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Using Arduino => Project Guidance => Topic started by: charliehorse55 on Mar 02, 2011, 03:18 am

Title: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 02, 2011, 03:18 am
I'm working on some new stage lights for my high school. The budget for this project is ~$300.

So far I have planned this:

10W RGB LEDs (350mA/10V per color channel) x8 - http://www.dealextreme.com/p/10w-500-lumen-multi-color-rgb-led-emitter-metal-plate-60-70-degree-44042 (http://www.dealextreme.com/p/10w-500-lumen-multi-color-rgb-led-emitter-metal-plate-60-70-degree-44042)

120W Computer Powersupply at 24V for powering LED drivers http://www.dealextreme.com/p/120w-universal-laptop-power-supply-15v-24v-dc-output-100-240v-ac-15647 (http://www.dealextreme.com/p/120w-universal-laptop-power-supply-15v-24v-dc-output-100-240v-ac-15647)

Arduino PWM outputs for control - the 6 outputs will be mapped to R/G/B for stage left and stage right to allow for advanced color mixing.

Buck Constant Current 1A with PWM Controller - http://www.newark.com/national-semiconductor/lm3401mm-nopb/ic-pfet-controller-buck-msop-8/dp/54M4678 (http://www.newark.com/national-semiconductor/lm3401mm-nopb/ic-pfet-controller-buck-msop-8/dp/54M4678)  - 6 of these - 1 per PWM channel

Run 4 light channels from each driver in 2 series 2 parallel. (for 20V/700ma)

Questions I still have:

1) How to solder that chip? It's 3x3mm and I have no idea how to solder up 8 wires to it. Maybe there is a chip socket for that shape of chip (hopefully)

2) Housing/Reflectors for the LEDs. I can see a couple other LEDs of the exact same dimensions but different colors/intensities so I have a feeling that is a standard LED form factor. Anyone know of housing for it? Looking for roughly a 12-15 degree beam angle.

3) Is it a bad idea to run multiple strings of LEDs in parallel? Will this cause a load imbalance?

Finally, if you see another problem with something in my plan please don't hesitate to help! Thank you in advance.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: abrookfield on Mar 03, 2011, 02:27 am
http://www.newark.com/roth-elektronik/re903/smd-adapter/dp/24M6865?in_merch=true&MER=ACC_N_L5_SemiconductorsIntegratedCircuits_None
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: MarkT on Mar 03, 2011, 04:14 am


http://www.newark.com/roth-elektronik/re903/smd-adapter/dp/24M6865?in_merch=true&MER=ACC_N_L5_SemiconductorsIntegratedCircuits_None

NO!! This is a 10 watt LED - it has to be mounted on a substantial aluminium or copper heatsink and may require a fan too.

1)  Soldering to it may be a little tricky - the lead pitch may fit stripboard though?

2)  I know some of the 3W and 5W LED packages have reflectors available - you'll have to search - but it may be that there's too much heat and a plastic reflector just melts.

3) If the LEDs are matched (from same batch) you may get away with it.  Given the high power there will be thermal imbalances that upset things - best to have some current balancing resistance for this reason alone.   Note that each colour has a different forward voltage so you can only common the reds, the greens and the blues independently.  Its important that there is good heatsinking so the different LEDs are at similar die temperatures to help with balance - and ensure long life.

[You also need to know that these devices can damage your eyesight if you don't respect them]


Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 03, 2011, 05:27 am
Aren't the LEDs already mounted on a plate with leads sticking out to the sides?

From the picture it looks like 3 die wired in series,  with an anode connection on side and a cathode on the other.

I would run 2 of these in series, each one dropping 10-11V and sharing the 350mA of current. Will need a current limit resistor and a MOSFET to  switch the current.
With 4 pair, you only 4x350mA  x 3 colors max.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 05:58 am
Thanks for all the help so far!

I was planning on running only the same color on each driver, as I want separate PWM control for each color so that I can mix the colors and create anything in the rainbow. Basically the PWM will control the brightness for the Red, Green and Blue channels separately, with one set for the left of the stage and the other set for stage right. This will utilize all 6 of the Arduino's PWM channels perfectly. 

