Introduction: RGB Color Controllable High Power LED Room + Spot Lighting
- Controller can power up to 360 watts of LED lighting - between 3 and 100+ power LED's
- Analog dial or slider for Red, Green and Blue - create an infinite number of light colors!
- easy to make a room light or a spot light by switching lenses / covers
- very fine analog control for precise color matching (or white matching)
- Includes current-limiting protection circuit
- Simple 7-component thru-hole circuit - No microcontrollers or programming!
- Controller cost: $25
- 50-watt, 15-LED lamp cost: $50
- Efficient: 50 watts of LED light equals 100 to 150 watts of incandescent light.
- Efficient: 80-90% controller efficiency
- Controller can be used with a variety of power sources
- Recycled materials & electronics: 20-40%
I've included a lot of detail in this instructable that applies to any power-LED project, and i've got several other power-LED instructables too, check those out for other notes & ideas.
why not digital?? this controller was specially designed to be as simple as possible by using analog-only. it turns out that it works really well. yes, a digital PWM controller is "better", but it requires "chips" and is thus more complicated to build. i've included a circuit for a digital PWM controller here.
This article is brought to you by MonkeyLectric and the Monkey Light bike light.
Step 1: How Does Color Mixing Work?
this step explains some of the basic science behind how you can make an 'any color light' using the common technique of "color mixing".
lets start with your eye, which is an incredibly complex and sophisticated image sensor. how does your eye see an image? your eye has millions of individual sensor cells, a bit like the pixels in a digital camera sensor. your eye has 2 major types of cells: rods and cones. there are about 100 million rods, they are very sensitive to light but only see black and white images - they are your night vision. there are also about 5 million cones, which come in three types. each of the three types of cones sees different colors. you can think of the three types of cone sensors as 'red cones', 'green cones' and 'blue cones', although this is a bit of a simplification of how it really works.
so, how do we see colors? every color you can see is a result of how your brain interprets the signals it gets from the three types of cones. if you look at something and only your 'red cones' see it, then your brain sees red. if you look at something and both your 'red cones' and 'green cones' see it, then your brain interprets yellow. every color you can see is the result of how the brain interprets the different strength of signal from the three types of cones.
how does that help us? it means that using only three different colored lights (red, green and blue), we can easily fool the brain into thinking it is seeing any possible color. lets say we have a real yellow light: this light activates both the red and the green cone sensors in a specific proportion. but we can also activate the red sensor with a red light and the green sensor with a green light. if we activate the two sensors in the same proportion that the yellow light would have, then our brain can't tell the difference from a real yellow light and we see that red plus green equals yellow. we've fooled our brain!
it turns out that this is a very popular trick. every color television and computer screen ever made uses this exact principle! also most printers, cameras, and other imaging devices are based on this principle. if you have an older 'tube' screen or a plasma screen - look closely at it while it is displaying images and you can see all the small red, green and blue pixels (a magnifying glass helps).
for more information:
Step 2: What You Need
electrical components for the three color channel controller (Red, Green, Blue):
- 3 x Q1: small NPN transistors (digikey: 2N5088BU)
- 3 x VREG: adjustable voltage regulators (digikey: LD1585CV or LM1084IT-ADJ)
- 3 x control knobs: 2k-ohm to 10k-ohm linear-taper potentiometers (see following steps)
- 3 x R3: 2-watt resistors (see following steps)
- 3 x R1, 3 x R2: resistors (see following steps)
- 4 x C1: 47uF 35V capacitors (digikey: ECA-1VHG470)
- Red, Green and Blue High-power LED's ("Star" type - see following steps)
- 8-position terminal block: digikey: 39100-0808
- solderable prototyping board: these come in many styles, you will need about 1" x 3" size to build the circuits. try digikey: "vector V2018", which includes column-busses that will make the wiring a lot easier than what i did. i used digikey: "twin industries 8000-45", which is a lot more of a hassle, i just had one lying around.
- project box: i used a large-size electrical junction box, cheap and widely available. a metal box is important to allow cooling of the controller. if you have a plastic box you will likely need a fan in it.
- project box cover: use the one shown with a cut-out to fit "slider" controls, use one with no cut-out for dial/knob controls.
