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Using Arduino => General Electronics => Topic started by: byteofthat on Jan 08, 2015, 11:31 pm

Title: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 08, 2015, 11:31 pm
Hello,

I had recently built a word clock for my girlfriend as a christmas present. Now that it has been on for a couple weeks, I am noticing that the wear of the LEDs is not uniform. Of course I would expect some uneven wear over time, but after 3 weeks I would think I should not be able to see any difference.

Here is an imgur album of the clock in question (with pictures of my circuit too):
http://imgur.com/a/OdOxl (http://imgur.com/a/OdOxl)

The phrase at the top "KLUKKAN ER" (the time is) is about half as bright now as the other words. Another word "MINUTUR" is on almost all the time, it is only off for 10 minutes of every hour.

All the words are connected to shift registers and transistor arrays, so they don't turn on immediately when the clock is plugged in. However, "KLUKKAN ER" is tried directly to 5V and GND (with a 220Ohm resistor attached to each LED). I do have a couple of decoupling capacitors on my board where my power comes in, I was hoping that would prevent such a thing. Have I damaged these LEDS since they are connected directly to the power supply?

Does anyone have any idea why this might be happening? Is there something I am missing? Possibly some more information I can provide you with?

Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ChilliTronix on Jan 08, 2015, 11:42 pm
Well, you have one resistor per LED so I can't think of a good reason for there being a problem...
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 08, 2015, 11:49 pm
Could a voltage spike situation when being plugged in be the problem? Would it damage the LEDs in such a fashion?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ChilliTronix on Jan 08, 2015, 11:52 pm
Could a voltage spike situation when being plugged in be the problem? Would it damage the LEDs in such a fashion?
No...

Is it only one bank of LEDs that is failing? The one connected to power directly (although via a 220 Ohm resistor)? If so is it connected to 5V or possibly higher?

How many LEDs are you running in total, and do they all go through the voltage regulator on the Arduino?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 09, 2015, 12:30 am
No...

Is it only one bank of LEDs that is failing? The one connected to power directly (although via a 220 Ohm resistor)? If so is it connected to 5V or possibly higher?

How many LEDs are you running in total, and do they all go through the voltage regulator on the Arduino?
It just seems to be the LEDs that make up "KLUKKAN ER". I have one LED for each letter in that phrase. Each LED is connected to the power source directly, and each has its own 220Ohm resistor.

None of the LEDs go through the voltage regulator on the arduino. I just use the arduino to drive the shift registers and transistors arrays. I use one pin per word on the transistors array to sink an entire word to ground.

The power source is a 5 volt power supply, and I have measured it a few times, it's 5 volts. I have the positive and negative leads soldered to my prototype board, and then I run my connections from there. I have a decoupling capacitor at this point.

Does this make sense?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ChilliTronix on Jan 09, 2015, 12:58 am
It does, but the only issue I can think of then is a dry joint in the circuit for that word.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 09, 2015, 01:06 am
It does, but the only issue I can think of then is a dry joint in the circuit for that word.
Hmm, well I will take a look, That would be quite odd if that was the case. I will come back with info as I have it!
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ChilliTronix on Jan 09, 2015, 01:22 am
Re melt the joints just in case. I can't think of another explanation at the moment.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 09, 2015, 02:52 am
Hmm, tried using alligator jumpers to see if it was a connection problem and no change at all. I am going to try swapping one of the bulbs and see if that changes anything. If I notice a difference, I am not sure what I will do from there, because I still won't understand the initial issue.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: DVDdoug on Jan 09, 2015, 03:19 am
Yeah...  I don't know what's going on, but LEDs don't normally wear out or deteriorate.

I work in electronics and I've seen bad LEDs from the factory, but I don't think I've EVER seen an LED die in the field or go dim after some time.   And of course, resistors don't go bad  or wear out either.    (If a resistor is burned-up, something else failed first or it was a bad circuit design.)
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 09, 2015, 08:12 am
Where did you source your LEDs from?
Cheap eBay stuff from the far east often comes out of the reject bin. It could be a badly doped batch you have.

