It’s spring break, and you know what that means: school projects!

Just kidding, somewhat… I had a presentation about the RC car project this past week. I covered lots of details of the design so that the professors could try and find weak points, and boy, did they ever.

One of the major weak points they found was with the accelerometer. Many projects use them to determine location on a small scale. Add in a gyro and a compass, and maybe a GPS, and you know everything about your location. But what they dont’ tell you is that it involves a lot of math. To determine distance from acceleration, you have to have the complete acceleration curve over time, and do a double integral over it. The integral can be done using just sums, but without enough readings from it, you can’t get good information.

So they suggested using rotary encoders on the axles. Not a bad idea, but that would involve finding good ones and ording them. Then they would have to be mounted, and we would probably want at least two per car, and the list goes on. We could put some Hal effect sensors by the wheels and put little magnets on the wheels and thus count revolutions. This could also work, and is slightly better than the rotary encoders, but not by much. Jokingly, one professor suggested dragging a mouse behind it, thing about ball mice.

Well, that got me thinking. Mice are essentially linear encoders. Ball mice do so by converting the linear movement into rotational movement in the encoders. Optical mice do so with small scale image processing, essentially.  They take this data and send it serially via RS232, PS/2, or USB. So, if you take the guts of an optical mouse, attach it to the bottom of the car, and you run the cord up the the microcontroller, couldn’t you fake it and thus get distance measurement directly?

So I took apart a mouse that is a USB mouse that also supports PS/2 adapters. PS/2 is a much easier protocol than USB, both in terms of electrical signals and in the protocol itself. I also found out how PS/2 is suppose to work, and hooked up an oscilloscope to test it out. I didn’t have much luck, but I have since found some code that I want to try. I just need to get to the school and try stuff out. I really wish I had an oscilloscope at home….

On that note, I saw on eBay a pre-made dev board for AVR microcontrollers that can be used as a low end oscilloscope! I thought it was amazing, but still over my budget. The guy that made that is also working on one that can measure inductors and capacitors, and be a function generator, not to mention a logic analyser. That would be amazing. Like an electronics lab in a box.

Finally, as I was on my way home from school on Friday, a girl sideswiped my car. Both of us are ok, but my car is in bad shape. Luckily she’s insured, but I still might be out of a car for a while, and it might have been totalled, so…. I might have difficulty getting to school to work on these mice anytime this week.

I don’t know if anyone noticed or not, but I’ll let you all know anyway. Some of the wordpress include files got corrupted and so things where hairy for a while. No data was lost, but I had to reinstall the files. Nothing worse than that update the other week, but it was dicey if it would work. If you where getting blank pages for a while, that’s why. It was reporting an error code 500: Internal Server error. PHP was logging parse errors, and fixing the few that I tried didn’t do anything but find another one. So I just replaced the whole thing.