- strain relief for project box
- power supply: recycling an old laptop power supply is ideal, especially if it has a broken tip. any power supply between 12V and 25V DC with 2 Amps or more is good, between 20V and 25V is the best (which is what most laptop supplies are)
- heatsink: a large piece of scrap aluminum with enough flat area to mount all the LED's. some thin mylar (polyester) sheet is needed as a heatsink insulator, a good source for this is the mirror-type static-shielding bags, or window-tinting film. you can use thermal compound, but it isn't required.
- adhesive: "GE Silicone II" from the hardware store is a good high-temperature adhesive for heatsinks.
- optics: for a room light, some form of lampshade will be needed, or you can use the cover from a 4-foot fluorescent fixture. for a spotlight, use L2optics lenses on each LED, these are cheap and can focus the beam as needed (see LED selection step).
- wire: you'll need about 6-12 inches of 18-22 guage high-temp (90 C or better) hookup wire per LED. you could get this from digikey: "carol C2117-12", but that's really overpriced. you can get 18-guage high-temp wire by ripping apart a standard 18-3 SJOOW rubberized power cord from your hardware store. you'll also need enough cheap wire to make a 6-conductor cable between your lamp fixture and the control box - i made a 15-foot cable using 45 feet of cheap 18-guage lamp cord.
Step 3: Selecting the Power Supply
This step helps you figure out:
- what power supply to use
- how many LED's to use
How big a light can you make? It all depends on your power supply. you need a power supply between 12V and 25V DC, and 2 amps minimum. more amps lets you use more LED's, and the high-end of the voltage range will let you use more LED's and be a bit more efficient also.
Old laptop power supplies are the best because they are usually between 18V and 24V, and are small, efficient and fan-less. you can usually extract a boxed power supply from most larger electronic equipment such as desktop computers, these will at least get you 12V with lots of current. check the sticker on your power supply to see what its specifications are.
Voltage: this determines the number of LED's in series you will need. we will put the LED's in series strings so that each series string uses close to the power supply voltage when running at full power.
Current: this determines the number of parallel strings of LED's you will have. you need 3 minimum: one each for Red, Green and Blue. Count 600mA for 1-watt LED's and 1200mA for 3-watt LED's, so that means the minimum current for your power supply is 3 x 600mA or 1.8 Amp. If you have more than double that, you can put more parallel strings of each color (but you don't have to if you want a smaller light). you'll run your LED's a bit less than this, but you need some "spare" capacity to avoid burning out the power supply.
ok, so how large will our series LED strings be? start with these figures (calculated using the LED forward drop, plus a 1.5 volt overhead):
12-volt power supply, luxeon-1 up to 300mA LED current, or lux-3 up to 600mA
4 x red, 3 x green, 3 x blue
12-volt power supply, lux-1 up to 600mA
3 x red, 3 x green, 3 x blue
18-volt power supply, lux-1 up to 500mA
5 x red, 5 x green, 5 x blue
20-volt power supply, lux-1 up to 500mA
6 x red, 5 x green, 5 x blue
20-volt power supply, lux-3 up to 700mA
6 x red, 5 x green, 5 x blue
24-volt power supply, lux-1 up to 550mA
7 x red, 6 x green, 6 x blue
24-volt power supply, lux-3 up to 800mA
7 x red, 6 x green, 6 x blue
so: most laptop power supplies are between 18V and 24V, and between 2A and 3A. This will let you make a light with 12-20 LED's (using strings of 4, 5, 6 or 7 LED's). if you have a high-current supply, you can put strings in parallel also.
- if you are looking for a power supply specially for this project, ideal would be 24-25V supply with 3-4A per set of LED's. ie, 3-4A for 18 LED's, 6-8A for 36 LED's, etc. As designed the controller can handle up to 15A maximum.
- the reason to prefer a supply between 20-25V that the controller will be a bit more efficient than with a 12V supply, and the maximum number of LED's you can power will be more. however if you want a smaller light, a 12V supply will be just fine. you can't use more than 25V, that is the limit for the regulator chips we are using.
Step 4: Selecting the LED's
I am using the Philips Luxeon LED's. Currently they are the most widely available power LED's at the lowest price (about $3 for both 1-watt and 3-watt stars). the place to buy these is direct from the distributor: http://www.lumiledsfuture.com (same as http://www.futurecb.com) - everyone else sells them at a huge markup. Undoubtedly other brands will become more available in the future.
The Luxeon LED's are available in a couple of formats - the most useful is the "star" format which has the LED already attached to a small heatsink. this is far easier to work with than the bare LED.
