This LED tree is powered by a USB wall charger and features slow changing RGB color lights. It's a good project to learn how to solder, as well as learning simple circuit concepts such as current limiting resistors for LEDs and power consumption.
I got this idea a few months ago when my fiancee and I were at the Charlotte, NC Makerspace (If you're in the Charlotte area, check it out! They had a lot of cool stuff going on, 3D printing robot parts, experiments/demos with superconductors, tesla coils, etc.). We made a similar project there, but I wanted to make one with more LEDs and slower changing LEDs. I also wanted to make this for my wife since we lost ours when we moved after getting married. She really likes it!
Step 1: Materials
Here's what I used to make it:
- 24 AWG magnet wire - 2 colors
- 30 color changing LEDs
- USB wall charger
- 5 15-ohm resistors (not pictured above)
- Solder fume extractor
- Wire strippers
- Soldering iron
- Helping hand tool
- 220 Grit sandpaper (not pictured above)
Here are links to where I bought some of the materials:
Step 2: Assembling the Tree
Start by cutting 30 strands of magnet wire from one spool and 30 from the other. 8 inches long is a good length for the longest ones. I made 15 of them 8 inches, 10 of them 7 inches, and 5 of them 6 inches. Having varied lengths makes the tree look more proportionate.
The reason you need 2 different colors of magnet wire is that one color will always be your positive, and the other color will always be your negative. I chose red to be positive. Each strand of red will match up with a strand of orange, so every LED has a positive "branch" and a negative "branch."
Once all your lengths of wire are cut, strip the enamel off of each end, about a half inch. Do this by folding a piece of fine sandpaper(220 grit) in half, putting the end of the wire in the crease, pinching it between your fingers and pulling it out. Repeat that on each end till the copper is completely exposed.
With all 60 of your wires (30 red, 30 orange) cut and stripped, separate the red into 2 piles of 15 and the orange into 2 piles of 15. Line up the ends of the 15 wires and twist them all together tightly. They should now stay twisted together. Solder the end that is twisted so that all the wires are connected electrically. Repeat this with the other 3 groups of 15.
Once you have all four groups of 15 soldered, make a 90 degree bend 1 inch from the soldered end. Now you can arrange the four with their soldered ends in a + pattern and twist the parts above the bend together to form the trunk of the tree.
Cut a 2 inch piece of wire of each color and strip their ends. Solder the red wire to both red "roots" so that all the red wires are connected. Do the same with the orange wire. Now all red wires should be connected to each other and all orange wires should be connected to each other.
Bend the branches however you want them to look, just always make sure you match 1 red with 1 orange wire. At this point you should have the basic shape of the tree.
Step 3: Powering the Tree
The basic shcematic is shown above. It is just a 5V power source (the USB wall charger), a resistor, and the 30 LEDs in parallel with each other.
Cut off the end of the USB cord that doesn't go in the wall charger. You should see 4 wires. The power and ground are the ones we want (red and black), so cut the others off. Strip the ends of the red and black cords with a wire stripper.
To figure out the resistor value to use, follow these calculations. If you don't want to get into calculations, just use the same components as me and you'll be fine.
We know from the LED Datasheet that the Forward voltage is 3.0-3.4 V. Let's assume 3.2.
The power supply is 5 V.
The resistor voltage drop must be 1.8 volts (5 - 3.2 = 1.8) (Use Kirchoff's Voltage Law)
Knowing the current of each LED (from the datasheet) is 20 mA, and we have 30 of them, the total current draw of the circuit is 600 mA (20 mA x 30 LEDs = 600 mA).
So the resistor has a voltage of 1.8 V and a current of 600 mA (0.6 A).
Using Ohm's Law, (V=I*R), solve for resistance: R=V/I = 1.8V/0.6A = 3 ohms.
So our resistor needs to be 3 ohms. There's a lot of current flowing through it too though, so we better check how much power is being dissipated through the resistor.
Power = Voltage*Current = 1.8V*0.6A = 1.08 Watts. Since the resistors I have are 1/4 W resistors, it would not do to use 1 of them (the resistor will probably burn out). To solve this problem, we can use a parallel combination of resistors to up the power rating. I used 5 15 ohm resistors in parallel. Using the formula 1/Rt = 1/R1 +1/R2 + 1/R3 +1/R4 +1/R5, solve for Rt and it's 3 ohms, but the power rating is now 1.25 Watts, so it should be able to handle it.
Back to Assembly:
Take the 5 15 ohm resistors and twist their ends together. Solder their ends together. Solder 1 end to the red cord sticking out of the USB cable and the other end to one of the two red "roots" of the tree. Now solder the black cord from the USB cable to one of the orange "roots" of the tree. Your circuit should be complete except for the LEDs now.
Step 4: Soldering on the LEDs
Take an LED and solder it's longer lead (anode or positve lead) to a red wire branch. Solder the shorter lead (cathode or negative lead) to an orange wire. At this point you can test your circuit by plugging in the USB wall charger and the USB cable. You should see your 1 LED light up. If not, make sure that none of the red ends are touching the orange ends, causing a short. If all is working, unplug it and solder 29 more LEDs.
Your tree is done! Enjoy it as you bask in its colorful and brilliant mood lighting.