Very nice work by the way.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: cjdelphi on Jan 09, 2015, 02:39 pm
I thought your clock looked familiar!  it is, I saw it on hackaday (I think).

if it's not a voltage spike, and it is only several rather than all, then maybe they were bad to begin with and by that I mean they're being driven too hard because they can't handle the current supplied...

Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: TomGeorge on Jan 10, 2015, 01:20 am
Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?
And spec of the LED's.

Thanks.. Tom....... :)
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Chagrin on Jan 10, 2015, 02:05 am
Simple troubleshooting step would be to swap around your darlington arrays and shift registers. Make sure they're seated properly as well; perhaps your girlfriend set the clock down too hard or the heat/cold from the sunny window caused them to work themselves out.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: dlloyd on Jan 10, 2015, 02:27 am
Regarding the RGB LED strip (WS2812B) in the clock, this link (https://www.pololu.com/product/2546) is a good reference - look at the warning section 1/2 way down the page.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 10, 2015, 02:16 pm
@Chagrin: The shift registers/transistor arrays wouldn't have anything to do with it, considering the effected LED's are not connected through them, but are connected directly to the power and ground.

Maybe @cjdelphi is correct. I replaced one LED, and it was back to normal brightness. I had then just changed them all out for the effected letters and it seems to be working. I am going to see what happens after it runs for a while. Hopefully it was just bad LEDs. Time well tell!

Thanks for all the advice, everyone.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ChilliTronix on Jan 10, 2015, 02:56 pm
Did you re melt the joints as a test first? If not then the problem could still have been a dry joint issue... though it would be odd if it affected all in one run of LEDs and not randomly across the board.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: MarkT on Jan 10, 2015, 04:04 pm
White LEDs fade with time, the datasheet for the particular device should be consulted.

White LEDs change colour balance too - the basic issue is that the fluorescent yellow
gel in front of the LED changes with time.  The LED is typically blue/indigo/UV and the
other colours are generated by fluorescence.  Its hard to engineer a fully stable fluorescent
dye - note that ambient daylight could be aging the dye more than the blue from the LED
itself even - only the manufacturer will have data on these processes as they are a property
of the dye.

The actual LED emitter itself can age too, but this is likely to be a smaller effect due to
crystalline semiconductors being more robust than organic dyestuffs.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 10, 2015, 05:40 pm
Did you re melt the joints as a test first? If not then the problem could still have been a dry joint issue... though it would be odd if it affected all in one run of LEDs and not randomly across the board.
I did with a couple of them, and nothing happened. I figured as much when I tried using alligator clips to see if a bad connection was the problem.

White LEDs fade with time, the datasheet for the particular device should be consulted.

White LEDs change colour balance too - the basic issue is that the fluorescent yellow
gel in front of the LED changes with time.  The LED is typically blue/indigo/UV and the
other colours are generated by fluorescence.  Its hard to engineer a fully stable fluorescent
dye - note that ambient daylight could be aging the dye more than the blue from the LED
itself even - only the manufacturer will have data on these processes as they are a property
of the dye.

The actual LED emitter itself can age too, but this is likely to be a smaller effect due to
crystalline semiconductors being more robust than organic dyestuffs.
I understand this, but it doesn't explain why they faded so fast in comparison to other lights on the clock that were on almost the same amount of time. The word "MINUTUR" was on 83% of the time "KLUKKAN ER" was. Considering the clock has been in operation for less than a month, after waiting for a week and not seeing the same behaviour in the word "MINUTUR", I found it unlikely that it was just a "wear and tear" issue.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ChilliTronix on Jan 10, 2015, 07:05 pm
I would be interested to see how it is in another month.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 10, 2015, 09:12 pm
@Chagrin: The shift registers/transistor arrays wouldn't have anything to do with it, considering the effected LED's are not connected through them, but are connected directly to the power and ground.
And a resistor I hope.

It needs to be a higher value resistor than that connected through the transistor because there is more voltage across those than the transistor ones.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 12, 2015, 01:17 pm
And a resistor I hope.