I found a larger driver IC that has much, much larger pins that will be about 100x easier to solder. Additionally, it already has the necessary capacitors/resistors inside of it so the wiring becomes as simple as wiring up + and - for the power input and the LED, and a 5th pin for control.

My new problem is that the driver IC wants a PWM signal with an amplitude of 1.25V maximum. The Arduino outputs a 5V signal. I want to put a resistor in there to drop the voltage but I don't know what current the arduino PWM signal usually pushes. (or is there a better way to reduce the amplitude of the PWM signal?)

As for cooling these LEDs will be screwed to a large aluminum bar with a dab of thermal paste in between. The aluminum bar will have some fins on the back and a small cooling fan blowing over them. The thermal conductance of the aluminum is pretty high and the LEDs will only be a couple of inches apart so they should stay with a few C in temperature of each other.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 03, 2011, 06:03 am
Here's a circuit I would recommend if my assumptions about the modules are correct.
Maybe a little overboard with the fuses, but you've got high voltage, better safe than sorry.
I set it up for left & right lights, if you want 4 seperate setsof lights just add more MOSFET drivers.
Maybe use a MEGA vs an UNO to have PWM lines built in.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 03, 2011, 06:05 am
Post a link for this new driver chip. I think 6 MOSFETS in TO-220 packages are all you really need.
The Newark link is down at the moment for the original device.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 06:12 am
It's the LDU2430S1000-WD from XP Power.

http://www.xppower.com/orderPriceList2.php?seriesid=100556&lang=EN

Comes pre-wired :D.

Looking at your circuit (thanks), it appear the LEDs are driven by a voltage source and a resistor, with no control other than the PWM signal? I need to get exact light levels to get accurate color mixing and similar current flow though all LED modules to insure even brightness.

Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 03, 2011, 06:21 am
"Looking at your circuit (thanks), it appear the LEDs are driven by a voltage source and a resistor, with no control other than the PWM signal?"
That is correct.
Light levels will set by the 255 levels of PWM available to you from the arduino.
analogWrite(Ax, 0) will be full off,
analogWrite(Ax, 255) will be full on.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 06:30 am
I understand that, but how equal will the current in the LEDs be? For example when the arduino is set to 255 across the board all of the LEDs should have 350mA +/- 10mA running across them. If one LED had more current than the other it could be counter acted in software with scaled PWM values but it'd be better to have a more even output precisely controlled by a driver IC.

Basically, if I set the red channel on the left and right to be 100% brightness, all of the RED diodes should be emitting the same amount of light. I just do not know how close you can get to a perfect even brightness with resistors. If one LED got more current the left side of the stage would appear more bright than the other.

Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 03, 2011, 04:01 pm
As drawn up, there are 12 LEDs of the same color on each side. There may be some small variation from part to part. The variations will pretty much be a wash among part. If you find one side is too bright, bring down the PWM on that side a few notches.
If you use current limiting resistors that are 1% variation, then  350 +/- 10 should be achievable.
I would suggest reading the value of a potentiometer for each color, and using that to control the PWM value that is used. Then you turn a knob and see the lights of up & down.
You can also create presets. Twiddle the knob to find the color you want with the cast & set in place, then program a button to jump (or fade up to) those colors when the button is pushed.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 04:40 pm
Ah, I see thanks. I think I'll use a bunch of trimpots inside the unit for control. I had planned on adding presets in the software, including the ability to read a light program from a file.

The only concern I have now is the wattage of those resistors. The voltage of the red channel is much less than of the the other two, and thus in series you get:

Red: 14-16V
Blue: 20-22V
Green: 20-22V

Now, at 350mA the resistor will have to drop 8V, so that gives:

0.350*8V = 2.8W. For safety I want a 5W trimpot, which could require a heat sink and such. Unless I am misunderstanding how this setup is supposed to work?
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: Grumpy_Mike on Mar 03, 2011, 04:48 pm
Quote
I want a 5W trimpot

Not sure if such a thing exists. These are normally quarter watt. That is why constant current drivers are such a good idea.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 04:56 pm

Quote
I want a 5W trimpot

Not sure if such a thing exists. These are normally quarter watt. That is why constant current drivers are such a good idea.