The Luxeon LED's come in both "1 watt" and "3 watt" stars. the difference between these is actually a lot less than the names indicate and they are priced nearly the same also (about $3 each). in reality, my tests show that with a large heatsink the "1 watt" model is capable of 3 watts output, while the "3 watt" model is capable of 4 watts. the "1 watt" model is notably very conservatively rated, it is really more like a 2-watt LED. the caveat is: the LED's efficiency drops with increased power (2 watts gets you about 65% of the light output of 4 watts), and lifetime may also be reduced (they are rated at 50,000 hours though). so if you are making a light for occasional use and want maximum output for the $$$, feel free to run the LED's considerably over spec. if you want an efficient room light for long-term use, stick to 2 watts on the 1 watt model, and 3 watts on the 3 watt model.
the other important difference between the 1 watt and 3 watt stars is that the 1's have an insulated heatsink, while the 3's do not - that makes the 1's a little easier to work with since you can mount them directly to a heatsink. the 3's require using an electrically insulating film between the star and the heatsink. (see the step on heatsinks).
- do you want a spotlight or a room light? if you want a room light, get the "batwing" or "lambertian" LED's. these shine light over a wide angle (either 110 degrees or 180 degrees).
- if you want a spotlight, you can get the "Star/O" model which has a built-in lens. or you can get the regular batwing model and buy a separate lens for it which easily glues on. There are several companies making very inexpensive ($1) lenses for the Luxeon that let you make a 5, 15, or 25 degree angle spotlight. I've used these ones: L2Optics/Dialight part numbers OP-005, OP-015, OP-025, and lens holder OH-ES1 or OH-S35. Try this: direct search at Future.
- equalizing brightness/hue: the different color led's are not all equally bright at full power. the simplest light (shown in this project) uses one string of LED's in each color, so when you turn all three colors on full power, the overall hue is yellowish (*very* warm). that's because the blue led's are not as bright as the other two. so if you are building a larger light, consider using an un-equal number of strings of the different colors. if you use the Luxeon-1's, try 2 strings of blue for each string of green and red. with luxeon-3's, equalized-brightness requires using 4 strings of blue, 2 strings of green, 1 string of red. this is only important if you are mostly using this as a white/off-white lamp. if you are using it for an FX lamp, there is not much point to equalizing the brightnesses.
what I used:
I used 1-watt star LED's for my light (running them at about 2.5 watts each) because I had a bunch of them already, i'd recommend using the 3-watt stars if you are buying new ones since they cost nearly the same. i used 5 red, 5 green, 5 blue led's. part numbers:
1-watt: LXHL-MDAC, LXHL-MM1C, LXHL-MB1C.
3-watt: LXHL-LD3C, LXHL-LM3C, LXHL-LB3C
more information: the manufacturer datasheets:
Phillips Luxeon Star LED's: http://www.luxeon.com/pdfs/DS23.PDF , http://www.luxeon.com/pdfs/DS46.PDF
L2Optics/Dialight Lenses: http://www.l2optics.com/luxeon.aspx
Step 5: Heatsink Selection
a lot of power goes into those LED's when they are running - 40 or 50 watts for my 15-LED lamp. unlike an incandescent bulb, we can't let the LED's glow red hot or they will burn out. in fact, the core of the LED can't get much above 100 degrees C before they will break! on top of that, LED's are less efficient the hotter they get. all this means we need a way to keep them cool. this is where a heatsink comes in. the heatsink is just a big piece of metal that conducts heat away from the LED's and into the air, by convection.
all the LED's will need to be attached to a heatsink in order to run at full brightness. in fact, without any heatsink at all the star-LED's can only run at about 2/3-watt each!
so a heatsink is just a piece of metal? YES! this is your opportunity for creativity and recycling. the heatsink will be large (much larger than you expect), so plan on it being the main structural element of your lamp. if your metal frame will be visible, you can use a piece of decoratively shaped metal.
- use a highly-conductive metal for your heatsink: aluminum, brass or copper. steel does not conduct heat very well - you can use it but you'll need a thick piece. scrap aluminum is easy to come by, and there are also many inexpensive sources for it at your local hardware store if you know where to look - rain gutters, various metal trims.
