Step 5: Potentiometer Circuit
Your pot should have three posts, make sure there is a lead wire attached to each one. These wires will probably need to be fairly long, as they will eventually reach from one end of the screen to the other where the Arduino is located. For now just attach jumpers to the pot and plug them straight into the Arduino. The three posts on the pot should be arranged with two on the outside and one between them. Connect the V+ pin to the 5V Arduino pin and the V-, or GND, post to the Arduino's ground pin. The third, or sweep, pin is attached to an analog pin, I used A0. The motor shield I bought covers all of the header pins on the Arduino but breaks them out on the board. This is fine, it just means I had to solder the pot to the motor shield for the final build. For testing the pot I just attached the pot straight to the Arduino's headers.
The attached test program uses the pot to control the built in pin 13 LED on the Arduino in a similar fashion to how it will control the motor in the final program. The program sets the top and bottom 5% of the analog input as thresholds, then as you sweep the pot the LED is on between the thresholds but turns off when you get close to the limits of the pot.