That's what I suspected. I guess I'll be sticking with the constant current drivers then. I will need some small trimpots to balance the current between the two series of LEDs but they won't be dissipating much heat at all.

Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 09:34 pm
Got most of the project worked out quite well now.

Just need to figure out how to turn the 5V amplitude on the arduino's PWM signal to the 1V amplitude required for the Driver IC's I have.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 03, 2011, 10:05 pm
Run it thru a voltage divider.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 03, 2011, 11:00 pm
Thanks for that diagram Crossroads, that explained it perfectly.

Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: cverink on Mar 04, 2011, 11:53 pm
User KE7GKP is correct.

According to the datasheet you linked to, the Dimming input pin, Pin#2 "Can be connected to a logic level PWM signal". (Typical logic levels are 3.3V or 5V)

On page 3 it says Vdim threshold ranges from 1.85 to 2.25 typically 2. Therefore when the voltage is below 1.85v it is off and when it is above 2.25v it is on (or vise-versa). This confirms you can use either a 3.3V logic or 5V logic. So the arduino output will be fine. No voltage divider is required.

Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 05, 2011, 04:38 am

User KE7GKP is correct.

According to the datasheet you linked to, the Dimming input pin, Pin#2 "Can be connected to a logic level PWM signal". (Typical logic levels are 3.3V or 5V)

On page 3 it says Vdim threshold ranges from 1.85 to 2.25 typically 2. Therefore when the voltage is below 1.85v it is off and when it is above 2.25v it is on (or vise-versa). This confirms you can use either a 3.3V logic or 5V logic. So the arduino output will be fine. No voltage divider is required.




No, I was asking about the data sheet I linked later on in the thread, for a different product. It clearly states that the maximum Vdim voltage is 1.25 and that a PWM signal should be 0-1V amplitude.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 05, 2011, 04:50 am
http://www.xppower.com/pdfs/SF_LDU.pdf
This one, showing 1.25V

PWM
Output Current Range • 25% to 100%
Operating Frequency • 1 kHz max
On Time • 200 ns min
Off Time • 200 ns min
Amplitude • 1.25 V max   <<<
DC Voltage Control
Output Current Range • 25% to 100%
Control Input • 0.3 to 1.25 V max   <<<
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 05, 2011, 05:54 am
The  LM3401 are only available in surface mount per that datasheet.
The  other part looks like a thru hole part it can be built up on a perfboard a lot easier.
(Still seems like overkill to me vs TO-220 transistors.)
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 05, 2011, 07:02 am
It is not easy to make switching LED driver working properly on protoboard. If you etch a PCB for it, it will be OK. I would suggest to check the pre-made modules as mentioned before. In theory, driving power LEDs in parallel is a bad idea. In practice, it may be OK as long as you use exact same LEDs. If one led goes bad for whatever reason, the other led in parallel will burn out instantly. I recently designed a shield for power led and wrote about my experiences. It may be useful for you. http://arduino.cc/forum/index.php/topic,51887.0.html (http://arduino.cc/forum/index.php/topic,51887.0.html)
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 05, 2011, 04:54 pm
YAY! Budget increase.

Now I have enough to manufacture my own PCB!

I won't be driving the LEDs in parallel anymore, I'm going to use 12x 500mA drivers at 350mA and then split the PWM signals from the arduino. I'm currently in the process of drawing up the circuit, I'll post it here when I am done.

EDIT: Is it okay to use a 350mA driver to drive 350mA? I know it's always a good idea to underrate electronics but I can't find a chip that does exactly what I need it to for with more current. I need an IC that can handle 24V input, 350mA output with a PWM frequency range that supports both the 500Hz and 1kHz speeds on the arduino pins.

It seems that the driver I listed in my original post is my best bet. Their datasheet seems to point to the fact that it was designed for use at 350mA.

Besides, this unit isn't going to see more than a thousand hours of use anyways. Not that I'd want to make it un-reliable, but if I reduce the IC'd MTBF to 40,000 hours from 80,000 it isn't a huge deal.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 05, 2011, 09:02 pm
Here is a tentative circuit representing one of the six color channels.