- how big a heatsink do you need? use this rule of thumb: minimum 10 square inches of exposed metal surface per watt of LED power. you can see in the photo that i used a piece of angle-bracket aluminum. my piece is 45 inches long, 1/8" thick, with 2" width on each side of the angle. that gives me an exposed surface of 45 x 2 x 2 x 2, or 360 square inches. count both sides of a sheet of metal only if both sides are exposed to the air. using this rule of thumb, your heatsink will run about 30 degrees C hotter than the surrounding air temperature at full power. keep in mind that the LED's internal temperature will be another 40-50C hotter than that. if you need a smaller heatsink, the only options are to use fins (which fit the same surface area into a smaller volume), or to use a fan. the rule of thumb here assumes "free air convection". if your heatsink will be in an enclosed space where the surrounding air will get hotter than 25C, then you need a bigger heatsink or a fan. advanced: try this handy calculator: http://www.frigprim.com/online/natconv_heatsink.html
with this calculator you can approximate most odd chunks of aluminum as a 2-fin heatsink with equal total surface area.
- how much is your LED power total? multiply: 3.8V per LED x LED current x number of LED's. for my lamp that's 3.8V x 0.8A x 15 = 46 watts, so i'm a little on the hot side.
- you need enough FLAT area on the heatsink to mount all the LED's. the mounting area must be perfectly flat to ensure good heat transfer between the LED and the heatsink. if your piece of metal is so thin that it can flex, then it will need some support or protection - you don't want an LED peeling off the heatsink under full power, it will burn out immediately.
Step 6: Circuit Operation
To help understand the component selection in the next step, lets first review the circuit and how it works. we'll also review the maximum limits of the controller.
the main component of the circuit is the voltage regulator (either LD1585CV or LM1084-ADJ, they are nearly identical in function). the voltage regulator is a 3-pin device that allows setting a fixed output voltage using two resistors. you can review the standard circuit on page 3 of the technical datasheet for the regulator.
but we want a variable output, controlled by a dial! so all we do is to replace one of the two resistors that sets the output voltage with a variable resistor, or potentiometer. actually though, we use a resistor and potentiometer in series, because we only want to adjust about 1/2 the voltage range. so in the circuit, R2, R4, and R1 are the resistors that set the regulator's output. the regulator output is approximately proportional to: (R2+R4) / R1. so with a fixed R1, we increase R4 to increase the output voltage, and decrease it to decrease the output voltage. in the next step we'll go into the details of selecting these values.
what else? we need a current limiter. this is an important feature for driving LED's. the current through an LED is very sensitive to the voltage - if you increase voltage across the LED, current can increase a lot. this makes it very easy to accidentally put too much current through the LED, which can either burn out the LED or the power supply.
another reason it is easy to put too much current through an LED is that the voltage drop of an LED goes down when the LED heats up. reducing the voltage drop means more current at the same voltage. and putting more current through it causes it to heat up more! this phenomenon is called: "thermal runaway", and it affects both LED's and transistors.
R3 and Q1 form the current limiter part of the circuit. how does it work? R3 is the "sense resistor". all the current through the LED's goes through the R3 also. the transistor Q1 will turn on when the voltage across R3 (which is proportional to the current through it) reaches about 0.55 volts. when Q1 starts to turn on, it will act like a new, small-valued resistor R2, and thus the output voltage of the regulator will be reduced. reduced output voltage will reduce the current through the LED's and R3, and the transistor Q1 will start to turn off. this is a "feedback loop", and it happens so rapidly as to create a smooth balance point right at the desired current limit. how do we choose our maximum LED current? by choosing the value of R3 that turns on Q1 when our maximum desired current is reached.
- what are the limits of the controller?
- the voltage regulator can handle up to 28V input, and 5 amps current (although you'll need a big heatsink on it to do that much current).
- the regulator will function below 5V input, so that's low enough that you could power just 1 LED if you wanted.
- this is a simple analog controller, so if you need a scientifically reproduceable color combination, this light isn't going to do it. in fact, using this controller the colors are going to shift a teeny bit as the lamp heats up, although once it is warm things should be pretty consistent.
- C1 and Q1 are not very particular. for C1, you need at least a 35V rated capacitor, with between 10uF and 100uF. for Q1, pretty much any NPN transistor will work, although the one i specified has more consistent thermal performance than most (which will keep your current limit setting closer to what you expected if the inside of the controller box heats up).
- there are a lot of other "linear voltage regulators" that could be used here, the ones i listed have the best overall combination of low cost, flexibility, efficiency and power handling.
Step 7: Selecting Resistors and Dials
the exact resistor values you use depend on the number and type of LED's and the power supply voltage.
