Pedal works, LED doesn't

[ferrinbonn]

Hi guys. Just finished my 2nd build! I did a 2nd Moar Overdrive, this time using correctly sized components and managing to fit it in the 1590G box as intended. It sounds better than the first one too. I don't know if the components are the difference, or the fact that the soldering and wiring are much cleaner, but I'm very happy with it.

The only problem is the that LED isn't working. I wired it straight to the LED spots on the board, just like I did with the first build and it didn't work. One big difference with this second build through is that I used a 3PDT breakout board (http://www.rullywow.com/product/3pdtv3-1a/) and since that board has its own LED spots, I thought maybe that was the problem.

So after adding the resistor to the breakout board, I took a second LED and touched it to the pads on the breakout board and it lit up just fine. So from there, I attached wires to the breakout board and then to the LED after cutting the leads short so that I could put the LED back in the original hole, and again, the LED won't work. And yes, I confirmed that I used the longer lead on the positive pad.

So what gives? I think it's unlikely that I got two defective LEDs, and also unlikely that there was some problem with the pads on both the main board and the breakout board. Are LEDs easily damaged by heat? The only thing I can think of is that I somehow damaged them during soldering, although I really doubt it. I can't think of anything else that would be the problem, and the pedal continues to work and sound great.

Thanks for any suggestions. It's not the end of the world if I have to live without the LED, but after putting in the work to build a 2nd one of these, I really want it to be perfect.

[icecycle66]

Does the LED work when the circuit is out of the box?
If so, then one of the LED leads is probably grounding on something while it's in the box.

[m-Kresol]

Does the LED work when the circuit is out of the box?
If so, then one of the LED leads is probably grounding on something while it's in the box.

If you got the LED from tayda and it's a 3mm one, this is very likely. My last batch of 3mm leds all had the legs not completely covered by the LED plastic housing, thus grounding the + side on the enclosure and not lighting up. I fixed it by covering the spots with a few coats of nail varnish. Or you could use a bezel

[ferrinbonn]

5 mm green LEDs from Radio Shack. I forgot to order when I did the big parts order online.

I haven't taken the whole board out, but I'm not sure why that would make a difference. The strangest thing is that the LED worked when just touching it to the pads on the 3PDT breakout board, but when I connected that same LED with wires from those same pads, it no longer worked.

[devilsnight]

post a picture. maybe we'll see something that your not?

[midwayfair]

Measure the voltage on the anode of the LED.

Voltages, people! Stop guessing!

[ferrinbonn]

I've never done any voltage measurements and I'm not sure how. Do I use the multimeter between the anode and the ground or the positive?

I used a 6.8k CLR on the breakout board, so what voltage should I be getting for the LED with that?

[midwayfair]

I've never done any voltage measurements and I'm not sure how. Do I use the multimeter between the anode and the ground or the positive?

I used a 6.8k CLR on the breakout board, so what voltage should I be getting for the LED with that?

https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/measuring-voltage

Forgot to answer your second question. The forward voltage of the LED will always be the voltage you see when measuring from anode to cathode, whether there's a power supply involved or not. (I am specifying this way because the CLR could be between the anode and the power supply or the cathode and ground, even though it's usually the latter.) The current limiting resistor must be any value that produces a current less than the maximum current described in the data sheet for the LED. If you aren't sure how to calculate the available current, Google current limiting for LEDs or a similar phrase. It's a very simple bit of circuitry that gives you an opportunity to learn about forward voltage for diodes, Ohm's law, etc.

The reason to measure the voltage is that if it's anything EXCEPT the forward voltage of the LED, you know something's gone wrong with the LED. Regardless of whether you think it's unlikely you got two bad LEDs, you can't tell with your eyes if there's voltage on the anode.

[jimilee]

Measure at the pads where you soldered them. Also, if you touch the anode and cathode on the meter to the anode and cathode to the led, it should light up. Are you sure it's a 6.8k and not 68k or 6.8r?


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