It needs to be a higher value resistor than that connected through the transistor because there is more voltage across those than the transistor ones.
Each LED has it's own 220Ohm resistor.

I would be interested to see how it is in another month.
The word 'MINÚTUR' gave out, it has now sunk in brightness. I wonder if I am simply running too my current through the LEDs? I would figure 220Ohms would be enough. At 5 volts that would be ~22mA, but assuming there has to be some voltage drop, it must be even less than that.

Any more ideas now that the effect seems to be spreading?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: dlloyd on Jan 12, 2015, 02:15 pm
Regarding reply#14:

Right at the power input of the led strip, what value of capacitor did you connect?
I would recommend anything from 220µF to 470µF.

Right at the led strip and connected in series with the data line, what value of resistor are you using?
I would recommend 220Ω, 270Ω or 330Ω.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 12, 2015, 02:48 pm
Regarding reply#14:

Right at the power input of the led strip, what value of capacitor did you connect?
I would recommend anything from 220µF to 470µF.

Right at the led strip and connected in series with the data line, what value of resistor are you using?
I would recommend 220Ω, 270Ω or 330Ω.
I am not having trouble with the LED strip.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 12, 2015, 04:00 pm
Any more ideas now that the effect seems to be spreading?
It will spread if something is wrong. Can you make sure you have a 220 R resistor and that the voltage is 5V.

You need to subtract the forward voltage of the LED. Being white it might be as much as 3V so with that resistor you would get (5-3)/220 = 9mA. That should be well withing the limits of an LED, unless they are faulty or as I said the resistor or voltage is wrong, measure both with your meter.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: dlloyd on Jan 12, 2015, 04:04 pm
Ahh, I originally stopped at the picture that mentioned "The RGB LEDs are a WS2812B strip".

Quote
I painted the back of this black, and at first it didn't wind up sticking too well or looking too good. It wound up working out though.
Note: Just to mention - some types of paint could be conductive or semi-conductive (however I don't think this is the issue).

Quote
And so begins the arduous process of gluing in all the LEDs. I ordered 150 of diffuse white LED lights on ebay for next to nothing.
Careful there are no shorts (it appears some resistors could be shorting out).
(http://i.imgur.com/PsqJw73.jpg)


MAIN PROBLEM:
It truly appears that the resistance code is red/red/black with black (multiplier) and brown (tolerance). If so, then these are 22Ω resistors and the excessive current will cause the LEDs to fail.
The first 3 colors should be red/red/brown for 220Ω. EDIT: (I see Grumpy_Mike is a bit quicker than I)

(http://i.imgur.com/cxBF1fJ.jpg)
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 12, 2015, 11:12 pm
It will spread if something is wrong. Can you make sure you have a 220 R resistor and that the voltage is 5V.

You need to subtract the forward voltage of the LED. Being white it might be as much as 3V so with that resistor you would get (5-3)/220 = 9mA. That should be well withing the limits of an LED, unless they are faulty or as I said the resistor or voltage is wrong, measure both with your meter.
The power supply is definitely 5 volts. I have measured it several times, and just did again. Maybe it's the source of the LEDs? I got them from a seller on eBay by the name of "Bright Components".

I seem to have blown the fuse on my multi-meter for low amp current readings, I will grab a fuse in the next day or two an update with an actual current reading.

Ahh, I originally stopped at the picture that mentioned "The RGB LEDs are a WS2812B strip".
Note: Just to mention - some types of paint could be conductive or semi-conductive (however I don't think this is the issue).
Careful there are no shorts (it appears some resistors could be shorting out).
(http://i.imgur.com/PsqJw73.jpg)


MAIN PROBLEM:
It truly appears that the resistance code is red/red/black with black (multiplier) and brown (tolerance). If so, then these are 22Ω resistors and the excessive current will cause the LEDs to fail.
The first 3 colors should be red/red/brown for 220Ω. EDIT: (I see Grumpy_Mike is a bit quicker than I)

(http://i.imgur.com/cxBF1fJ.jpg)
It is a 5 band resistor. Red + Red + Black + Black is 2-2-0 x 1 with tolerance on the end. I just measured too with my multi-meter, and they are inded 200ohm resistors. I think if you were right, they would have blown immediately, no? That would have been a lot of extra current with only 22Ohms.


