This little project makes a great ornament to hang in your window at Christmas time. It is a 20″ wide star with 50 “neopixel” leds around the perimeter. Each led is individually addressable and it is controlled by an arduino device which can be programmed to sequence the leds in various patterns.
Depending on where you live you may be able to get all or only a few of the items required so I will try to list out some sources at the end as well as links.
I have always loved to tinker and build things. I find myself in a position now where I have quite a bit of time on my hands so I resurrected an old hobby of mine, electronics. With the Christmas season fast approaching, I wanted to do a few cool things and what better way than lights, lights and more lights? I’m still at the beginning stages of learning about micro controllers and how to program them but incorporating the learning along with a project makes it quite enjoyable. I won’t cover all the bases here regarding programming and general electronics but there’s a wealth of knowledge available on the internet and its just a quick Google away. Have fun and let me know what you think.
Ok, on with the show.
Step 1: Materials and tools
I’ll provide some resources for sourcing some of these items later in the article
- Arduino Uno or other compatible micro controller ( I used the OSEPP Uno R3 but will switch over to a Pro Mini for the finished version). You can use the genuine Arduino but there are lots of other clones out there that are a lot cheaper
- RGB Led pixel string 5volt, prewired, 50 leds with ws2811 controller chip. Use waterproof string for outdoors
- Small prototyping breadboard (optional)
- 300-500 ohm resistor (330, 390 or 470 ohm are standard values)
- 1000uf 16v electrolytic capacitor (can be a higher voltage rating eg. 25V 35V 50V)
- 5 volt power source @ 2-3 amps (make sure it is at least 2 amps)
- Connector for the power plug
- jumper wires
- 20X30 posterboard with metallic film on one side (or any other medium that will support the leds)
- Xacto or Olfa knife, scissors, tape, pencil, ruler, tape measure, paper, straightedge drill and drill bits-3/16″ and 7/16″, small sharp punch
- If you want to make a permanent version then you will need a soldering iron and solder
Step 2: Building the star – cutting it out
NOTE: You’ll notice that with some of the dimensions, that the numbers don’t add up exactly. This is because when the cad program inserted the measurements, it was set to display in 1/16″ increments. If a measurement is say 5/64″ it would display 1/16″ instead. This minor amount won’t be noticeable.
The first thing to do is layout the star. I added a radius to the tips of the star. This way I could fit a bigger star into a 20″ X 20″ square. The layout was done on the computer using Deltacad, a small easy to use cad program. You won’t need to learn it for this project but you can download a demo copy which is good for 45 days. I’ll include the cad files in this article so you can view them or print out the measurements.
I used an Elmers holographic foam board (20″X30″) as the star. I suppose you could use anything that is stiff enough and not too thick but the foamboard is fairly easy to cut and work with. I got mine at Walmart but I’m sure it is available at lots of craft stores. Transfer the sizes to the foamboard (backside without the metallic foil), draw in the lines and then your ready to trim it to size. Make sure you draw it all out first and then check to see that it looks all symmetrical. It’s easy to goof on a measurement. Remember the golden rule: measure twice, cut once. I used an Olfa knife to cut the board. Lay a straightedge along the lines you want to cut and then score the board. Be careful not to go all the way through on the first cut and make sure you have something underneath to protect the surface you are cutting on. You don’t want to start carving up the new dining room table!! After you have scored all the lines, cut again a little deeper. The idea is to cut deep without going all the way through. Cutting all the way through can end up leaving a jagged edge on the foil. After the scores are deep enough, cut all the way through on the ends of each line. this way you can see the start and end of each line from the foil side. A smaller knife is handy here. Xacto makes a great little hobby knife. You can get them at Staples among other places. Now, you can switch over to the foil side and score through the foil from the top, which will help keep it from distorting. Be very careful to make sure you are cutting the right lines or it’s back to the store for more foamboard. After the star is cut out, you can radius the tips with the knife and clean up the edges a little. Note: the drawing doesn’t show the radius tips but that can be done easily by eye after it’s cut out.
Step 3: Laying out the holes
The center of the holes run along a line 3/4″ in from the outside and are spaced 1 3/8″ apart. This gives a total of 50. Convenient because the pixel strings are available prewired in strings of 50. Layout the holes and then use a fine punch to push a small hole through the board (again, this is done from the back side. Now, drill a pilot hole about 3/16″ or so all the way through. Then, from the front side, drill through again with a 7/16″ bit. Do this carefully as you don’t want to tear up the foil. The specs for the leds call for a 12mm (1/2″) hole but because the foamboard is soft, a smaller hole tends to keep them tighter. Because it is foam, a type of plastic, drilling tends to heat up the material. This results in it melting somewhat. We are also dealing with the foil and glue that holds it on so in the end, you won’t get a nice clean hole. I used the razor knife to clean them up a bit and get the larger loose bits off but by the time it’s all done, you won’t really notice the rough edges. I was thinking of sourcing out some kind of punch but in the interests of time and budget, I went with the drill. You can layout the holes with the measurements provided or if you get a copy of Deltacad and download the cad files, I’ll include a full size layout of one point of the star. This can be set on the drawing and used as a template to punch through the hole location.
Step 4: Installing the Leds
If you haven’t worked with these kind of leds before, be careful or your project won’t work or will run in reverse. Make sure they are of the WS2811 variety and use 5 volts. They come prewired in strings of 25, 50, 100 or more. There is no standard for wiring order or color code so you will have to determine this yourself if there is no documentation with them. The pixels have a starting point and an ending point, often terminated with a small plug. Inside the pixel is a RGB led, a WS2811 integrated circuit and a resistor mounted to a small circuit board. If you look at the closeup photo, you can see the wiring at the top. There are 3 wires in and 3 out. On each side you should see where they attach to the board. One side is the input while the other is the output. On the kind used here the input pins are labeled GND (ground) DIN (data in) 5V (+5volts). Mark the backside of the star with TOP at the end of one of the points. This top hole will be #0. Then, going clockwise, number the holes (#0 to #49). Push the leds into the holes until they protrude out the front far enough that they will be seen. They have a small nub on each side that will help hold them in. You may have to clean up the holes a little. If any are too loose, you may have to use something to glue them into place such as silicone. A good idea is to try them in a sample hole. If you used the 20X30 foambard, there will be a 10″ strip left over that you can drill some sample holes into. I had no problems with the leds being to loose. Unless you plan on using the led strip elsewhere, you can also snip off the end plug leaving some wire on both it and the strip. This way you can attach it to your controller circuit and then simply plug it into the led string.
Read more: Led Star with Arduino and WS2811 Neopixels