denoted by a yellow light. The paddle is ready to send information in this mode. The fourth is transmit mode in which the yellow light blinks and the paddle is sending the collected data for analysis. The first LED starts and stops capture/transmission. The second LED toggles between capture and transmit modes.

New mbed, new light, new button, new accelerometer

Aadu gave us two stackable, solderable breadboards for our chips and components. This fixes our real estate problem beautifully! We're wary of soldering things too early since we aren't completely finished land testing yet, but this will probably happen in the next two days.

I worked with Gus on Solidworks a little more and we designed a base for our electronics shield. Once we determine exactly how deep the tech will be, we will design the lid and 3d print both parts with high density polymer.

Solidworks electronic shield (base)

The lid will have a ridge that will nest between the two parallel ridges on the base allowing us to better waterproof everything. The holes are where we will screw the two shield parts and the full paddle base together. Everything will be reinforced with Silicon sealant and CorrosionX too.

Still exploring our bluetooth/wireless options. We're probably going to use an internal wireless chip to communicate to another mbed connected via USB to our laptops.

We've come a long way, but we have a long way to go. Looking forward to 11 sleepless nights.