If you have pets or children that you need to feed or check on via the internet, here’s a cheap and easy way to control motors, lights, and other devices at home from another computer online, like the one at work. You can set this system up in minutes and it requires no programming. All you need is a webcam, a flashlight, a standard computer running free software, and about $15 worth of analog electronics you can buy at RadioShack.

The system works through a Yahoo Messenger video chat connection between your home computer and any remote computer. But instead of showing people talking, the video stream conveys simple control information that you “encode” using a flashlight on a plain dark surface.

With my setup, for example, shining a light in the upper left corner of the image powers a dog food “allower” that uncovers a dog dish, and shining it in the lower right sounds a buzzer to signal dinnertime.

On the home computer, the video chat window runs full-screen, and cheap photosensors taped onto the screen’s surface detect the changes in brightness when the flashlight spot image hits their locations. Each sensor then switches its device at home via a transistor or relay. Voilà!

By using the screen itself as a port, you bypass having to unpack USB or some other protocol, and you can add additional actuators by simply taping sensors to different parts of the screen.

This setup also keeps your home computer more secure than remote desktop access software such as VNC, unless Yahoo Messenger has some super-secret way of controlling your whole computer, which is unlikely.