Step 12: Final Assembly
Wiring the Pot
Both the pot and the Arduino should have leads attached by this point, unfortunately it isn't as simple as connecting the two sets of leads. You need to make sure that when the screen goes up the pot is reading in the right direction and vice versa. To do this you need to decide which side the motor will be on when you face the screen. Then run the app and select either up or down and note which way the rod turns. At this point I used trial and error since there are only two possibilities and hooked the pot up to the Arduino using temporary connections. Now with the pot, NOT engaged in the rod, turned all the way to what should be the up position try running the screen up. It should ignore the command, if it does you are good to go, make the pot connections permanent. If it starts to run you need to simply switch the V+ and GND wires between the Arduino and pot. Do this and test again to make sure, then make the connection permanent.
You can also orient the motor and pot directions by modifying the Arduino sketch and the Android app but honestly it is much easier to swap the polarity on the pot.
Attaching the Screen
My pictures show the rod attached to both the housings in a few of the pictures pertaining to attaching th screen, in hindsight it is easier if you remove the housings and just place the rod on the floor. Just make sure the motor shaft's flat is facing up and the set screw hole on the rod should facing up too.
Finding the width of the screen is easy, simply measure the available length of the rod, leaving .25"-.5" on each edge, mark the width, and cut.
For the height you need the correct length that keeps the screen in aspect (16:9) plus you need to compensate for the distance between where you want the top of the image and where the rod will sit. Longer is better because you can either cut some off the end or keep some rolled up in the next step, calibration.
With the screen cut to size (and ironed if necessary) push the edge up to the rod so that it is in contact with the rod (check the pictures, they are probably clearer). When placing the screen you need to take into account which way the rod will be turning and which side of the material will be projected on. When everything's facing the right way and the screen is as square as possible to the rod, place small pieces of tape along the length to hold everything in place. Use an automatic center punch or knife to mark the place where the screws will go through the screen, near each edge and 6"-10" apart in between. Widen the holes in the screen by pushing the center punch through and then place a screw and small washer in each position. Once all the screws are in you may want to trim, or tape down, the edge of the screen that sticks out past the screws. It tends to stick out and then the screen doesn't roll up as cleanly.
Assembling the Pieces
This one is easy, I promise. Before you start, turn the potentiometer all the way to what will be the down position, then turn it back a 1/2 turn. Put the motor's shaft in the proper place, tighten the set screw (onto the shaft's flat if it has one), and press the potentiometer into the grommet on the opposite end.