Will this work? I'm pretty sure it will but I want to make sure before I get to work designing a PCB.


Thanks.


(http://i56.tinypic.com/kf4cie.jpg)
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 06, 2011, 03:59 am
@neurostar: "In theory, driving power LEDs in parallel is a bad idea."  The design being worked from the first page of the thread had current limit resistors in each string, thus they are not actually in parallel.

@charliehorse,
This design is total overkil for a limited use stage lighting setup. Running left & right lights with brightness matching controlled by PWM adjust from ardiuno would have been plenty. Logic level mosfets with 0.005 Rds and 350mA going thru them would dissipate <2mW and would have no cooling needs.
Now you have a ton more parts to deal with, you've got a pile of NPN transistors that may need cooling as well, dissipating 250mW each, a controller that you are using at 100% capacity, no derating, and with 0.95mm lead spacing which will be a bear to solder hand.
http://www.onsemi.com/pub_link/Collateral/CAT4201-D.PDF
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 06, 2011, 05:51 am
If you still want to pursue something besides MOSFET switching, consider one of the parts in this flyer I just received via e-mail notice.
http://www.maxim-ic.com/design_guides/en/LED_LIGHTING_1.pdf
MAX16822 or MAX16832 for example.
Higher current flow, fewer parts, and with a student/school e-mail you are eligible for free samples.
www.maxim-ic.com
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 06, 2011, 07:44 am
Perhaps I am not fully understanding the mofset idea...


Looking at the circuit you posted earlier it looks as though when the PWM signal is ON, the LEDs are simply in run directly off 24V with only a resistor to reduce the voltage. If this is true, that resistor could be dissipating up to 10W when the circuit is on.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 06, 2011, 08:27 am
10W?
P=IV = .35 * (24V-14V) = 3.5W. So use 5W resistors. 10V/.35A = 28 ohm for Red,
(14 v worse case for Red)
4V/.35A = 68 ohm for blue/green. P=4*.35 = 1.4W, use 3W.

Depending on your PWM setting from Arduino, power dissipated will be 1/255 to 255/255 of that.
Or use a high wattage rheostat for even more fine tuning of the light levels
Say a 50 ohm resistor in series with 25 ohm 7.5W rheostat if you can find a place to get them  - digikey has the part numbers to look for.
I would go  with fixed resistors and PWM trimming, see how it works & add rheostats if its not quite what you want.
http://www.ohmite.com/catalog/pdf/rheostats_wirewound.pdf
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 06, 2011, 08:41 am
Check that part about 50 ohm & 25 ohm rheostat - make the fixed resistor the full value so that if  the rheostat is turned to 0 ohm and PWM is at 255 (full current) you don't smoke the LEDs.  Just add more resisitance on top to dim the overly bright side.
Digikey has 12.5W in 25, 50, 75 ohm. If you use 25 for Red and 75 for blue/green, install on the brighter side LEDs, that will let you tone down the current by half compared to the other side, perception of brightness is another matter.

$26 each, so I would try PWM adjustments before adding these. Just leave yourself room to adjust the circuit later.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RES50RE-ND
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 07, 2011, 04:50 am
I have a 10W RGB LED that you are trying to use. These are exact voltage drops of the LED.
Red : 6.39V
Green : 9.38V
Blue : 9.22V
All at 350mA

If you want to make your own LED driver, why don't you use my design which is exactly fit with what you want to do. I published all Eagle cad files. http://code.google.com/p/neuroelec/source/browse/#svn%2Ftrunk%2FHP_RGB_LED_Shield (http://code.google.com/p/neuroelec/source/browse/#svn%2Ftrunk%2FHP_RGB_LED_Shield) If you design switching power first time, there are a lot of things to think about it carefully. The LED driver part of my design will cost less than $30 for 3 channels. You will have very efficient drivers and easy of PWM control that are proven to work. I will send you exact manufacture part numbers and BOM, if you need them.  You will only need three drivers to drive 9x 10W RGB LED with 36V power supply such as this. http://www.powersupplydepot.com/productview.asp?product=16034+PS

If you don't want to or don't need to make your own driver, I would shamelessly recommend my RGB LED shield.
You can use rest of your budget for led heat sink and housing.