Selecting R3 sense resistor
R3 is the "sense resistor" for the current-limiting circuit. select the value of R3 as follows: R3 = 0.55 / (LED string current). so for my circuit I have R3 = 0.55 / 0.8 = 0.69 ohms. resistors don't come in every possible value, the closest match was 0.68 ohms. you also need a resistor that can handle a bit of power, use this guideline:
LED string current:
less than 200mA: standard 1/4 watt resistor, search digikey for: "yageo CFR-25JB"
less than 1200mA: 2 watt resistor, search digikey for: "panasonic ERX-2SJR", they go down to 0.47 ohms.
1200mA to 5000mA: use a couple of 2-watt resistors in parallel, or else try: "huntington ALSR-5". (the limit for the voltage regulator we are using is 5 amps).
note that the current-limit is not especially accurate, using just the calculation it might be 15% off. if you need it more accurate, you will need to build your circuit and then test a couple of resistor values. note that the current limit will decrease as the temperature of Q1 goes up - that's a feature!
Selecting R4 control slider/dial
First choose if you want a slider or dial! this is your user interface for your controls. It's less work to make a control panel using dials, because you just drill a hole for them, but you might prefer the look & feel of the sliders. I went with the sliders, but you'll see how much of a hassle they were later. any dial or slider between 2k-ohm and 10k-ohm will work. a 2k-ohm is the best because it allows precise calculation of the output voltage without testing. for sliders, i was only able to find 10k-ohm sliders which required a bit of trial-and-error to get the output voltages correct.
Slider: search digikey for: "panasonic EWA-Q12C15B14", a 10k-ohm linear taper slider
Dial: search digikey for: "CTS 270x232a", a 2k-ohm to 10k-ohm linear taper dial w/o switch
Setting R1 and R2 control range resistors
The combination of R1, R2 and R4 set the output voltage (= LED brightness) of the regulator. the output voltage is approximately equal to: 1.25 * (1 + ((R2+R4) / R1)). This becomes less accurate with larger R values. With a 2.5k dial for R4, the formula will be very close, with a 10k dial, you'll need to hand-test your R1, R2 values. below i work through two examples: one with 10k slider and one with 2.5k dial.
We need high-precision resistors for R1 & R2 (that means 1% accuracy rather than the common 5% accuracy). Search digikey for: "yageo MFR-25FBF" which will show all the available values.
So how do we use that output voltage formula? we want to choose our values of R1 & R2 so that when the dial is all the way to the left the LED's are just turned off, and so that when the dial is all the way to the right the LED's are at maximum power. To do that we need to know the voltage across the LED's where they are just turned off, and the voltage across them at our maximum set current. You can refer to the LED spec sheets from the manufacturer, or to my Power LED Data Handy Reference Chart where i've listed some typical working values.
Example 1: R1 & R2
here's the calculation for my circuit using values from the 'handy chart' above.
for 5 x red LED, our "turn on" is at 5 x 1.8 = 9V, and maximum power is at 5 x 3.8 = 19V.
for 5 x green or blue, "turn on" is at 5 x 2.4 = 12V, maximum power at 5 x 3.8 = 19V
using the regulator's output voltage formula to calculate R1 and R4 for the red led's using my 10k-ohm slider (which is 0 ohms at turn-off and 10k-ohms at maximum power):
Vout = 1.25 * (1 + ((R4+R2) / R1))
9V = 1.25 * (1 + ((0 + R2) / R1))
19V = 1.25 * (1 + ((10,000 + R2) / R1))
solving the two equations gives:
R1 = 1250 ohm
R2 = 7750 ohm
using the 10k-ohm slider there is a bit of error in the calculation compared to practice, so experimentation led to using the following values: R1 = 1.2k-ohm, R2 = 6.8k-ohm with a tested output of 9V to 20V
similarly with the green and blue (using 12V and 19V in the equations):
R1 = 1790 ohm
R2 = 15360 ohm
and experimentation led to: R1 = 1.8k-ohm, R2 = 15k-ohm with tested output: 12V to 19.5V
my power supply is 19.5V, so this is a good setup.
- the current-limit circuit will kick in at about 800mA, or at about 3.8V per LED, so at around 19V per LED string.
- the controller + current-limit resistor will drop a minimum of about 1.5V, so maximum LED voltage is actually limited to about 18V (3.6V each), the last bit of the dial's range won't do anything, and with this setup i'm not likely to hit my current limit under normal conditions (but if something overheats, it will save the day)
- this circuit will work just as well for a power supply with more than 19.5V, you just burn more power in the controller.
