Understanding LED

E

EGRENIER

Well-known member
I’ve been working on a dual pedal and wanted to use a bi-color led to indicate which way the effect was running; A-B vs B-A..

My though was simple, and was to reproduce the standard power LED circuit through the foot switch. So started testing with a 9V supply and a 4K7 resistance. I noticed the green side of the led was really faded…. So I wonder if I could supply more current to the LED to get it brighter.

After calculation I ended up with a current value of 2mA with a 4K7 (4700 / 9 = 0.0019). The led spec are for 20mA, so my question is:

Why do we use such a high resistance in our circuit ?

If I were to use an 800R it would give me about 11mA… well within tolerance of the led….

So why ?
 
I probably can’t really answer your question to a technical degree you are looking for. But 4k7 is just a starting point. different LEDs will require different resistance to achieve a desired brightness and that desired brightness is subjective. In a lot of cases I personally will run a 10k because I don’t like really bright LEDs because I usually play in dim lighting
 
Paradox916 said:
I probably can’t really answer your question to a technical degree you are looking for. But 4k7 is just a starting point. different LEDs will require different resistance to achieve a desired brightness and that desired brightness is subjective. In a lot of cases I personally will run a 10k because I don’t like really bright LEDs because I usually play in dim lighting
Click to expand...

You are actually answering my question. I’m not technical, just did research to figure out what value I could use. Your answer is very much valid, the only reason I could imagine is that brightness is relative to ambiant light and people may not like bright led in darker situation.

What really got me wondering is the green led is so much darker (less bright) than the red… So I think I’ll drop the resistance on the green side trying to balance them out.

What I worry about is if higher current would reduce the life span of the led….
 
You should probably experiment on a breadboard to see which resistances you’d prefer. You may be overthinking it, but what do I know.

If you do a google search about lighting up a diode on a breadboard, nearly all of them have a CLR of 100 ohms or higher. This is purely to protect the diode from burning out. The higher the resistance the dimmer the LED becomes. If you’ve got a superbright one you may get up to 20-40k to control the brightness. Since there’s such a wide range of resistors to use I suggest like I did above to whip out a breadboard or some vero with sockets and experiment.
 
BuddytheReow said:
You should probably experiment on a breadboard to see which resistances you’d prefer. You may be overthinking it, but what do I know.

If you do a google search about lighting up a diode on a breadboard, nearly all of them have a CLR of 100 ohms or higher. This is purely to protect the diode from burning out. The higher the resistance the dimmer the LED becomes. If you’ve got a superbright one you may get up to 20-40k to control the brightness. Since there’s such a wide range of resistors to use I suggest like I did above to whip out a breadboard or some vero with sockets and experiment.
Click to expand...
I did, even tho I don’t have a breadboard. Made it work with alligator clips and test 3 values: 4k7, 2k6 and 800R. Even went as far as measuring the emitted lux. From 4k7 to 800R, we are talking at least 4 time the lux value.

This build is for a friend, he gigs, and if led brightness can be a pain on stage, maybe I should instead lower the red brightness to match… Really looking for opinions…
 
Only thing I've ever done is adjust to taste - I always socket my LED resistors to be able to adjust.
Seems like a lot of electronics manufactures dont bother and just try to go by specs - and wind up with LEDs that have the brigntness of a laser and could be seen from the moon. Yeah, MXR Dyancomp blue led I'm talking about you ! :)
 
Glad you got it sorted out, thread was a good read — though I confess I’ll need to read it again to learn from it.


I found that while red LEDs are very good listeners, the green ones are the most understanding (though to be fair I try to talk to the amber ones also, and even the blue ones once in a while).

I use a dab of opaque or diffused nail polish to take the edge off overly bright LEDs on commercial pedals, or if I’m too lazy to change out a CLR.
 
It's pushing it. If you need that much current, then maybe you need a different LED. My experience with bi-color LEDs is most of them are weak. I picked up some tri-color LEDs from EG and they are pretty bright. Just pick the two colors you like and cut the other lead off. Or power red & green to get yellow.
 
Well considering the life span of a LED, I’m pretty sure my pedal will fail before the LED.

However, about that bi-color LED, I pulled the ground from the grd pad normally use by the output jack. Is ground a ground and it dosent matter or using a a signal ground for power an issue ? I do have some sort of grounding issue on the pedal that I have yet to troubleshoot.
 
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