Bad LED?

[thejoe]

Only my second build... MXR distortion + works fine sounds great. Can't get the LED to light up. Its a green LED. startd with an 8k7 resistor as per the schematic. switched to a 1k afterwards. neither one worked. suggestions?

Joe

[gez]

Are you sure it's the right way round?

[thejoe]

about 90 percent sure. I'll try and switch it and let you know how it goes.

[The French connection]

about 90 percent sure. I'll try and switch it and let you know how it goes.

Hi! That leaves 10 % off...Have you touch the led with your battery or 9V power without a resistor? I'm not kidding you, i've made this mistake once...and flash, Led's dead...
Now i know...
Try another one...

Dan

[thejoe]

Never thought of that. I'll try another one. I did reverse the LED and still nothing. Is it worth mentioning that it's a 1k resistor. As I said, the schematic was for a red LED and a 4k7 resistor. I had read that with a green LED different value is needed so I went to a 1k. Make sense or make problem?

[The French connection]

more series resistance = dimmer
less series resistance = brighter

You need some resistance otherwise you can damage (fry) the LED.  If you bought the LED(s) from a supplier, they usually quote figures in their catalogues (online/whatever) for max forward current.  You then need to use Ohm's law to calculate the minimum value resistor you can get away with in order not to exceed this figure and fry the LED. 

R=V/I

Where I is the max current the LED can take.

It's always advisable to make this current limiting resistor slightly bigger - it's never a good idea to run things close to the max.

If you got away with connecting your LED directly to your supply without a resistor and without frying it, congratulations.  Don't bank on that happening everytime though...

That will help you...next time...

http://www.muzique.com/schem/led.htm

or

http://ledcalc.com/

Or search google for Led calculator and else...

[Radamus]

Have you touch the led with your battery or 9V power without a resistor? I'm not kidding you, i've made this mistake once...and flash, Led's dead...
Now i know...
Try another one...

I did that with a couple home made optoisolators. Red LED's take a beating. Green fry a lot easier in my experience. But that's only been a couple of LED's so far. Your LED is probably just cooked.

[thejoe]

I tried a new LED with a 390 ohm Resistor which seemed to be what the calculator said to use but still nothing. I'm gonna keep trying. There is a chance that the resistor was fried.

[gez]

Sounds as though something isn't connected properly (no current flowing) or a joint is dodgy.

PS  If this were me, I'd stick with a larger value resistor until you find out where the problem lies.

PPS, test your LED out-of-circuit (breadboard etc) to rule out the possibility of it being fried.

[ayayay!]

Grab yourself a cheap motherboard battery (like a Panasonic 3.2 Volt) and test your LEDs.  I'll be they're fine.

Do what Gez said.  Get your meter out and make sure you actually have current flowing to the LED on your pedal.   

[thejoe]

Got it!! 390 resistor was fine for the LED. Turns out I had the LED wired backwards and to the wrong slug on the 9v.
Thanks to everyone for the help.