- if you use different-length strings of LED's, or you have a different dial, you will need to recalculate the resistor values.
Example 2: R1 & R2
Here's a second example using a 2.5k dial and strings of 3 Luxeon-3 LED's. here, the R1 & R2 calculations should be "right on". For this example we'll target "full-power" to be the spec-sheet maximum for the Luxeon-3's, which is 1000mA for the green and blue and 1400mA for the red.
first we check my handy-chart or the led spec sheet to see the turn-on voltage for the different led's, and the voltage needed at the maximum current. for the red led's: 1.8V - 3.4V per LED is the target range (no current to max current), and for the green and blue we target 2.4V - 3.9V per LED
calculating R1 & R2 for the Red channel with 2500 ohm R2:
(1.8 * 3)V = 1.25 * (1 + ((0 + R2) / R1))
(3.4 * 3)V = 1.25 * (1 + ((2500 + R2) / R1))
R1 = 650 ohm
R2 = 2160 ohm
for the Green & Blue channel:
(2.4 * 3)V = 1.25 * (1 + ((0 + R2) / R1))
(3.9 * 3)V = 1.25 * (1 + ((2500 + R2) / R1))
R1 = 694 ohm
R2 = 3303 ohm
lastly, we should point out that with a regulated 12V supply, we won't actually get the green and blue led's all the way to full power because the controller will drop 1.5V minimum leaving 3.5V at most for each LED. what are our options?
- leave it, who cares.
- switch to strings of 2 LED's rather than strings of 3. the led's will work great although the controller will need a decent heat sink since it will burn a lot more power.
- most 12V 4-amp supplies are going to be the regulated type (any computer supply for example), but on the off chance you have an un-regulated supply (it will have a large heavy transformer), you are probably fine. most un-regulated supplies put out well over their rated voltage.
- if you are handy, many computer supplies have a "trim" knob inside them that lets the factory set the output at exactly 12V. usually you can adjust the trim knob to bump the output up to 12.5 or 13V. if the case of the supply opens up with screws, it probably has a trim knob.
- you could bypass the current-limiter in our circuit (replace R3 with a wire). this will reduce the controller loss to 1.0V, and get your blue and green to about 3.7V each. is it safe? if you are sure you have a regulated 12V supply - yes. at 3.7V you're still enough below the rated maximum for the LED that random variations should not be large enough to exceed the true maximum. just don't do this for the red channel!
Step 8: Attach LED's to the Heatsink
I used the 1-watt star LED's, these have an insulated backing plate so you just glue them straight onto the heatsink, no worries. if you are using 3-watt stars, you need an electrical insulator between them and the heat sink.
the "pro" way to attach components to a heatsink is: use thermal compound between the component and heatsink, add a special heatsink insulator layer if electrical insulation is needed, and screw down the component with nylon screws (or metal screws with a nylon bushing)
the "pro" way is a lot of work because you need to drill a lot of holes, and the special heatsink insulators are about $1 a square inch (let me know if you have a lower cost source!). luckily, the "pro" way is really a huge overkill here and we can do this much easier. why? the surface area of the luxeon star is large, and each LED is only about 3 watts. that's about 50 times less demanding thermally than a computer CPU.
so what's the easy way? we'll just glue down the stars using silicone glue. it works great. if you need a heatsink insulator, the best low-cost version of this is: thin mylar (polyester) film. most likely you already have some as reflective static-shielding bags, window-tinting film, or clear packing tape (although the glue on the tape is unsuitable, remove it with paint thinner). it is important to use mylar, other common plastic films will melt.
you need to use a flexible high-temperature glue, "GE Silicone-2" is ideal for this. press hard on the LED and squish it around a bit when you glue it down, you want as thin a layer of glue between the LED and the heatsink as possible & no air bubbles, to maximize thermal conduction. if you are using 3-watt stars, you need glue fully covering both sides of the insulator. use a little excess glue to make sure the entire contact area is glued (you can see where my glue is all around the sides of the LED after i squished down on the LED's).
- attach your LED's in groups of 3, each group has 1 red, 1 green, 1 blue LED. spread out the groups around the heatsink for best heat transfer.
Step 9: Wire the Led's
- use high-temp wire, rated for 90 degrees C at least. you don't want the insulation to melt by accident.
