Introduction: The 10W RGB Color Fading Chinese Lantern

My soon to be 13 year old son is a second degree black belt in Tae Kwon Do and loves all things asian. Thus his 13th birthday party was destined for an asian theme. My wife had most of the decorations covered but being the LED freak I am, I told her I had an idea...  Which normally gets a frown. In this case she was interested! I had also recently bought some 10W RGB plate emitter LED's from Deal Extreme that I had been chomping at the bit to use in something. Thus the RGB color fading Chinese Lantern was born. All I needed to do was figure out how to heat sink the LED, drive it with its rated current properly, make it color fade and mount it so I could light up the lantern.  Here is how I did it.

Step 1: The LED

Step One: The LED

The heart of the project are the 10W plate emitter LED's. I got these from Deal Extreme. I have also found them available from Aliexpress although I have not ordered this particular one. I have shopped from Deal Extreme for the past 4 years and have never had an issue.

The LED consists of  nine 1 Watt Red, Green and Blue LED's with 3 of each color wired in series. The controller I am using runs off of 12 VDC so the first step was to determine the correct current limiting resistors for 12 Volts. Red LED's drop about 2.2 Volts when forward biased with green and blue 3.3 Volts or so. Each string needs about 330Ma to produce its rated power.  I measured each string with a lab power supply at 350 ma of current. The red was 6.5 Volts, the Green 10 Volts and the Blue 10.5 Volts. I selected 22 Ohms for the red current limiting resistor and 5.6 Ohms for the Blue and Green. (Makes it a little simpler and easier to buy in quantity.) What power rating should I use? Power = Current squared times Resistance. So for the 22 Ohm resistor worst case we get P=(.350ma)2 X 22Ohms = 2.7W so a 3W resistor will work. The red will dissipate the most because it is the larger resistance.

The other thing to take into account is heat sinking the LED emitter. It must have a heat sink to keep its temperature down or the LED's will fail. I found some surplus 2”X1.75” heat sinks that are about 3/8” thick with a lot of little fins on them. They were originally for graphics cards. I figured they ought to be good enough so I bought a dozen of them. After an hour of use, the emitter plate was 50C and the heat sink warm to the touch so they are big enough.

Parts List: Alternate source: http://www.aliexpress.com/item/1pc-High-Power-Super-Bright-Integrated-RGB-LED-Light-Bulb-Beads-10W-Lamp-Bulb-Free-Shipping/704083925.html
Alternate source: Mouser http://www.mouser.com/Passive-Components/Resistors/_/N-5g9n?Keyword=5.6+ohm&FS=True

Step 2: The LED Module

LED Module Construction

I drilled and tapped the heat sinks to allow 4-40 screws to be used to hold the emitter plate. I bought mine a long time ago at Home Depot. Last time I checked, Lowes and Home Depot only carry the next size up a 6-32, which is too big.  You can get one on line from Amazon here:

http://www.amazon.com/Du-Bro-361-4-40-Tap-Drill/dp/B0006O4GYQ

A small drill press helps but you can drill with a hand drill if you hold the heat sink in a vise. Use oil when tapping or you will break the tap (I verified this one, which is how I know Amazon carries them...) Once the holes are drilled and tapped clean off any oil residue and mount the emitters with 4-40 screws. Now to mount the resistors and wire things up. Refer to the schematic for how the emitter gets wired. The controller we are using is designed for a common anode (+). This means the LED's are wired to the +12 VDC and the controller connects them to ground using an internal Mosfet. I used a short piece of wire to solder all the (+) leads together then directly soldered the resistors to the (-) leads of the emitter. The resistors are physically to large to directly connect without forming the leads to fit inward for the two outer resistors. In this case the Red and the Blue LED's. I used needle nose pilers and formed a little Z at the end of the 22 Ohm and one of the 5.6 Ohm resistors. See the pictures for details. For my prototype I left the resistors hanging and wired them up to the controller. I soon found that this was not a good idea as they broke pretty easily. So I bought some 5 minute epoxy and used a blob to hold the resistors in place. The epoxy is rated to up to 150C  so there wasn’t a problem.  When the epoxy cured, I soldered 15 ft of four conductor wire onto the resistors and the (+) lead using  small pieces of heat shrink tubing to insulate the connections. I terminated the other end of the wire into pins 1-4 of a male DB-9 connector so I could setup and break down the lanterns after the party. To hold the LED assembly in the right position I bent some wire from a clothes hanger into a triangle with about 4 inches of wire coming off the top. I bent a notch into that to hold the wire from the LED and to allow me to use a couple tie-wraps to keep everything in place. Now onto the controller.

