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I have an array of LED clusters for a big VU meter. How can I distribute power evenly? Answered

Each cluster consists of 6 LED's, and is controlled individualy by an arduino (through a transistor).

If I start with normal power, when more LED's light up, they all dim. If I start with extra power, the first few LED clusters blow.

I don't want to have a separate power source for each cluster (there are 15)

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simmunityBest Answer (author)2011-07-28

I came across this and hope I am not too late to have relevant comments.
I've build several LED drive boards and know Microhip PIC's really well and arduino IO pins are similarly limited.

I am assuming you are using the arduino IO pins to directly switch the ground of the LED on and off. If you are switching the positive, that is not recommended as the power pin of the arduino cannot provide enough power to all the LEDs simultaneously unless you greatly limit how much current each LED draws and that would probably be dim and not to your liking. If you are switching the ground, that may work better but you still may be overloading the ground pins and drawing too much current through them as well. Increase the current limiting resistors resistance to lower the current and you may get an adequate result without resorting to ground switching FET's.

One thing is, you must follow the voltage and current limits provided by the manufacturer or the LED's will die prematurely. The dimming problem is not power supply voltage or current limit problems.

For high brightness, high current LED's you must add one FET to each ground side of each LED and use the arduino IO pind to switch the FET thereby eliminating the drain load on the arduino itself to just a few milliamps. I know this entails a lot more circuitry and soldering, but you will get constant brightness no matter how many LED's are on with FET drive. I've built such a board to multiplex many LED's using pchannel and nchannel FETS. The board worked okay, but I was not satisfied with the brightness when multiplexed.

One cheap and potentially easy solution is to use a lot of cheap PIC micro controllers each directly driving just one or two LED's and being controlled by a serial port from the arduino. If your LED's drive requirements are within the PIC's limits, this can be a way around using FETs but you have to program each PIC. They can run with minimal external components with internal RC oscillators, but this may be beyond your programming and circuit design skill at the moment.

Have fun and good luck

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iceng (author)2011-07-28

As a hardware / software tech geek myself, I'm confident you simmunity are aware that sometimes we parallel two or three uP pins to drive a single LED for the extra current.
There are instructions that can simultaneously toggle the paralleled pins,
if they are selected with understanding of the micro.

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simmunity (author)iceng2011-07-29

iceng, the use of two IO pins in parallel has merit, but the real problem is not enough ground pins on the chip itself. The bigger PIC's and other part often have a 2 or more but even then, those can be overloaded. What is worse about overloading the parts ground or power pins is the supply to the chip itself become unstable based on the external load and causes the part to run out of spec sporadically and possibly crash.

I found a very nice premade solution to the LED drive problem at:
https://www.instructables.com/id/24-Channel-USB-Connected-LED-Controller-upto-1A-p/
This is well designed hardware kit capable of dealing with RGB common anode or cathode (during transistor installation) and can drive most LED's. It is USB driven but can be programmed with PIC dev tools. I like the CCS compiler myself but there are many ways to program a PIC...
Anyone looking to control a bunch of LED's should look at this kit or at least use pieces of the schematic and parts to create a solid solution.

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iceng (author)simmunity2011-07-29

I play with bigger uPs where that can suck 20ma per pin up to 120ma per chip and then move to Fets or the octal ULN280x series with built-in reactive diodes good for inductive loads :-Þ.......

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Stuffses (author)2011-06-09

So, the problems were:

-wrong resistors
-wiring problem
-I didnt know that "No, if they have limiting resistors TO EACH ONE they will take what they "need" and no more."


So, everything is working now.

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steveastrouk (author)2011-06-09

Do you HAVE resistors ?

You said in the original question that "the first few LED clusters blow"

Without resistor, a.) They WILL blow and b.) The PSU, supplying far more current than it should do will limit, and the other LEDs will dim.....

Steve

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Stuffses (author)steveastrouk2011-06-09
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steveastrouk (author)Stuffses2011-06-09

Where does the "blow up" come from then ? Can you post a schematic ?

Steve

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Stuffses (author)steveastrouk2011-06-09

I mean, if there is enough power to turn on all the leds, when only one or two light up., they will receive all the power, and blow up.

I need a way to regulate the power to each LED

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steveastrouk (author)Stuffses2011-06-09

No, if they have limiting resistors TO EACH ONE they will take what they "need" and no more. I suspect you have a design issue. Post a schematic ?

Steve

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Stuffses (author)steveastrouk2011-06-09

OOOOHH. ok, I think I was just using the wrong resistors. I`ll check back when I fix it

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iceng (author)Stuffses2011-06-09

So it's a no,  to Post a circuit diagram ?

A

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Stuffses (author)iceng2011-06-09

No, it worked fine, and lights up my whole room with pretty lights!

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rickharris (author)2011-06-09

Much easier and possibly cheaper to use a dedicated VU meter ic - readily available. eg LM 3916

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7654321 (author)2011-06-08

If you have resistors going to each LED you shouldnt be blowing them up.

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Stuffses (author)76543212011-06-08

No, thats not the problem. Its that the LED's dim when more are turned on (they all use the same power supply). So adding resistors wouldn't fix that (I think).

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