- i used 22 guage solid wire for the LED's. then at the end of the heatsink i connected that to 18 guage lamp cord for a 15-foot run to the control box.
Step 10: Start Stuffing the Circuit Board
the proto-board shown does not have any of the holes wired together, so to keep things simple we'll wire vertical columns together after the components are inserted. "better" proto boards already have the columns wired together, and that makes your life a lot easier if you have one of those. so here, anything we plan to wire together we'll put in the same vertical column of holes, and that way if you already have a proto board wire wired columns your circuit will look very similar.
- you will need about a 1" x 3" piece of proto-board minimum. mine is about 1" x 4", but i have quite a lot of empty space when i'm done.
- we'll be building 3 nearly-identical circuits. the only difference will be the R1 and R2 resistors.
- start by inserting and soldering VREG and Q1 into your proto-board.
- to identify the pins on the parts, look at the labeled front of the part with legs pointing down. pin 1 is on the left, pin 2 is the middle, pin 3 is on the right. look at the pins labeled in the schematic:
ADJ = pin 1
OUT = pin 2
IN = pin 3
E = pin 1
B = pin 2
C = pin 3
Step 11: Add the Rest of the Components
as shown, first I added R3 and R1, then i added C1, and last R2.
the leftmost circuit has the resistors for the Red channel, the middle and right are for Green and Blue.
Step 12: Finish Wiring the Controller Board
all that remains is to add connector wires to the controller, and to connect the component leads on the bottom of the board in vertical columns.
to create the vertical columns connections, strip your connector wires with a long section (1.5 inch) of exposed wire at the end. we'll bend that over and use it as the column wiring.
1) add the input positive and negative to the three circuits (red and black wires). i also added one additional capacitor between the input positive and negative.
2) add the wires that go to the R4 dial/slider (yellow wires)
3) add the wires that go to the LED's (green wires for plus, white for minus)
4) add wires for master input power: one red and one black at the right side of the board
Step 13: Build the User Control Panel
if you used dial controls, all you need to do is to drill 3 holes in your panel and screw in the dials.
for sliders, you have to make slots which is a bit tricky. here i used a pre-fab electrical junction box cover which had an appropriate sized cutout already. then i just needed to mount the sliders neatly in the cutout. i spaced the sliders apart evenly using some hex-nuts, and then put them on top of a rigid substrate (a re-cycled chunk of circuit board).
after lining everything up, i poured on some hot-melt glue (make SURE not to get any inside the sliders!). after the sliders were well attached to the rigid substrate, i aligned the substrate against the metal cover and glued them together.
we'll make the front pretty later.
Step 14: Connect the Control Panel to the Controller Circuit Board
1) the connections on the sliders are a bit delicate, so we need to protect them by strain relieving the yellow wires. first glue the yellow wires down near the slider.
2) then solder the yellow wires to the pins on the slider. my slider was rather confusingly marked, testing with my multimeter showed that i should connect to the two pins marked "1".
3) glue an 8-position terminal block to the back of the control panel
4) connect the remaining 8 wires - LED plus and minus, input power plus and minus - to one side of the terminal block. (all the remaining green, white, red and black wires)
Step 15: Put a Heatsink on the Voltage Regulators
the voltage regulators need a heatsink. the function of the regulator is to lower the voltage from the power supply to whatever the control knob indicates. the "dropped" voltage is burned up by the regulator and we need to get rid of the heat. this is the reason that the number of LED's in your strings needs to be close to the voltage of the power supply. if you used a 24V supply to power 1 LED, the regulator would need to drop 20V, or 80% of the power, and it would get very hot (and your setup would be very inefficient at making light). so we try to keep the voltage dropped by the regulator as low as possible - ideally, with the LED's at full power (about 3.8V per LED), we want the voltage on the LED string to be equal to the power supply voltage. in practice, the regulator has a minimum voltage drop (known as the "dropout"), of about 1 volt. on top of that, the current-limiter circuit drops 0.5 volt. so in practice we want the LED string at full power to be 1.5 to 2 volts below the power supply voltage, and this will result in maximum lighting efficiency and minimum heating of the regulator. conveniently, if the power supply is more than 5V above the LED string, we can just add another LED to the string, so this lets us get good efficiency for any power supply. overall, you will usually get 80-90% of input power to the LED's, and the controller will dissipate the remaining 10-20%. if you are building a 50-watt light like i am here, continue building as shown below. if you want your controller able to handle a full 360 watts of lights, you will need to put a heatsink on the regulators that can dissipate 50 watts.
