The little tree has candy canes on the silkscreen, ornaments made out of exposed copper, and a trunk made out of exposed FR4. The garland is made out of resistors, and the lights are LEDs, powered by a micro USB connector on the back.
You can hang the ornament on your tree by putting a string through the hole at the top of the ornament. Or, you can use it as a standalone decoration, in which case the USB cable in the back acts as a sort of "kickstand" to hold the tree up.
This README should contain enough information to build the ornament. However, if you want more detailed, step-by-step instructions with pictures, I've also written an Instructable on how to build the ornament.
Bill of Materials
USB Micro B connector, qty 1. Würth part number 614105150721. Digi-Key part number 732-5958-1-ND.
1/8 watt resistors, qty 14. Make sure the length of the resistor is around 3.3-3.6 mm. The minimum resistor value you should use is 150 Ohms. However, I found that to be too bright, so I eventually settled on 1k Ohm resistors. Especially if you use different LEDs than I did, you should experiment to see what resistor value gives you a brightness that you like. For 1k Ohm resistors: Stackpole part number CF18JT1K00. Digi-Key part number CF18JT1K00CT-ND.
3mm LEDs, qty 14. Just about any 3mm LED should do, but I used color-changing LEDs to add a bit of motion to the ornament. When soldering the LEDs, make sure the short leg of the LED goes into the square pad, and the long leg of the LED goes into the round pad. For color-changing LEDs: SparkFun part number COM-11448. Digi-Key part number 1568-1196-ND.
Optional: 3.3µF 0805 ceramic capacitor, qty 3. These probably aren't essential, but since decoupling capacitors are considered to be a good idea, I added pads for three capacitors on the back of the board. (Though if you're using ordinary LEDs, you really don't need them, since the current will be constant. I only added them because I'm using color-change LEDs, which probably use PWM to fade through the colors.) Unlike all the other components, these are surface-mount, so they're a little trickier to solder. It helps if you have a second person to hold the capacitor in place with tweezers, though it's possible for one person to do it. Samsung part number CL21A335KPFNNNG. Digi-Key part number 1276-6461-1-ND.
Optional: string to hang the ornament. Just about any string should do. I used Hemptique red cord.
And, of course, you'll also need a USB charger and Micro B USB cable to power the ornament.
Most fabs should work fine, although you'll probably want a fab that offers green soldermask. (That rules out OSH Park, unless you want purple trees!) I went with EasyEDA because they are inexpensive and offer green soldermask. (However, it appears that EasyEDA is spinning off their circuit board manufacturing to the site JLCPCB.)
I went with a PCB thickness of 1.0mm, because that's what the datasheet for the USB connector recommends. (With a thicker PCB, the pins of the USB connector won't protrude all the way through the board.) I chose the more expensive ENIG finish, because I thought that would look better on the exposed-copper ornaments.
If you're not making any changes to the board, all you need to do is
zip up the files in the
gerber directory, and upload the zipfile to
EasyEDA. After uploading the zipfile, these are the options I chose
on the EasyEDA site:
Note that in the KiCad files and Gerber files, the "front" of the board is actually the back, and vice-versa. This is because EasyEDA adds a customer ID number to the front of the board, but I wanted the number to be on the actual back of the board, where it doesn't disrupt the esthetics of the ornament.
I recommend ordering more boards than you need, because some of the boards will have cosmetic defects. (They still work fine electrically, but just don't make an ornament that looks as nice.) In particular, the FR4 appears to have some red writing on it in places, so every now and then that will show up in the trunk of a tree.
Another way to solve the problem of the red writing on the FR4 is to paint the trunk. (e. g. with flat brown Testors enamel paint)
This design is licensed under the Creative Commons Attribution-ShareAlike 4.0 International license.
Other circuit board trees
I'm not the only one to have had this idea. Here are some other folks who have made tree-shaped Christmas ornaments out of circuit boards:
However, I feel that my version has some advantages:
- More LEDs - My version has 14 LEDs.
- "Cleaner" front - Mine has all the circuit traces on the back, so the front is more esthetically pleasing.
- USB Powered - Mine uses a USB charger instead of a battery, so you can plug it in with the rest of the lights on your tree.