The computer appears to be working electronically now. There are a few things that seem a bit wonky. The Reset/Hold/Operate switch may be a bit dirty, since it was not working reliably at first, but using it seems to be clearing it. Also, I can't get the meter to null pots when the voltage is negative, so there is something not right there that I'll have to fix.

But, it works and it computes. The circle to the left is what you get for y''=-y, where I'm plotting y in one axis and y' in the other. Since the answer to this equation is a sinusoid, you expect it to plot a circle, which it does. Interestingly, it will draw over that same circle over and over again with no apparent drift. After all these years it is rock solid. The plotter did start to have problems in one axis after a while, so I'll have to work on it.  But, the computer really does work.

It is all together other than the case, which I'm painting. I should get it installed this week. I'll look at that pot bus issue and tear back into the printer again to see why the X axis is binding up.

Back to the project

I can't believe it's been all of the way since May that I've had time to work on this project. Summer is a time of travel and projects on the house, then I had a really heavy load this fall with a lot of students, buggy software, and revisions to courses that I teach. I've just not had any time at all to work on this project. But, the semester is finally coming to a close and I am starting to have a bit more time available as I finish up projects for classes.

I've been working on two things lately. I finally got around to calibrating the quarter squared multiplier. I thought it had a problem with one section, since the bottom range was not working, but after I had finished the other sections and went back to it, it started working as I was moving pots. I think it had a dirty pot that was not making contact and I cleared it when I moved them. Anyway, it appears to be working now. I had to break the factory seals to adjust it and the adjustments were very small. It was almost in spec before I even started.

I'm also working on painting the case. I'm still debating about what to do. The original textured powder coat was pretty scratched up and was stained on top where people had put drinks and probably cigarettes (remember, this is from the 60's). I tried painting a coat on it to retain the texture, but I don't really like it. I'm debating between brown, the original color, or black, which I think would probably look nicer. I considered trying to get it repainted by someone who could duplicate the finish, but I don't really think that matters all that much, so I'm going to make it look how I like.