Linefollow2

Completed 26 January 2000.

This machine is much simpler than LineFollow1. It uses two light sensors and two motors. Basically, it just stops the wheel that sees black. It's simpler, faster, and smaller than LineFollow1. Much better engineering. It was also built with the intention of using it as the sound source for the Acoustic Point Source Locator, so there's an extra "singer" thread running to produce charicteristc beeps. The synthesizer on the RCX was not flexible enough for the initial stages of the project. We could probably make it work now!

I learned some things about the Lego RCX box, though, that seem obvious in retrospect. First, the light sensors are not identical. One reports different values than the other when looking at the same surface. If you read the code, I used just one threshold for both light sensors -- I found one that fit the range of both sensors. Also, the light levels reported by the sensors varies significantly with the battery level. I believe that the normal Lego software compensates for this, but I haven't looked into how to do it.

Last, the code for this project should probably have been threaded differently. I could have written a thread that monitors the left light sensor and controls the left wheel, and a thread that monitors the right light sensor and controls the right wheel. Next time I build this machine, I will work with this. :-)

The software for linefollow2 was written in C to run under the the LegOS 0.2.3. The source is provided below:

source/

I don't have any photos of this model. I'll just have to build it again!