LED Color Mixer – Make and Take

Tomorrow, Saturday 10/4/14, is the fall meeting of the Michigan Section of the American Association of Physics Teachers. If you’re interested, it will be at the University of Michigan, Flint. For more information you should check out the meeting page.

Anyway, Jim Gell and I will be running a Make and Take in the afternoon. One of the things we will be doing again is the ever popular LED Color Mixer. We’ve done this before as a modified version of the LED mixer presented by Chris Chiaverina in the Physics Teacher. This is a pretty cheap demo device, but in the past we ordered $1-2 LED, $1 battery holder, $0.50 ping pong ball, and 2 AA batteries. Cost for each one was between $3 and $4. This was a bit costly to run as a Make and Take. It also involved soldering, which while not particularly difficult did require the direct supervision of someone.
We will be doing the same project on Saturday at a cost of less than $0.20/device with no soldering required. This project is cheap enough that you can have participants make one on site and then send them home with a couple extras to make with their classes. They’re so cheap that a teacher could have each of their students make one to take them home and explain how they work to their families.

The parts list:

I should note that while both the batteries and LEDs are sourced from Amazon, the LEDs come from China and will take a few weeks to arrive. While the LEDs are cheaper than we’ve been able to get them in the past the real savings is from the batteries. In order to make things extra cheap I replaced the ping pong ball with a paper cube.
Simply bend the leads on the LED as shown. The shorter of the two leads goes to the negative side of the battery with the longer going to the positive. Use a little electrical tape to hold the leads to the battery. If needed, slip a small strip of overhead transparency in between one lead and the battery to act as an “off switch”.
Print out a copy of the 2.25″ Cube Template and assemble. Before closing the last flap put 1/2 a Kleenex in to help diffuse the light and cut a hole in one side. The simply slip your LED and battery in and bask in the color changing goodness you have created.
How would you use this with your students? Share your thoughts in the comments.