Led Light Panel

Little background real quickly. I'm building a custom computer desk, everything will be mounted in the desk, all computer components, monitors, speakers, etc.

I'm designing the panel before I start the desk, so I know how much space I need on the location where the led panel will be mounted at.

I'm going to use 48 red, 48 green, and 48 blue pre-wired LED's with resistors, for 144 led's in total.

I going to build a led panel, with 3 potentiometers, so I can control the output of each color, RGB, so I can mix the colors, for whatever 100K's different color mixes, in theory anyways.

I would like to use the 12V outputs from one of the two power supplies that I will be using to power the computer and other components, though I have a feeling that the power supply may not be able to supply enough voltage and/or current to power the panel.

Power Supply Specs:
AC Input: 115V
DC output:
+3.3v - 24A
+5v - 28A
+12v - 70A
-12v - .08A
+5VSB - 3A
1000W max combined output

Specs located here:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?Sku=ULT40064

If someone doesn't think the power supply will work, just let me know, and I will be more than happy to change it to some other way, if you have another idea on how to power the circuit.

I have 4 banks with 36 led's per bank. Each bank has 3 rows of 12 led's per row. Each row will be wired in parallel, and each strip will be wired in series. Shown in attachments.

What I'm worried about is with all the resistors, some led's will be bright, and some will be dim. Though with me wiring them in parallel and then series they shouldn't dim (too much).

I'm going to use these pre wired led's with resistors, from here...
Blue LED: http://www.besthongkong.com/product_info.php?cPath=13_16&products_id=185
Red LED: http://www.besthongkong.com/product_info.php?cPath=13_16&products_id=147
Green LED: http://www.besthongkong.com/product_info.php?cPath=13_16&products_id=148

The values of the resistors are...
blue and green is 470Ω
red is 560Ω
(I can have them customized to whatever value I need, so that's good to know).

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I need to make sure that I have the potentiometer wired correctly, I haven't wired on in forever, so I'm a little rusty at best.

What should I use for the resistor values? I'm thinking that 560Ω, is a little too much, so I'm thinking about 120-240Ω for all resistors.

And should I use any voltage regulators, or similar, even though the power supply is producing 12V, give or take?

Read the article I'm writing, it may help.

http://forum.allaboutcircuits.com/showthread.php?t=18277

You should not put those LEDs in parallel without separate resistors, it is a potentially expensive mistake (which could take out a lot of LEDs).

PWM is not the only way, but you do need drivers for those pots as has been suggested. Lots of ways to accomplish this, which I suggest in the article. If after you read it and have specific questions feel free to ask.

I would love to see a photo of the project when you're done. Sounds cool.

Alberto said:

You will burn your potentiometer at the first trial.

48 leds in parallel (assuming 20 mA each) will draw ≈ 1 A. with a 500 ohms resistor in series you have 460 Watts of thermal power dissipated, enough to burn the most powerfull potentiometer.

You should use PWM for this project.

Alberto

Click to expand...

I was thinking about the potentiometer ratings, its been forever since I used one, or even seen one, lol.

I actually just finished doing the math, before I seen the replies.

Here is what I figured, (it was quick math, plus I'm a little rusty on ohms law!)

R=V/I
R=12v/2880mA (12v, 20mA for the led's (if the leds use 20mA)
240Ω=12v/2880mA (the current rating suprised me, 2.88A, at 12V)

OR

R=V/I
R=12/4320mA (12v, 30mA for the led's (if the leds use 30mA)
360Ω=12/4320mA

I'll have to check out PWM!? I've heard it before, but never used it.

Bill_Marsden said:

Read the article I'm writing, it may help.

http://forum.allaboutcircuits.com/sh...ad.php?t=18277

You should not put those LEDs in parallel without separate resistors, it is a potentially expensive mistake (which could take out a lot of LEDs).

PWM is not the only way, but you do need drivers for those pots as has been suggested. Lots of ways to accomplish this, which I suggest in the article. If after you read it and have specific questions feel free to ask.

Click to expand...

I'll have to read that post, I'm at work right now, so I don't REALLY have the time, we're just slow right now.

The led's that I'm buying, has resistors pre-wired in, and I can customize the resistor value, for free, so thats not a problem

BTW, You live in Dallas? I live near Ft. Worth, in a small town named Azle.

Omegadiver77 said:

I would love to see a photo of the project when you're done. Sounds cool.

Click to expand...

I'll be taking progress pictures over the process of designing the panel, and the desk, so no worries about the pictures.

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Due to me being at work, this post may not have the best wording, or fully understandable, I'll check it when I got home tonight, and make any changes, and post more about this project.

You forgot to plan your project then it will make lots of smoke.

A red LED is about 1.8V so with a 12V supply and a 560 ohm current-limiting resistor its current is only 18.2mA. The resistor dissipates and wastes 0.19W.

