The tree itself is pretty simple – a set of vertical strings of LEDs tapering in at the top to look like a Christmas tree.
LED strings and strips come in 15 meter (15-1/2 ft) lengths. The standard for strings is 50 LEDs wired together – this actually looks like traditional Christmas tree lights. Since this is for outdoor use it is a good idea to go with waterproof connectors. The test string I originally ordered came with interior connectors (foreshadowing).
Since the tree is still experimental I’m starting with a small tree, one around six or seven feet tall. I also decided to build a half circle tree since most people will only see it from one side. I decided to go with a design of 8 strings of lights for a half circle, 16 strings for a full circle. By building a small tree I can use a single strand of lights going both up and down, thus only needing to buy 4 strings of lights.
Surprisingly there aren’t that many choices for LED strings with waterproof connectors. I ended up with Rextin WS2811 strings.
You don’t just hang the lights from the tree. To ensure consistent spacing they make strips of heavy plastic that you plug the lights into. These strips have holes every inch allowing you to space lights two inches, three inches, four inches, or whatever you want. These mounting strips mechanically support the individual LEDs keeping strain off of the wiring – a good idea when you have long strings that may experience wind and snow loads.
It looks like this is a specialty item. While it is available from multiple sources they are identical – only 150 foot rolls and all vendors are exactly the same price. Whatever.
The first phase of construction is to cut a piece of the mounting strip to length and then stuff each individual LED into a hole in the mounting strip. A thick, heavy, strong mounting strip. The companies providing MegaTree kits have a special block to simplify this process. Being (relatively) cheap I discovered that a 9/16″ hole in a piece of 2×4 works well.
I had carefully designed the tree based on spacing the lights at three inch intervals. This makes a relatively inexpensive starter tree. Stuffing the LEDs into the mounting strip revealed that the wires were just a bit too short for three inch spacing – they could almost be pulled into place but with considerable strain. Krud!
After futzing around with the LEDs and the mounting strip I finally internalized that the initial design wouldn’t work. Back to the drawing board! Using two inch spacing with a full strand of lights for each vertical run would give me a roughly nine foot tall tree. And require twice as many lights…
Which wasn’t a complete disaster. Twice as many lights means four more strands. At roughly $15 per strand this still wasn’t too bad. Time to place another order.