Ovidiu Predescu's Weblog

Remote controlled projection screen

After spending two months researching, designing and implementing, I finally finished my home project: a remote controlled projection screen system. Here are some pictures of the whole system, as well as two videos, of the system extending and retracting.

What was interesting in this project is that it required a lot of mechanics, electronics and programming to be implemented. Since I've never studied mechanics or electronics (OK, I actually took some basic classes in high school and university), these have been the most challenging and fun parts of the project.

The basic requirement was to have the screen sit on top of the multimedia cabinet, slightly retracted. When I want to make a slide film projection, the system would extend the screen about 10" in front of the cabinet, and allow the screen to drop. The whole system would need to be remote controlled through a regular IR remote, as the cabinet is pretty tall.

The basic design started by choosing the projection screen. I chose a Draper Salara matte white 84" x 84". This was the only projector I found that had the screen attachments flexible, all others had them on either side of the screen. I got the screen from projectorzone.com, the only company that allowed me to get the very basic package (screen only, no remote controls whatsoever).

The next step was to design the system to perform the horizontal movement. After investigating linear actuators, I decided to go with a much simpler, home-made rack and pinion mechanism. This needs to move the projection screen horizontally about 15" (~38cm), and is powered by a small DC motor. Here is a small program in bc that I used to size the motor. The actual mathematics used in the program comes from here (look for motor selection and sizing). I bought the parts from mcmaster.com, an excellent source for mechanical parts. The DC motor, as well as most of the wires, electronic components and others I bought from jameco.com.

To control the movement of the whole system, I chose to use a BasicStamp system. This component receives inputs from an IR sensor from the remote control, two limit switches to indicate when a horizontal movement should stop, and an IR emitter/receiver to limit the movement of the vertical screen. Here is the program to control the whole system.