Quick hack to fix the slow downloads: somehow the leading 0xf1
byte of a response packet from the RCX is getting lost quite often, so I
simply make it seem that if the host gets a packet from the RCX then
that packet starts with that byte. Things are a lot faster and more reliable
now. The tarball has been updated.
Using the light sensor and a circular 2x2 plate to simulate a rotation sensor is a bit tricky, not the least because the (active) light sensor readings don't seem to vary much - 50 to 54 for me. Secondly there's the question of sampling frequency, and then relating the number of events to the quantity we're really interested in (distance or angle in the case of the turtle). Oh well, I'll see what I can do.
From the point of view of interesting programming, the turtle isn't such a great starting point. The robot is severely limited in the amount of concurrent activity it can engage in; I think one could raise or lower the pen while rotating or moving, but this is hardly useful. It seems to me that the cleverer the mechanism the more limited the concurrency possibilities.
Brown has an interesting course with some labs that help with getting started. Another way to get into interesting-program-land is to sophisticate the task.