The biggest piece of forward progress this week was the waterproof enclosure. I tested the one I built last week and built a second one being a little bit more careful with the PVC primer and cement. I conducted the test by filling a bucket I got curious of the Society of Physics students with water and dropping the enclosure in. Not the fanciest test but it gets the job done. I did fill the enclosure with mass to make it sink and put in some scraps of a coffee filter to give a prudently indicator of moisture in the tube. I chose a coffee filter because it absorbs water well and is very clear if it is wet or not. I could of used more sophisticated methods for this but there was no reason to, I mostly just wanted to see if a lot of water was seeping in at the joints or the screw cap. The first enclosure water was not seeping in, but the second one does have a leaking problem. I believe the leak is caused by the screw cap not tightening nicely into the enclosure, I have cleaned both halves of the screw and that has not improved it. Instead of spending a lot of time trying the fix it I am just going to use the first enclosure, and call the second one a loss. This is a benefit of working with PVC, it is so cheap that not matter how you mess it up you don’t feel that you’ve really ruined anything. This coming week I am going to test a method for the enclosure that does not involve a screw cap at all.
Speaking of things not working last post I mentioned that the SD reader on prototype 3 stopped working and I spent a lot of time this week trying to figure out why. I started by teaching myself how to use a logic analyzer. A logic analyser is a tool that is attached to digital circuits, and can look at the timing and voltage across a lot of wires at once. The software can also interpret the signals going across the wire. This is really useful because it allows you to look at signals the same way the chips do. After spending a while just playing with the logic analyzer to learn it I connected it to a working SD card reader and the broken one and compared the signal in them. What I found was pretty strange in that the signals did not look anything alike. Before I saw this I assumed that the SD wasn’t working because of a wiring error, possibly some interference or crosstalk. This is not what I saw at all, I would have thought it was a software error except that I was using the same code on the same chips to control for that. This led me to the conclusion that the SD reader itself was broken and the problem did not have to do with my assembly so I ordered a new reader. Hopefully just changing out the readers work, if not I have a big problem.
Finally this week I did a lot of miscellaneous small stuff for the project and preliminary research into things we might want to do in the future. I had heard that different brands and sizes of SD cards used different amounts of power so I found a bunched and looked at them under the oscilloscope. I was not able to see any appreciable difference between them. We got a solder oven for surface mount soldering and I played with that to learn how it worked. I used the laser cutter to build a stand for prototype 3. I did this because we needed a way to hold it level for tests on the accelerometer and gyroscope. I figured out how to use our particle electron board, which is basically a fancy Arduino with cell access. I did some initial research into inductive charging (a way to charge devices wirelessly, it’s how your electric toothbrush works) so that when we build the final device we don’t have to worry about about including a charging port. And last but certainly not least I did a fair bit of work in Eagle continuing to try to consolidate all the sensors and devices onto a few small boards. Also the gyro boards I designed and ordered last week should come in soon, so I can see if I’ve actually been doing the Eagle design correctly.
While I didn’t make any huge bounds this week, and actually have taken a bit of a step back with regards to prototype 3, I feel that I am well positioned to get a lot of good work done next week.