Your circuit should have 6 red LEDs in series and in series with a 62 ohm current-limiting resistor for 19.4mA and the 62 ohm resistor dissipates and wastes only 0.052W.

The other colour LEDs should also be in series and have their own current-limiting resistor.

100 years ago live theater used huge hot rheostats to dim lights on stage.
Today Pulse-Width-Modulation uses a little potentiometer and a high frequency switching circuit for cool dimming.

Audioguru said:

You forgot to plan your project then it will make lots of smoke.

A red LED is about 1.8V so with a 12V supply and a 560 ohm current-limiting resistor its current is only 18.2mA. The resistor dissipates and wastes 0.19W.

Your circuit should have 6 red LEDs in series and in series with a 62 ohm current-limiting resistor for 19.4mA and the 62 ohm resistor dissipates and wastes only 0.052W.

The other colour LEDs should also be in series and have their own current-limiting resistor.

100 years ago live theater used huge hot rheostats to dim lights on stage.
Today Pulse-Width-Modulation uses a little potentiometer and a high frequency switching circuit for cool dimming.

Click to expand...

Well its been several years since I've built a ciruit, so I'm quite rusty on it.

the leds I'm using already comes pre-wired with resistors, so the resistors aren't a problem. the leds are custom made to order.

I'm reading up onb PWM, I've heard of it before, but never knew what it was, so yeah, I'm still learning, give me some time.

I have full training in electronic technology, however that was 02-04, so its been awhile.

You might take a look at Big Clive's RGB LED controller and options, just to get ideas if nothing else.
http://bigclive.com/
He sells kits through his shop:
http://bigclive.com/shop.htm
Your project will be a lot more reliable if you use a PCB rather than lots of individually wired LEDs.

Keep in mind that you should position the LEDs so that they provide indirect light; you wouldn't want to have them in a position where the LEDs would shine directly in your eyes. Superbright LEDs are extremely bright nowadays, and they will damage your vision very rapidly if you look directly at them.

SgtWookie said:

You might take a look at Big Clive's RGB LED controller and options, just to get ideas if nothing else.
http://bigclive.com/
He sells kits through his shop:
http://bigclive.com/shop.htm
Your project will be a lot more reliable if you use a PCB rather than lots of individually wired LEDs.

Keep in mind that you should position the LEDs so that they provide indirect light; you wouldn't want to have them in a position where the LEDs would shine directly in your eyes. Superbright LEDs are extremely bright nowadays, and they will damage your vision very rapidly if you look directly at them.

Click to expand...

The leds will be shining down on the computer desk i'm building, I'll have to scan the picture or draw the desk in photoshop, to show the desk off, and the locations of the led panel.

thanks for the links, ill check them out!

Is your panel to supply illumination or direct viewing? a bright white LED is quite visable @ 1 mA., verry dim @ 1 μA..@ 20mA drove a CdS cell down to 50Ω, as did a slightly hazy sun.

Bernard said:

Is your panel to supply illumination or direct viewing? a bright white LED is quite visable @ 1 mA., verry dim @ 1 μA..@ 20mA drove a CdS cell down to 50Ω, as did a slightly hazy sun.

Click to expand...

somewhat both, but mainly just for illumination effects

My take: Three emitter-followers driving three groups of LED's, 16 strings of three for green, same for blue, 12 strings of 4 for red. Total load ,about 880 mA. Need better figures for V drop for ea. color. Simulated circuit using D1326 darlington tran. [ just becauce I had some ], 5 k pot., 10 Ω, & 11 V power supply. Used a 4 X 4.5 cm heat sink. Control smooth, heat sink slightly warm, resistor hot. Average 1 V drop of output to ct. of pot.

Actually this circuit is going to drop a minimum of 1.4V or more.



The LM2940-X is a better choice, since it drops a volt or less under load in close tolerance situations.

Truth, any voltage regulator will work, just adjust your current limiting resistor accordingly.

If you want to make a variable current regulator their are lots of ways to do that, but I get the impression you want a fixed amount of light.

Between this thread and the other one I'm having trouble keeping them straight. Their pretty similar.

http://forum.allaboutcircuits.com/showthread.php?t=18613

Bernard, check out Sziklai pairs. They offer some interesting alternatives to Darlington pairs.

well, I've decided that since using 144 leds are going to be a BIG PITA, I've decided to use 2-3 pairs of 1-watt high-power leds.

Before I start design the schematic and circuit, I want to get a few questions out of the way...

1) What would the best high-power led that I should go with, for a spot light effect.

2) I'm not quite sure, I don't know much about them yet.

3) What is the difference between 'batwing' and 'lambertian' led radiation pattern?