3 x RGB shields : $37 x 3 = $111 + $3 shipping
9 x 10W RGB LED : $11.49 x 9 = $103.41 free shipping
36V/4.2A Power = $40.75 + $11 shipping
Total: $268

4 x RGB shields : $37 x 4 = $148 + $3 shipping
8 x 10W RGB LED : $11.49 x 8 = $91.92 free shipping
24V/5A Power = $19.33 free shipping
Total: $264

Quote
@neurostar: "In theory, driving power LEDs in parallel is a bad idea."  The design being worked from the first page of the thread had current limit resistors in each string, thus they are not actually in parallel.


I was talking about his initial idea. Even though it is not ideal, in practice you can drive leds in parallel with same leds which is the case for his setup. I tried, it worked with +-5% current difference though.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 08, 2011, 02:11 am
Thanks for all the input.

As this is my third term project for my grade 12 I need a little more depth than simply buying a premade solution in order to get a good mark I will be designing my own custom PCB.  Since I will be designing the PCB anyways it's better to use an actual driver IC than mofset switching.

That Maxium IC you linked to looks like an excellent choice.

I have no experience soldering chips onto PCBs, I have mainly only used my soldering iron to fix broken cables and connect wiring between the parts in my computer. Is there a service where you can get the PCB prototyped and assembled? I would  think there is as it would be difficult if you wanted a complicated board with a lot of small ICs.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 08, 2011, 03:22 am
OK. that was it. I think you see all these drivers are basically very similar. Since designing is a part of your education, I would recommend chips from national semi or linear tech, simply because you have a tool to simulate your circuit with the chip. You can learn a lot by checking and poking signal here and there. Many of those signal are hard to measure even with good oscilloscope. Once you understand one chip, you will understand rest of them easily. Designing proper value of parts need some calculations. Write down all the equations you see from datasheets. Later you will also find all those equations are same regardless of manufactures. Start from a reference design such as evaluation kit of a chip. PCB design of switching power is also very important. Careful on the SW - diode - GND (input capacitor) which need to be short length. You want to have big GND pour bottom of those switching circuit to minimize EMI. Thermal vias around the chip is also critical. If you don't pay for your PCB, 4 layer PCB is also good idea. For current sensing resistor, check Kelvin trace.  That's what I can think of right now. I hope that helps little.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 08, 2011, 04:07 am
@charliehorse55,
Yes there are PCB prototype and assembly houses. I don't know if that would bust your budget.
You are in the US?
You could make  a call to www.moderndevice.com in RI, see if they'd do it for you.
I don't have any means to do surface mount either, I use thruhole for what I do and struggle  hand-soldering the occasional surface mount part on a DIP adapter (actually have my wife do it, she  has better eyes than I for the really small stuff). 0.05" spacing was not too hard to do. 0.025" (4 pins in normal DIP space of 0.1"!) was very difficult.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 08, 2011, 04:25 am
SMD soldering is not difficult at all, when you have a proper PCB footprint. All you need is good magnifier. You will be amazed with how good your hands are under magnifier or low-power microscope. Instead of making one big PCB for four drivers, make four pieces. Order 5-6 PCBs, there are almost no price differences. You have something to practice. If you are still not confident with SMD soldering, send them to me as long as you are in US. I'll reflow them for free.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 08, 2011, 04:54 am
me too? I just got a couple of MAX6921AUI with 0.025" spacing, thought I was getting MAX6921AWI with 0.05" spacing.
Need to get an adapter too.
Waiting for this to come from Thailand,
http://cgi.ebay.com/SMD-CONVERTER-ADAPTER-PCB-SOT-TO-MSOP-SIP-DIP-14_W0QQitemZ120628243230QQcategoryZ36327QQcmdZViewItemQQ_trksidZp3286.m7QQ_trkparmsZalgo%3DLVI%26itu%3DUCI%26otn%3D2%26po%3DLVI%26ps%3D63%26clkid%3D7581984690700539118
not seeing a 28 pin adapter on it.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 08, 2011, 05:06 am
Why not.. Once you get them, send me email. sooner is better.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 08, 2011, 05:17 am
Cool, thanks neurostar. Trying to find some adapter boards that aren't too expensive yet at the same time not wait a month for delivery from Thailand.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 08, 2011, 07:17 am

