LED Christmas Tree and Star: The LED Christmas Tree and Star project designed by The Spectacular Seven, a team of students from Oak Canyon Junior High in Lindon, Utah, won first place in the EE Times/IGEN Community Pride LED Contest. It features a small tree made from PVC piping, festooned with flashing LEDs on the branches and a star on the top, with a 7-segment display counting down to the New Year. The project uses not one but two microcontrollers, one each for the tree and the star.
Student notes: When we started this project as a group of friends, we had no idea how challenging it would be. We didn’t even know what 'LED' stood for. Now we know all about light-emitting diodes, resistors, the difference between NPN and PNP transistors, and much more. We learned how to measure voltage, program lights, solder, and how to use quality control. No one in our group really could have pulled this off on their own. It took a lot of "boring" videos, whiteboard diagrams, and lots of notes to scratch the surface of understanding the LEDs.
We wanted to control all of the LEDs individually from the microcontroller so that we could do some fun light patterns. After counting the LEDs (32 of them) we found that we did not have enough control lines from the microcontroller. We discussed ideas and learned about a way to multiplex. Each of the eight branch levels would be tied to eight transistors on one side and each of the four sides of the tree would be tied to four more transistors. We also learned about persistence of vision that helped us to have more than one LED appear to be on at a time.
The programming of the lights was the most challenging part of the project. Only a little part of the programming system is tangible. From going from our heads to the lights on the tree, there are many steps to take. First, identify every light. In order to know which light is which, every one needs a name. Second, create a sequence. A sequence is a binary code that turns certain lights on (1) or off (0). Third, type the sequence patterns into the computer.