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3D LED Christmas Tree Build

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Last year I ordered a couple of these 3D LED Christmas tree kits from SainSmart at the same time I ordered one of their Fukubukuro mystery bags.  There are a variety of LED Christmas trees around ranging from this cheap version on Amazon up to a limited edition one offered by Particle that is web connected.  Some of the really basic ones have standard single color LEDs which does not sound all that interesting.

This version has 37 “7 color” LEDs which individually fade between 7 colors: red, green, blue, yellow, something I will call teal, purple and white.  Each board has 18 LEDs divided into groups of six that are driven by 3 basic RC oscillators to make them blink.  The capacitor and resistor values for the oscillator are pretty flexible and will change the flash rate.  Higher values will increase the frequency, lower ones will decrease it.  Small variations in individual components will make each section blink differently and the oscillators on each panel are chained such that they will be out of phase with each other.

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Similar schematic, but component values are different than what I got with my kit

I tracked down the instructions just to make sure I got the resistors in the right spots.  This took a minute because something seems to be a bit broken about the search functionality on the SainSmart learn site.  I won’t detail every step because it has already been covered over on Hackaday.  It is a slightly different revision, but the same basic process.

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Components laid out: 39 LEDs (2 extra), 7 transistors (1 extra), 6 capacitors, 13 resistors (one value for current limiting and the other for the RC oscillator), power jack, switch and three circuit boards

The printing on the boards makes it pretty clear how to assemble besides which resistors go where.  Once I verified how to do the resistors, I worked my way through populating one board.  I recommend doing resistors first even though I forgot this at first.  If you put in taller components first, the resistors like to slide out of the board.  The LEDs have a flat section in the leads so there is no concern about leaving a consistent amount left to allow them to bend over.

With one board finished, I applied some power to the pads to ensure that everything worked.  It is much easier to make fixes before the two boards are assembled.

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The LEDs all start on red bit quickly get out of sync from each other.  You can see on this board where I laid the one capacitor down to avoid conflict.

I did have one set of 6 LEDs on one board that didn’t work initially for some reason.  I checked for shorts and the resistor and capacitor for that section, but nothing jumped out.  I removed the transistor and tried applying voltage directly to that section, but it still wouldn’t light.  I decided to check each LED individually.  I removed one and it tested out fine.  I checked the remaining 5 again before continuing and they also worked.  I reinstalled the LED and everything now works.  I still don’t know what the problem is, but I am glad it is working.

The lower board is setup so you can power it with a mini USB plug or the included battery pack.  I set the battery packs aside for now since I expect I will have them near usb ports or on outlet for now.

When I went to put the upper boards together, I discovered a mistake.  I had gotten carried away and installed the top LED even though it spans across the slot where the other board needs to slide it.  It only took a minute to remove one side so I could put them together and then resolder.  I also found one other minor problem–a couple of the capacitors would like to occupy the same space.  I recommend leaving some room to bend them down flat even though the printing on the board might lead you to solder them close like I did initially.  I saw a picture of one board somewhere that is printed to indicate laying the capacitors down.  The transistors did brush past each other a bit, but it is not really an issue.

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With the tree assembled and fully functional, it was time to put it in the acrylic case.  Peeling the protective films off of these sorts of pieces is always a test of patience.  Once that was finally complete, I set to mount the tree on the bottom section.  I found that the standoffs have to be put in so the nuts are on top of the circuit board and the screws are through the acrylic plate.  If they are the other way around it just won’t fit together.

Assembling the case is just what I expected after building similar cases before.  Each corner takes a bolt with a nut to hold it together.  The nut needs to be slid into the slot (carefully so it doesn’t fall in) and then tighten the bolt into it.  I do have two issues with the case.

First, the front and back panels are identical, but this puts the hole just a little too high and not wide enough for the supplied cord.  A different cable might almost fit but the hole should be at least a few millimeters lower, so I broke out the Dremel to fix it.  Using the battery pack would work just fine.  Secondly, the case is not quite large enough for the bottom lights to fit without being adjusted so they don’t stand straight out.  Everything still functions, but I would really like it if all the LEDs could line up perfectly.

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If you look, there are no rear panels yet.  I had not yet modified them to fit the power cord.

Despite the small issues, I am happy with the results.  I brought one with me to work and left one at home.  Everyone loves the look of it and I have a coworker that ordered one of his own.  If you would like to get your own, you can get one from SainSmart.  They also have one now that is taller and plays music.


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