LED Christmas Tree
Abstract
The objective of this project is to demonstrate the skills and knowledge acquired with the use of Dip Trace, soldering, chassis manufacturing, as well as troubleshooting any potential problems. The completed project used one of the boards returned from manufacturing without any need for alteration. The chassis used for the project was designed in CAD software and printed on a rapid prototype.
Project Description
The Through Hole Christmas kit from sparkfun includes nine bright green LEDs, 1 yellow LED, a resistor, battery pack, large Christmas tree shaped PCB and a pre-programed AVR integrated circuit. Once the IC is powered on it begins the pre-programed routine that flashes 3 green lights and the yellow light using pulse-width modulation to fade the green LEDs. After 3 different sets of green LEDs light and dim the system goes into a sleep state for approximately 15 seconds at which point it repeats the illumination and dimming of LEDs.
The board was designed to mimic the shape of a Christmas tree with the yellow “star” LED resting on the top of the pyramid shape. The IC was positioned such that it mimics the appearance of a trunk of the tree or a present like the resistor and power lead pads. The libraries of parts were recycled from the previous continuity tester project as well as utilizing the built-in AVR library for the ATtiny85 AVR chip.
The Chassis was developed such that it could be printed on my 3D printer, a RapMan 3.0 from Bits From Bytes. The chassis was designed using CAD software then exported as a STL file. This file was then run through a “slicer” program which takes the digital geometry and slices it into thin layers then computing the path for the head to move through to print the layer. After the g-code is done being created it is placed on a SD card and executed on the printer. The ABS is heated and fed into the heater barrel forcing molten plastic out the small orifice where it bonds with the previous layers.
With the board populated it was attached to the chassis with four #4-40x1/2 screws. When mounted the board, resistor, and IC are all below the edge of the protective protruding perimeter while the LED tips protrude beyond this plane and are therefore visible from the side.
Conclusion
This project provided both problem solving and creative thinking applications in electronic design as well as the mechanical design and build. For the electronics I chose to use the “think smarter, not harder” approach using the tools available to me to develop the library needed to design the board. When it came to the chassis design and manufacturing I wanted to use my rapid prototype and therefore had to keep the limitations of the machine in mind when designing the chassis on the computer. With a lack of support material overhangs can be a difficult feat to overcome when printing. This was overcome by printing several small test patterns with different overhang angles where I determined that a 45° overhand could reliably be printed. This can be seen in the attached drawing toward the the battery pack “port”.