For my own curious mind, would the following work. The LEDs are broken into 4 compartments regarding them sharing a positive power rail (all anodes connected), and I have a wire (4 wires total) that connect each of these sets to the positive power from the supply. Rather than changing out all the resistors, if I wanted to add lets say 50 ohms to all the leds, could I add a 50 0hm resistor to each of the wires so that way the resistance for each led would be effectively 270 ohms? I only have 1/4W resistors, so I am not sure if that would be too much load on the resistor.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 12, 2015, 11:36 pm
Quote
I only have 1/4W resistors, so I am not sure if that would be too much load on the resistor.
No that will be fine.

A thought struck me, could it be that the LEDs are getting hot inside those unventilated compartments?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Coding Badly on Jan 12, 2015, 11:49 pm

Have you replaced any of the dim LEDs?

Have you extracted any of the dim LEDs then tested them?

Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 13, 2015, 12:09 am
No that will be fine.

A thought struck me, could it be that the LEDs are getting hot inside those unventilated compartments?
How do I treat that situation with the resistors? Because I then have a parallel/series thing going on. If each light was consuming lets say 15mA after adding that resistor, and it branched off to 10 lights, wouldn't 150mA be flowing through that one 50 ohm resistor?

I suppose they could be getting warm. I didn't think they would get all that hot though to be honest. Not really sure how to test that, since the face doesn't really come off and by the time I get one out, it likely will have cooled. I guess Ill try on a breadboard, but I am sceptical.

Have you replaced any of the dim LEDs?

Have you extracted any of the dim LEDs then tested them?

I have extracted and replaced some, as mentioned earlier in the thread. Though, I didn't test them on a breadboard, I just tossed them out. After replacing the LEDs for "KLUKKAN ER", the words were back at normal brightness. The problem has now spread to "MINUTUR".
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 13, 2015, 12:21 am
I thought you wanted to add one resistor to each of the existing resistors, that is why I said it would be fine. Yes with 150mA you burn just under 2W so you need a bigger resistor.
However as I said before it looks like the LEDs, did you measure the forward voltage drop of them?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 13, 2015, 08:24 pm
I thought you wanted to add one resistor to each of the existing resistors, that is why I said it would be fine. Yes with 150mA you burn just under 2W so you need a bigger resistor.
However as I said before it looks like the LEDs, did you measure the forward voltage drop of them?
Well, I went and got a fuse today.

The I get ~9mA running through an LED in the phrase "KLUKKAN ER".

I get ~7mA running through an LED in the phrase "MINUTUR". I changed an LED and measure again, and still ~7mA.

I placed my probes on each side of an LED in both "KLUKKAN ER" and "MINUTUR". I get the same reading, ~2.9V. 2.95 in the former, 2.91 on the latter. This is the voltage drop/forward voltage right? I am not sure if the terms are synonymous, I am still trying to figure that out. Any chance you could clear up my confusion with this terminology? I get the impression forward voltage/voltage drop is the volts consumed by the component in question.

I wonder if the reason the amperage reading is different is because there is a small amount of resistance in the transistor arrays? I can't seem to account for the difference any other way.

I am starting to wonder if this is just a cause of lousy LEDs? These are the LEDs I bought:
http://www.ebay.co.uk/itm/50-x-White-LED-5mm-Diffused-1st-Class-Postage-UK-/121419713404?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c452dcb7c

Just a reminder that "KLUKKAN ER" is not connected through the transistor arrays, and is simply just connected to ground.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 13, 2015, 11:07 pm
Voltage is not consumed, that is current. The voltage across the LED is the forward voltage drop.

