Tuesday, August 17, 2010

ASS Part 2: Getting the screen under control.

It has been a while since I last posted about ASS. I have made a fair amount of progress, and at my current rate, with what still needs to be done, I see myself finishing this project and completing installation by the end of this week. It's a good thing too, I don't know when I'd have time to work on it during this semester.

I received my parts from sparkfun the other day. I like how the parts come in a little red box.

I hooked up the motor driver and had some fun playing around with controlling the motor. I did not hook up the screen because I had not integrated the encoder yet. I decided after some testing that my motor driver was a bit puny. I went back to sparkfun to order the next size up. I got it a couple of days ago, and hooked it up. After a few more tests I liked what I had.

Next was the encoder. After reading these tutorials:

I had the encoder pretty much locked down. After some slight modification and meshing of the code from the second tutorial I was able to produce what is currently busy to my left. I have the controller set up to move the shade up and down using the encoder as feedback. It has been running for the past 45 minutes or so, the driver chip seems to be warm but nothing too hot, and the screen stop positions haven't drifted noticeably.

Needless to say I am very proud of this auto-shade, rolling up and down. It's a bit silly, but I like watching the screen roll itself up and down.

These brief descriptions do nothing to detail how the encoder was mounted to the screen dowel. This portion of the project was especially fun for me. I had to couple the encoder to the dowel so that it could monitor the rotation and know how far the screen had lowered. I ended up using the encoder as a portion of the mounting system, just like the motor is used as a part of the mounting system. I didn't have any good shaft couplers around my house at the time, so I just grabbed the nearest thing, which was an old gear with a set screw. It fit the encoder perfectly and with enough modeling cement, it fit the end of the screen dowel too! This is by far the weakest link in my system so far, I will probably want to revisit it at some point.

I used some old wire wrapping wire to make a nice header pin for easy connections on the encoder bracket. It occurred to me that I might want to move this thing around, so making things modular was important.