I know that with all high-power leds, I'm going to need a good heat sink, which is no problem. I got multiple chooses, that I have laying around, which includes...
*old P1/2 CPU heat sinks, their hiding in my bedroom somewhere
*well thats all I can think of right now.

For the wiring, I've got more than enough wire, I could probably wire an entire house with what I've got. I've got 1000 ft in 16 gauge alone

I've attached 2 images

1)desk drawing, I know its a little weird, but I'm not very good at drawing,

2)schematic of the wiring for one series of the high-power leds. Its not complete as you can see, I don't have any of the values for anything yet. There will be three nearly identical circuits, the only differences will be r3 for the current limit resistor.

Until I can get more info about the leds, I can't continue the schematic design. I'm using it as a basic guide line, atleast its a start.

I'm sure that I left something out, that I needed to ask or say, but its 3am I'm hungry and tired, so forgive me!

Check All Electronics, " 1 WATT, ULTRA-ULTRA BRIGHT LED" Cat# LED-109 Red; Cat# LED 111 Green; Cat# LED-112 Blue ; Cat# LED 110 has data sheet for all on web site. $8, 11.5, 11.50. www.allelectronics.com
These are Cree XLamp[tm] 7090

Bernard said:

Check All Electronics, " 1 WATT, ULTRA-ULTRA BRIGHT LED" Cat# LED-109 Red; Cat# LED 111 Green; Cat# LED-112 Blue ; Cat# LED 110 has data sheet for all on web site. $8, 11.5, 11.50. www.allelectronics.com
These are Cree XLamp[tm] 7090

Click to expand...

I use allelectronics all the time cant believe i forgot about them. Those are exctly what i need. Thank you

ok so I'm working on figuring out what my current limit resistor, here's what I've got so far, (I'm not the greatest in math, so work with me a little please)

Led's are 350mA each. I will have 3 per color, RGB.

Finding total current:
350*3=1050mA (1.05A for a string of 3 in series)

if power supply is 12v:

R=V/I
R=12/1050
87.5Ω=12/1050

OR

if power supply is 24v (same figures, except for V and R):

R=V/I
R=24/1050
43.75Ω=24/1050

So if I use a 12 volt supply, I should try to find a resistor that is around 87.50Ω in a 2-5 watt resistor, would that work for what I'm looking for?

I have a feeling that the heat output on the resistor will be crazy high, and a heat sink for a resistor will be in play.

I would like to stay with a 12 volt power supply, since I can just "tap" into the computer power supply, or should be able to.

I'm I even doing the math right, I've got the flu, and I'm all drugged up on flu medicine and nyquil.

Quick edit:
Does anyone know where I can get a '4-pin male molex' connector at with the pins?

Are you wanting to vary the intensity much? If so PWM is the way to go. If not a transistor current regulator would be the ticket, since they use so little voltage regulating the current. The advantage (dubious, but there) is that you can get heat sinks for transistors, and more importantly, transistors that are designed to be heat sinked.

here is a link of what I'm wanting to do, but I'm changing it alittle bit, instead of using sliders, I'm using potentiometer's, and instead of 5 sets of leds, I'm using only 3...

http://www.instructables.com/id/RGB-Color-Controllable-High-Power-LED-Room-%2B-Spot-/

read some of that, and you will see what I'm trying to do.

sorry for all the edits, like i said, i'm pretty drugged up right now

the heat sinks won't be a problem for me, I have tons of old Pentium 1-4 heat sink/fan combo thats aluminum and copper, scrap sheets of aluminum, and some newer processor heat sink/fan combo.

Actually 1 ma is not that bright. It is visable, but as a display (and not that great).

Here is something I drew out, it combines PWM with current regulators. You can get 3.6Ω ¼W off the shelf, put two in parallel and you have your current limiting resistors.



It goes to 350ma per chain, each resistor (R4-R6) has ¼W disappation, and the resistor/transistor drops around 0.8V for each leg, leaving 11.2V for the LEDs. Not sure what the PWM range is, 20% to 80%? It can be increased by reducing R2, say 10Ω or so. Do NOT use Darlington's for this.

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Thinking about it, this could be a bit underdesigned. If the basic concept looks good I'll rework it, but the 1/3 of an amp through each transistor will get toasty.

I think Crazy wanted individual control of each string so 3 PWM ckts. needed. Cree plots blue & green to 500 mA @ 3.6V[700mA max]. 3 @ 3.6V= 10.8V; not much head room @ 12V , so maybe 15V @ 1.5A would be about right? Red 2.3V @ 350 mA. I'd still go with 1 pot & 1 transistor / string. R then: 15V-1.5V-[3.6x3] = 2.7V, 2.7/.5A= 5.4Ω, for blue & green @ 1.5W. Red R= 19Ω @ 2.5W.