This is a different way to control your computer using a laser. Unlike [http://www.instructables.com/id/Control-your-Computer...-with-a-LASER!/ icinnamon's] way, this uses a webcam and a laser to control the cursor on your computer. You can even click by simply turning the laser off for a split second.
Step 1: Download the software and get a laser or IR pen.
First you must download Microsoft Visual C#.
After you have Microsoft Visual C# downloaded, download Laser Interaction. The file name will probably be really weird, so rename it Laser Interaction. Now you will need a laser or IR pen to use it. The first picture is a schematic I made of a simple IR pen you can make. I am using a 100 ohm resistor because I am using 5 volts from a USB cable. You need to have a momentary pushbutton switch on it. I used a normally opened switch so when I press the button, it will click. I also bought a cheap $5 dollar laser from radioshack. I'm sure you can find one cheaper, but I love radioshack stuff.
Step 2: Deciding what to use and how.
You can use either an IR pen or laser, but they require different setups of the webcam. If you are using a laser, you must put your webcam somewhere so it is pointed at the wall. If you are using an IR pen, your webcam has to be pointing towards you when you use it. If you use an IR pen, you also have to go into the webcam settings and make it so the image is mirrored horizontally. I am using a logitec quickcam for this project, but you can use others as well.
Step 3: Running and ajusting the program.
First, open the Laser Interaction folder and there is an icon named motion that opens Microsoft Visual C#. After it opens, click the run button. After that, a window will pop up. Click file and then click open local device. This will pull up a list with the name of your camera. Click ok and it will show the image on the box. Them, you will have to adjust the brightness threshold until the only thing the software "sees" is the IR pen or laser. You will know when you have achieved the right threshold when the program only puts a circle around the IR pen light or laser dot. Try to make the threshold as low as possible though for optimum performance.
Step 4: Final Adjustment
After you adjust everything, go into control panel, and folder options, and make it so you can open things with only one click, because the program only currently clicks once. After that, check the boxes control cursor and enable click. Now, your laser or IR pen will control the cursor and click. Just make sure if you are using a laser, the webcam is pointing at the wall and for an IR pen, you have it pointing towards you and the image mirrored. Move the IR pen around away from the screen and the cursor will move. Move the laser around on the wall where the camera can see it and the cursor will move around.Now there is no need for a mouse. Please vote for me, as I put a lot of work into this instructable. It's not as accurate as others like the ones using wiimotes, but it works.