There is less spair voltage on the transistors because there is a permanent saturation voltage across the emitter / collector of about 0.7V, so you loose some there and so the current is less for the same resistor.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 15, 2015, 03:32 pm
Well I guess we are back to square one then. I suppose it either has to be poor LEDs, or the junction temperature is too high. If the latter, not really sure how to test that. I suppose I would need to setup something on a breadboard and enclose an LED in a similar situation. Even still, not sure quite how to measure the temperature effectively.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: ghlawrence2000 on Jan 15, 2015, 06:12 pm
If it were me, I would take everything else out of the equation and just go for Regulated 5V supply and 68R resistor per LED for say 2 or 3 LEDS and 75R resistor for another 2 or 3 LEDS and just run them constantly on a breadboard until/if you see any difference.

The Spec on the ebay advert says 3.2-3.8 forward volts 20-30mA forward current...

So :-

5 - 3.2 / 68  = 26.5mA  //  A little higher than typical but below max rating
5 - 3.2 / 75  = 24mA    //  A little higher than typical but below max rating
5 - 3.8 / 68  = 17.6mA  // Approaching typical rating
5 - 3.8 / 75  = 16ma     // Approaching typical rating

5 - 3.2 / 220 = 8.2mA   // Expected to be quite dim
5 - 3.8 / 220 = 5.5mA   // Expected to be even dimmer

This will at least drive them closer to their rated spec and prove if it is the LED's or something else....


Regards,

Graham
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 17, 2015, 06:51 pm
If it were me, I would take everything else out of the equation and just go for Regulated 5V supply and 68R resistor per LED for say 2 or 3 LEDS and 75R resistor for another 2 or 3 LEDS and just run them constantly on a breadboard until/if you see any difference.

The Spec on the ebay advert says 3.2-3.8 forward volts 20-30mA forward current...

So :-

5 - 3.2 / 68  = 26.5mA  //  A little higher than typical but below max rating
5 - 3.2 / 75  = 24mA    //  A little higher than typical but below max rating
5 - 3.8 / 68  = 17.6mA  // Approaching typical rating
5 - 3.8 / 75  = 16ma     // Approaching typical rating

5 - 3.2 / 220 = 8.2mA   // Expected to be quite dim
5 - 3.8 / 220 = 5.5mA   // Expected to be even dimmer

This will at least drive them closer to their rated spec and prove if it is the LED's or something else....


Regards,

Graham
I actually happen to have my breadboard and resistor kit out, I think I will give that a try.

Is it possible to damage an LED by driving them with too low of a current?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Zapro on Jan 17, 2015, 08:50 pm
Is it possible to damage an LED by driving them with too low of a current?
No.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 18, 2015, 06:35 pm
Is it possible to damage an LED by driving them with too low of a current?
Not only will you not damage them they will last a lot longer.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 19, 2015, 09:12 pm
I came across this:

http://lumeniquessl.com/2008/11/30/5mm-leds-generally-unsuitable-for-general-illumination/


Maybe this is a heat issue? The writer seems to hint that the 5mm bulbs I was using aren't really for continuous use. I'm guessing we are talking at about the 600 hour mark when the light brightness started to dim.

The writer also suggest using "LED packages". If I was to do another project using LEDs in such a continuous use fashion, what packages might be suitable? Are all LED packages SMD that I might possibly use in a situation like this?

Able to recommend a better dealer of LEDs?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 19, 2015, 11:12 pm
Quote
The writer seems to hint that the 5mm bulbs I was using aren't really for continuous use.
He has a axe to grind.

Quote
Are all LED packages SMD that I might possibly use in a situation like this?
There is no difference between an SMD LED and the ones he is talking about in this page.

