Re: LED Brightness

[Andrew Stone]

Hi Phil,

First off, any small LED like this is essentially for "indication", not "illumination".  That's why little LED flashlights use 7-10 of them.  But even for "indication" they should be extremely bright if you look directly at one.

Check the current flowing through the LED by measuring it with a multimeter (on amps setting).  There are 2 possibilities; 1. The voltage you are providing is too low.  2. M5451 constant-current drivers are set too low.

Chances are the current is low since I don't ship the boards dialed all the way up.  To run everything full brightness, you need to understand a bit about how power is dissipated in an electric circuit.

Basically, all the power MUST be used somewhere.  So if it does not go into lighting your LED, it goes into heat.  So if you put 5v into the board and are driving a single 3v LED at 20mA, 2v*20mA*(number of LEDs) is dissipated as heat.  If you put 10v in, 8*20mA*(# LEDs) is (so 4 times as much).  Too much heat can destroy chips, so you need to minimize the heat and put it into the chips designed to take it.

On the top of the front face of your board you will see 3 tiny screw pots that can be turned with a #0 jeweller's screwdriver (available in a set for a few bucks at any hardware store).  These are single turn so a light touch is required.  The center pot will adjust the voltage (up to a bit below what you are putting into the board).  You want it to read about .7 to 1 volt higher then your LED's take.  So that's 4.2v for you.  But if your CAT5 runs are long, there might be some voltage loss in the wire... so a little higher might be needed.  If you set this too high, you'll put too much power into the M5451 chips and they will get hot and burn out.  Too low and your LEDs will be dim (or off).  But don't panic, nothing will happen immediately -- you'll feel the M5451's getting hot.  And also you can always experiment by having just a few LEDs on simultaneously.

Next the left and right pots adjust the current going through the LEDs (for the left and right IDE connectors).  You probably want to turn these until the power reads 15-19mA.  You won't be able to tell the difference between that and 20mA and your LEDs will last longer if they are run at a bit below their maximum.  The board increases the current to each LED by increasing the voltage up to the maximum you gave it via the center pot.  So if you are turning these and they max out at 10mA (further turning doesn't matter until you go past 0 and the current suddenly resets to 0) then you need to increase your voltage a bit.

Cheers!
Andrew

On Sun, Jan 22, 2012 at 11:58 PM, Phil Spitler <ph...@bonfirelabs.com> wrote:

Hi Andrew, I'm back to getting to work on my Lightuino project and have yet another question for you.

I am using the "all on" routine from your beginning PDE file. and the LED doesn't seem very bright, I am connecting it using the CAT5 breakout board (which I love) and using pin 36 to power them.

Is this something in the software or is it an issue with my LEDs. The ones I got are:

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=330577043870&ssPageName=ADME:L:OC:US:1123

It's not a problem if I need to but brighter ones, I just want to make sure I am getting the brightest possible that will work with this board.

Thanks again.

Phil

Phil Spitler |   Associate Creative Director  |  Bonfire  |  t : 415.394.8200  |  c : 415.571.3139  |  Bonfirelabs.com

[Phil Spitler]

I'm back to a single LED setup and dug up this email from a while ago.

I adjusted the center pot to about 4.2v then tweaked the left pot to about 15ma.

When I re-measured the voltage it seems to have dropped.

I think for the power I measure across the LED (parallel), for voltage can I do the same or should I put my meter in series?

Thanks.

[Phil Spitler]

It seems that I was wrong and I need to put the meter in series.

I followed this guide.

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_primer-multimeter.shtml

But when I try it, the LED doesn't light up and the current reading is tiny .004ma

Here are a few crappy photos to show the setup.

In the first one you will see the LED is on but there is no meter in the circuit.

The 2nd photo shows that I put the meter in the circuit but the LED is off.

sorry to be such a pain but I really don't want to burn out my Lightuino.

Thanks.

Phil

[Andrew Stone]

Hi Phil,

I couldn't tell from the photos where your meter was so did not reply.  But when you test current, you meter must be in series with the LED.  When you test voltage "across" a device, it must be in parallel.  When you power the board at 12v the "5VREG" chip (center of the board) will get a bit hot.  Its ok, since that chip is rated up to 125C.  But the 2 chips on either side (M5451) should not get burning hot.  Feel free to touch them with your finger while the board is running, but make sure you dissipate any static first.  In general the board is pretty robust against turning those pots -- especially when running just a few channels (during adjustments).  But connecting the 12.5v source to the LEDs might have hurt your board...only time will tell how serious the datasheet really is when it says "absolute maximum" :-).  If it did, its also possible that it hurt *just* the channels that you were using at 12.5v. 

Fooling with the left pot is more likely to burn out your LEDs...which is why you should definitely check the current with the meter for a long term installation.

Cheers!
Andrew

On Mon, Feb 27, 2012 at 12:59 AM, Phil Spitler <ph...@bonfirelabs.com> wrote:

Sorry to keep bugging you but I really don't want to screw up my board.

I just changed the center pot back, I had 2 LEDs connected in series and turned the pot until they both went out. Now when I connect just one, it is illuminating fine.

My fear is that I have changed the "left" pot when I was experimenting and I want to put it back but am unsure how how and where to measure the current.

With my single LED on, the board is getting hot very quick so I power it off in less than a minute.

I would love just a couple of quick notes from you to make sure I am putting my meter in the correct place to set up the board as you describe below.

I realize you are busy and have given me a ton of advice already. I feel like I'm really close but don't want to screw it up at this point.

Thanks.

Phil

Phil Spitler |   Associate Creative Director  |  Bonfire  |  t : 415.394.8200  |  c : 415.571.3139  |  Bonfirelabs.com

On Jan 23, 2012, at 6:14 AM, Andrew Stone wrote:

[Phil Spitler]

Thanks Andrew,

I didn't have the board connect when I tested the 3 LEDs and 12v, so I only killed the LEDs (phew).

I will check to see which components are getting hot, I can measure the temp with my meter and report back.

I will also double check the voltage across the LED and the current in series with the LED and report back.

Thanks again for helping out, your support is really helping me get past this stumbling block.

Cheers.

Phil

Phil Spitler |   Associate Creative Director  |  Bonfire  Labs  |  t : 415.394.8200  |  c : 415.571.3139  |  Bonfirelabs.com