LEDs losig brithness at a different rate, am I damaging them somehow?

[byteofthat]

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

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?

[ChilliTronix]

Well, you have one resistor per LED so I can't think of a good reason for there being a problem...

[byteofthat]

Could a voltage spike situation when being plugged in be the problem? Would it damage the LEDs in such a fashion?

[ChilliTronix]

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?

[byteofthat]

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?

[ChilliTronix]

It does, but the only issue I can think of then is a dry joint in the circuit for that word.

[byteofthat]

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!

[ChilliTronix]

Re melt the joints just in case. I can't think of another explanation at the moment.

[byteofthat]

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.

[DVDdoug]

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.)

[Grumpy_Mike]

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.

[cjdelphi]

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...

[TomGeorge]

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.......

[Chagrin]

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.

[dlloyd]

Regarding the RGB LED strip (WS2812B) in the clock, this link is a good reference - look at the warning section 1/2 way down the page.