OK. that was it. I think you see all these drivers are basically very similar. Since designing is a part of your education, I would recommend chips from national semi or linear tech, simply because you have a tool to simulate your circuit with the chip. You can learn a lot by checking and poking signal here and there. Many of those signal are hard to measure even with good oscilloscope. Once you understand one chip, you will understand rest of them easily. Designing proper value of parts need some calculations. Write down all the equations you see from datasheets. Later you will also find all those equations are same regardless of manufactures. Start from a reference design such as evaluation kit of a chip. PCB design of switching power is also very important. Careful on the SW - diode - GND (input capacitor) which need to be short length. You want to have big GND pour bottom of those switching circuit to minimize EMI. Thermal vias around the chip is also critical. If you don't pay for your PCB, 4 layer PCB is also good idea. For current sensing resistor, check Kelvin trace.  That's what I can think of right now. I hope that helps little.


That's what I've been doing. Haven't been using the simulators though, just been using the reference PCB design and modifying it to my needs. I like you idea of 6 seperate PCBs, one for each PWM channel. It seems like a much nicer and neater idea.

I live in Canada but I think I will just use a PCB assembly service. While I want to keep costs down, the school recognizes that the professional equivalent of this lighting system would cost a lot of money so as long as I justify all of the costs there won't be a problem. A moderate budgetary increase to go with a PCB assembly service is easily worth saving the potential failure of the project if I have trouble with the soldering. Additionally, even if I did manage to solder the chips I am leaving to U of T Computer engineering next year and thus I won't be able to fix the board if a mistake in my soldering causes a short. Finally, if the school wants to expand the LED array it would be very easy for them to simply order another copy of my design from the supplier.

Any suggestions for a good Canadian PCB assembler?
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 08, 2011, 02:04 pm
Try posting the question as a new thread, maybe a fellow Canadian can offer a suggestion;  its bound to me missed buried 3 pages down in this thread.
Also try asking the folks at dipmicro.com, or solarbotics.com, see if they can do it or offer suggestions.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 13, 2011, 05:28 am
Switching plans again. I found this beauty of an LED driver:

http://www.newark.com/linear-technology/lt3496ife-pbf/ic-led-drvr-tssop28/dp/07P8434

Three individual 750mA PWM outputs.

I will construct one PCB per light, and then use a terminal block to split the PWM signal from the Arduino. That way, If the lighting array needs to be expanded you can simply add another board and wire it up.

I'll also be using 30W RGB LEDs, they take 28-33V in, so I will use a +36V PSU.

Thoughts?
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: CrossRoads on Mar 13, 2011, 06:58 am
The LEDs use 33V max, so you plan to use 36V? Seems like planned overstress to me. Something has to dissipate that extra voltage.

Pay attention on the recommendations for the unused channels also (for your future expansion).

Watch this in your PCB layout:
"The exposed pad on
the bottom of the package must be soldered to a ground
plane. This ground should then be connected to an internal
copper ground plane with thermal vias placed directly
under the package to spread out the heat dissipated by
the LT3496."
"The exposed pad of the package is the only GND terminal of
the IC and is important for thermal management of the
IC. Therefore, it is crucial to achieve a good electrical
and thermal contact between the exposed pad and the
ground plane of the board."
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 13, 2011, 10:06 am

Switching plans again. I found this beauty of an LED driver:

http://www.newark.com/linear-technology/lt3496ife-pbf/ic-led-drvr-tssop28/dp/07P8434

Three individual 750mA PWM outputs.

I will construct one PCB per light, and then use a terminal block to split the PWM signal from the Arduino. That way, If the lighting array needs to be expanded you can simply add another board and wire it up.

I'll also be using 30W RGB LEDs, they take 28-33V in, so I will use a +36V PSU.

Thoughts?