Step 3: Modding the Controller

The controller is meant to connect to RGB LED strips using a small four pin header. Since I wasn't doing this and was going to use the controller for more than one lantern I needed to wire it differently. I needed to bring the leads out onto short wire leads that would let me use connectors that I could get a hold of. In my case DB-9 connectors. If you are permanently installing these you don't have to use any connectors, just wire directly.

Use a small screw driver to pop the case open. Carefully pop the circuit board out of the enclosure. It is held in by small plastic stops that can be pushed over to one side. There are two leads coming off of it. One for the IR sensor and the other one for the LED connections. That is the one we are going to remove and replace with wire leads. Remove the circuit board and flip it over. You will see a red, green, blue and black wire. The black is the common (+) lead and the others are the colors for the LED's. I used some solder wick to clean off the PCB holes. Unfortunately I found that the holes are too small to put a 22 gauge wire in so I soldered my wires directly to the PCB traces where the other ones were. Interestingly I noticed two things, first the original wires were not soldered through the holes either and, the other side of the board is labeled “R” “G” “B” but the red and green were different than the wire colors originally attached. One of the big complaints about these cheap controllers is that the colors are sometimes swapped. Once you have soldered on your leads or a long piece of 4 conductor wire, it is time to close the case back up. Carefully reinsert the PCB into the case while ensuring the LED wires don't get hung up. When the PCB is seated, you can pop the cover back into place.
For my lanterns I had two lanterns per controller so I then took my leads and spliced them into two DB-9 connectors. I used female pins on the controller side and male on the LED's

Step 4: The Non Electronic Stuff

Stands and a Base

I made stands for the lantern out of Bamboo. It happens to grow in a couple places near me in Dallas Texas. (I am sure it is not native!) and there is one place where people go to cut a piece for fishing poles and other stuff. I cut six pieces 7 feet long for the stand and then six 3 foot sections for a cross piece. I tried to lash them together using thick twine but it ended up being too flexible. So I used 2” angle braces I bought from Lowes and then covered them up with the twine lashed to get the look I wnated. Then I put small eye hooks at the end of the three foot piece of bamboo to hang the lanterns from. Now what to use for a stand to hold the bamboo up... I bought some two gallon buckets and some 2” PVC pipe and used concrete to hold the PVC pipe in the middle. This was probably overkill but I was running short on time and seemed like a good idea at the time.  Now I have six of these and I am not sure where to store them!

Step 5: Final Assembly

Open the package that the paper lantern comes in and pull out the two parts. There is the flattened lantern and a wire piece that pushes to two ends out to make a sphere. At the top are two metal loops that the wire piece pops into to hold the whole thing together.  Once the lantern is assembled, lower the LED assembly into the lamp and rest the heat sink on the bottom of the lantern. The lantern has an attachment point for the wire hanging down into it at the top. I judiciously put a tie-wrap here to make sure nothing slipped. Then I used a couple more tie wraps to keep the wire close to the bamboo and the base to try and hide it as much as possible. At the party, I used a red plastic table cloth (really cheap ones!) from Party City to cover up the base.

Step 6: Use

The controller comes with an  IR remote. Interestingly I discovered that even though all three of my controllers looked the same the remote buttons did not all work the same. One was different from the other two. There are multiple modes of operation and the one I like the most is the slow color fade.   Once you have the mode selected, there are +/- buttons to adjust the speed. Because all the LED's are so close on the emitter plate there is very good color mixing. The color fading lanterns were a big hit and I already have people asking if they can borrow them. I am glad I built them the way I did as the LED's can be fitted into other things for instant back lighting etc.  Enjoy!

Comments

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nisithc made it! (author)2015-05-22

yep.. i do it.. thanks for your post

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author
champagne51 (author)2014-11-04

very neat - I'm trying to do something similar but using arduino to control the LEDs - have you tried that config before? (I'm wondering if I would need a separate driver for each LED though..) - anyhow very neat!

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Bio: I started taking things apart when I was 6 started putting them back together at 8 and they actually worked again when I was 10 ... More »
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