Download the Schematic:
I didn't do a step-by-step build for this demo because it is intended to introduce the underlying principles, not be recreated exactly as shown. A PDF download of the demo schematic, however, is available by clicking the link above. Mainly I wanted to keep things simple so you can take this knowledge and apply it to your specific application, since the details and requirements of individual applications are always unique. Because I didn't have a ready-made project on which I could demonstrate all three methods, I decided to break things up into three related demos. Each part covers one of three different, but handy, methods of automating door motion (Servo, DC Motor and Stepper Motor) and one of three methods of detecting the door-position limits (limit switch).
My friend and Parallax colleague Matt Gilliland built me these special laser-cut panels so that I could realize this project in a demo format. We stuck to a simple gravity sliding-door system that could be used for all three examples.
The control board and drive motor are at the top of the unit.
The power source is our Lithium Ion battery pack (designed by Matt), and I used a couple of momentary push buttons for control with a bi-color LED for status indication.
The door slides up/down within the frame with gravity pulling it down and the servo motor pulling it up. The limit switches are optical, which means they're based on light; specifically whether light is detected or not. Since we're using phototransistors that are sensitive to a wider range of light frequencies than just infrared, I shielded them from as much ambient room lighting as was possible with this demo design. The phototransistors are mounted on the back of the unit, recessed into the plastic. The IR LEDs are mounted on the front in the same fashion.
If you're using tact switches, you can connect those and the LED to the breadboard on your Board of Education (If that's the board you're using) and the LED as well.