Obviously, you didn't read what I wrote carefully. LT3496 is the chip that I used in the high power RGB LED shield. Again, I already published the design of circuit. You can just use driver part of the shield. http://arduino.cc/forum/index.php/topic,51887.0.html (http://arduino.cc/forum/index.php/topic,51887.0.html). You can not hand-solder LT3496, it has to be reflow due to GND. You have to find someone can do it for you. If you make only three of the driver, total cost of whole thing (PCB, parts, and assembly) will be likely higher than cost of three shields.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 13, 2011, 08:44 pm
I did read what you posted quite carefully, I just didn't catch the exact chip name. I will be running 6x 30W LEDs from 6 separate PCBs.

Also, I want to design my own circuit as this is a school project and I need something for the teacher to mark.


Finally, your circuit did not implement the Open LED protection feature of the chip, which I will need with my setup as it is entirely possible that someone leaves an LED string un-attached.

Your circuit will help though, I will modify it to my needs.

Thanks.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 14, 2011, 12:10 am
Open LED protection is not necessary for buck design unless you want to arbitrarily limit the output voltage. It is over voltage protection(OVP) for boost and buck-boost design. Run the circuit from LTspice, you will understand what it does. 
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 14, 2011, 03:11 am
Thanks again. I thought that it didn't make sense for buck but thanks for confirming. Makes the circuit a little simpler.

EDIT: And what is the maximum input voltage for driver? A 48V input would work great for my needs.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 14, 2011, 03:55 am

EDIT: And what is the maximum input voltage for driver? A 48V input would work great for my needs.


As in data sheet PVIN max is 45V. If you use same power for VIN, you are limited to use 30V.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 14, 2011, 03:59 am
Okay, I guess I'm stuck with the slightly more expensive 36V/300W PSU.

I assume the actual driver IC doesn't use much power so I can simply use two 200m ohm resistors to make a voltage divider for it to run it off the +36V?

EDIT: That won't work, but possibly with higher ohm resistors? I doubt the IC draws more than 2-3W of power anyways.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 14, 2011, 04:50 am
There are reasons why people don't use a simple voltage divider as a voltage regulator. It is not matter of efficiency. If you use high ohm resistors to reduce the resistor power dissipation, there are high voltage drop across the resistor depending on current draw. When LT3496 draw varying current especially during PWM, you will have huge fluctuations on VIN.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 15, 2011, 07:55 pm
Right, so a 12V VRM is a better idea.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 15, 2011, 08:29 pm
Why 12v? You want to use as low as possible, If you are going to use switching voltage regulator. Linear voltage regulator won't work, because of high voltage difference between In and out. I think you can use 5V from Arduino, anyway you need to power Arduino with lower than 12V.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 15, 2011, 08:58 pm
I was going to power the arduino through the USB interface. The only thing I'm going to be doing is driving 6 PWM outputs and 6 digital outs, no LEDs or other devices. The 2.5W a USB connection can draw should be enough for that right?

Unless the driver IC uses <0.25W each, I won't be able to run them off the Arduino because I will be using 6-8 of them.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: neurostar on Mar 15, 2011, 09:03 pm
USB power may not enough. Computer USB supply normally 500mA max, and LT3496 need 80mA max based on my measurement. You can just buy 3.3 or 5V power adapter.
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 30, 2011, 07:34 pm
Okay, I have done a major re-work of my driver board.

I am going to use the same LT3496 driver, but in boost configuration so that I can use a +12V input. This will also negate the need for a separate 5V power supply as the LT3496 can be run from 12V without issue.

I have also decided to switch to an I2C interface. I'm trying to find a chip like the ATTINY85, but runs from 12V. If that's not possible I can always power the chip from the Arduino as it takes <3mA at full load, but it would be much neater and easier to use a chip that can be run from the main +12V connector (that comes from a computer powersupply).
Title: Re: Help making a high powered RGB Lighting system for my highschool
Post by: charliehorse55 on Mar 30, 2011, 11:12 pm
I have now figured out that I will need a 5V source for that ATTINY85 so I have decided to use the +5V rail from the powersupply and power each board with a molex connector.

Should I power the LT3496 with +12V or +5V? I have access to both on the board.

Also, is there a way to flash the board so that when it is not plugged into a computer it executes some simple code? I am going to attach some 10k pots to the analog inputs and I would like the board to automatically read those values and run the lights accordingly if no computer is plugged into to control them.