Introduction: An Opaque Projector for Less Than $35

This Instructable will show you how to use a web can as an opaque projector for less than $35 (not including computer and display). We put this together as a quick and easy way to show a classroom full of people what is happening on the display of a small robotics controller.

Step 1: Gather Materials and Tools.

Rigid substrate (I used Extruded PVC sheet 0.25" thick, but you can substitute plywood)
Threaded rod - I used 1/4" - 20
8 - 1/4" - 20 Nuts
8 - 1/4" - 20 Cap Nuts

Hacksaw for cutting threaded rod
Tools to cut substrate (for the PVC it was a utility knife and drill)
Tape measure/ruler

Step 2: Cut Threaded Rod to Length

If you are using a fixed mount like I am, the first thing to do is to determine how far away the camera need to be from the base.  I did this by holding the camera by hand and looking at the image on screen and moving it up and down until I was at the height I wanted.

On a side note:  Focus on the the web camera is very helpful.  On our particular camera (a cheap Best Buy brand) there was no external focus ring.  I cracked the camera open and found that there was an internal focus ring, but it had a dot of epoxy on it.  I was able to take a knife and carefully break up the epoxy so the ring would turn.  Now that I had focus I could mount the camera at my desired height, about 6 1/2" from the bottom plate.

I added 1" to this measurement and cut my threaded rod into four 7 1/2" sections.

Step 3: Cut Substrate to Size

My controller is about 3" x 4", so I decided that a 5" x 5" square would leave me enough room for drilling holes and to hold the controller.

Cut two pieces the same size.

Step 4: Drill Holes in Substrate

Next you want to lay out and drill four holes in the substrate for the threaded rods to go through.

Mine are in the corners and two are wider so the CBC will slide in from one side.  Clamp both pieces together and drill them at the same time to make sure the holes line up.

Step 5: Drill Camera Hole

I initially drilled a hole in the center and then found the screen I wanted to capture was not centered, so I drilled a second hole and smoothed them into an oval shape.

Step 6: Put It All Together

Start with the base plate (substrate piece with no hole for camera).  Insert the threaded rod and screw a cap nut on the bottom.  Then screw a regular nut down from the top to pinch the substrate.  Continue this for all the holes on the bottom piece.  Then screw the regular nuts down from the top, put the top substrate and cap with the cap nuts on the outside.

Now you have the basic structure.  Mine is getting moved a lot and I do not want to adjust it, so I have used thread lock to hold everything tight together.

Step 7: Attach Camera

I used UGlu to attach my webcam because it is very strong, but I can remove it if I need to.

I plugged the camera into the computer and double checked that the view was what I wanted to see, and then UGlued it in place.

Step 8: Free Camera Software

Linux - Cheese
OSX - iPhoto
Windows - AvaCam

Open your camera software, and put it into full screen mode.  Now you can display the screen on the overhead!

This could also be useful to show small things like plants or small parts microscope style.

Step 9: Parts Cost

Threaded Rod - $  1.49
Nuts                   - $  1.49
Cap Nuts          - $  2.98
Substrate          - $  2.00
Web camera    - $24.99
Total                   - $32.95