- i didn't plan ahead! if i'd planned better, i would have been able to use my metal project box as the heatsink for the regulators. as it is, my circuit board sticks out past the side of the regulators so i can't attach them flat to the side of the project box.
- i'm using a chunk of the angle-aluminum for a heatsink, and i cut it so it would fit inside the project box. because of the convenience of using the project box as a heatsink, aluminum project boxes are ideal. as an alternative - if you have any old or broken computer power supplies around, these power supplies always have several heatsinks inside them which are the exact size for the regulators (TO-220 package) that we are using. even better, they will usually have heatsink insulators also.
- the metal tabs on the regulators are NOT electrically insulated. since we're connecting all three to a single heatsink, we need to insulate them electrically from the heatsink. you can find recycled heatsink insulators in an old computer power supply, or you can just use a piece of thin mylar (polyester) - refer to the LED mounting step for more details heatsink insulators.
- if you want to handle a full 300+ watt light, you'll need to use thermal compound here. you'll be putting up to 20 watts out of a single regulator. if you're only making a 50-100 watt light, just the silicone glue should be fine.
- using silicone glue: put glue on both sides of the insulator, and glue down the regulators. clamp them down until it is dry to ensure a good connection. after it is dry, also glue the heatsink directly to the circuit board so the assembly is rigid - you need to make sure the regulators can't pry themselves off the heatsink by accident.
- using thermal compound: drill holes in the heatsink to match the holes in the regulators. put thermal compound on both sides of the insulator. screw down the regulators using a nylon (insulating) screw, or else a metal screw with a nylon bushing around it (they are made specially for this purpose). see how much simpler it is to just use silicone glue?
- below i used the thermal-compound method.
Step 16: Connect External Wiring
1) install a strain relief in the side of your project box. electrical junction boxes are convenient because they are designed for this and you can buy strain reliefs sized just for the purpose. first pop out the correct sized hole in your junction box (this usually needs a hammer). then attach the strain relief to the hole.
2) feed the power cable and the 6 wires from the LED's through the strain relief, with about 6 inches inside the box. tighten down the strain relief to clamp the wires.
3) attach the wires to the terminal block. use a multimeter to check that you've connected the LED positives and negatives correctly.
4) before connecting the power cable, it is convenient to test the circuitry using your bench power supply. you can test safely by slowly increasing the input voltage with a 250mA current limit, to check for shorts, miswiring, etc.
5) if you are using a laptop power supply, note that these power cables usually are coax - the positive wire is in the core of the cable with an insulator around it, and the negative wire is all around the insulated positive wire. that makes it a little tricky to strip correctly.
Step 17: Assemble Project Box
- if you have a separate heatsink like me, fit the heatsink into the project box and screw it to the side of the box to get good heat transfer. you can't use a plastic box here! if your box was plastic the heat would be trapped inside until the box melted. it is surprising how little heat needs to be generated by the components to melt a closed plastic box.
- then just fit the top on the box, while keeping the wires neat inside the box (mostly - keep them away from the circuit to avoid bending stuff and allow good cooling)
Step 18: Put on a Pretty Face
now we'll clean up the front of the box. again, this is much easier if you use dials rather than sliders. there are a wide variety of knobs you can just buy that fit right onto your dials. there's probably existing knobs that will fit my slders too, but i couldn't find them so i made my own:
1) cut a dust cover for the sliders. i used a piece of black vinyl cloth, cut to shape with a knife.
2) glue the dust cover onto the face plate over the sliders
3) glue hex nuts to the ends of the slider knobs
4) glue colored plastic (or paint) the ends of the knobs
5) paint the rest of the metal face plate
Step 19: Power It Up, and Adding a Lampshade
if you are making a room light, you'll need some sort of lampshade. without a shade, the led's will be painfully bright to look at, plus they will create strange, color-offset shadows because the different LED colors are not right on top of each other. this is great for a dance party but otherwise really annoying. for my 4-foot long lamp frame, the cover from a fluorescent fixure makes a perfect shade - these covers are designed to have very high transparency (= low light loss) while scattering the light effectively. more typical lampshades from paper or translucent plastic will lose quite a lot of light, but will look very nice.
for a spot-light, glue the lenses on top of the LED's if you haven't already.
now power it up! what's your favorite new skin color?