He wants to sell you:-
Quote
Packaged LED devices, with proper thermal control,
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: arduidiot on Jan 20, 2015, 12:18 am
data log the analogRead(x) values by connecting one of the analog inputs of the data logging device to the output of the power supply board, but with a resistor that will keep the current below the max operating for the data logger, eg if you have programmed an uno with an SD card shield to log the analog input on the pin connected, see the max operating current for the uno in its spec sheet.

get a good number of samples, say leave it writing to an SD card all day. copy and paste your data into an spreadsheet and use the stats formulas to spot any surges/transient voltage spikes that have occurred. if its being rectified well enough and there is no decent spikes, well excluse the power supply and focus on the led circuit.

in this case, and If you are  not getting a few naughty little buggers at  the fringes of the bell curve of kinetic energy distribution that are damaging your circuit, im not sure exactly what your problem is, ( in my case its almost always because ive rushed the pin out and its not wired like i wrote in my book or the person who wrote the project guide has recommended, ive soldered two IC pins together that short the MCU, SOMETHING silly)

but ive attached  photo of on of the  component types i like for surge protection (range of this design, not the exact one i have attached a pic of) and they seem to be very popular
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Coding Badly on Jan 20, 2015, 03:23 am
Quote
Able to recommend a better dealer of LEDs?
Cree for white.  Lite-On for colored.

Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Jan 20, 2015, 11:57 am
data log the analogRead(x) values by connecting one of the analog inputs of the data logging device to the output of the power supply board, but with a resistor that will keep the current below the max operating for the data logger, eg if you have programmed an uno with an SD card shield to log the analog input on the pin connected, see the max operating current for the uno in its spec sheet.

get a good number of samples, say leave it writing to an SD card all day. copy and paste your data into an spreadsheet and use the stats formulas to spot any surges/transient voltage spikes that have occurred. if its being rectified well enough and there is no decent spikes, well excluse the power supply and focus on the led circuit.

in this case, and If you are  not getting a few naughty little buggers at  the fringes of the bell curve of kinetic energy distribution that are damaging your circuit, im not sure exactly what your problem is, ( in my case its almost always because ive rushed the pin out and its not wired like i wrote in my book or the person who wrote the project guide has recommended, ive soldered two IC pins together that short the MCU, SOMETHING silly)

but ive attached  photo of on of the  component types i like for surge protection (range of this design, not the exact one i have attached a pic of) and they seem to be very popular
Wouldn't I need to use some sort of potentiometer for this? If I was getting spikes beyond 5 volts, wouldn't that damage the analogue input pin? Or at the very least, would I ever get a reading above 5 volts? I think that's where its measuring range maxes out.

I also have access to an oscilloscope at a local fab lab, I could try and bring the project down there in the coming week and observe it for a while. 
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: arduidiot on Jan 20, 2015, 05:02 pm
note that i said you must connect it to the analog input with an appropriate resistor inline to drop the analog input voltage to a safe level. if you are getting spikes, it will still spike but below 5 V with that resistor. so you simply calibrate the analog read data  to reflect how large the voltage spike WOULD be if you had not have put the resistor there.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 22, 2015, 05:42 pm
at  the fringes of the bell curve of kinetic energy distribution that are damaging your circuit,
What on earth does that mean? Total rubbish to talk of kinetic energy distribution in the context of electronics.

Data logging this will tell you nothing.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: arduidiot on Jan 23, 2015, 12:09 am
electrons in the charge cloud for the current in a circuit with resistance that should limit the voltage to a certain amount but occasionally it is possible to spike over. it was kind of a joke in that it should never happen to an extent it damages the circuit if everything is wired as you've calculated.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: Grumpy_Mike on Jan 23, 2015, 12:22 am
Are you talking about Johnson noise?
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: arduidiot on Jan 23, 2015, 12:28 am
well im definately talking about noise! i dont know who  the first bloke to write about it was to be honest!

but i do know it should never appreciably happen if your wiring match your figures.
Title: Re: LEDs losig brithness at a different rate, am I damaging them somehow?
Post by: byteofthat on Feb 16, 2015, 05:09 pm
So, update!

I have had one of the LEDs I purchased powered by an arduino for the last two weeks using one of the same 220Ohm resistors.

Conclusion: Definite and noticeable dimming after just two weeks of operation. It's a well ventilated and cool area, with a good power supply. I can't blame this on anything other than the supplier.

If anyone ever comes across "bright components" on eBay, I would think twice about purchasing from them. Their products have proven to be less than "top quality".