Diffused Green Led Resistor?

[nascarbean_97]

So I've found all kinds of opinions on what the right resistor is for the regular old red leds, and the clear blue ones, but does anybody have a preference for diffused green?

I used a 2k2 and it's pretty dim, anybody have a preference?

[R O Tiree]

It's not a matter of preference per se but maths...

Put your 9V battery across the 2k2 and the LED in series. Measure the voltage across the LED. Let's say it's 1.9V (which is what I just measured on the green LEDs in my drawer). Next, find out the max If (forward current) that it can take. You'll find that on the spec sheet on the website you bought it from. If you can't find it, then go with 10mA - that should be bright enough.

OK, time for the maths... 9-1.9 = 7.1V dropped across the resistor. You want to run 10mA through it, so Ohm's Law says R=V/I=7.1/0.01 = 710 ohms. (Out of interest, you're running just 3mA through it at the moment, so no wonder it's dim.)

Nearest common value, then is 820 (drops the current a little, to be on the safe side). 680 ohms would raise the current a little, but not unduly, as most will cope with 20mA maximum.

This raises the question of whether you want to run it at maxi chat? The answer is probably not. My advice is to go with half the max If. I use a 1k in all my pedals and the LEDs are always plenty bright enough

[PRR]

> a preference for diffused green?

While color and spread make a difference, "similar" LEDs at the same current (voltage and resistor) may give quite different visual impact. Also some folks play outdoors at noon, others play vampire bars.

So try and see.

> I used a 2k2 and it's pretty dim

If it is "half as bright as you like", try "half" the resistor.

It isn't fussy. 50% either way will be fine. Whatever is handy.

So if 2K2 is not enough, half is 1K1. 1K is probably handy.

"Too much" for 9V supply and most LEDs is anything less than 350 ohms. (9V, minus roughly 2V-3V for LED, leaves 6V-7V across resistor. 7V across 350 ohms is 20mA, a typical maximum for a basic LED.)

This ignores battery drain. If you have a simple 1 transistor booster eating 1mA, the battery lasts a long time. If you go as low as 350 ohms, 20mA in the LED, battery life is 21 times shorter! 95% of battery energy goes to the light, not the sound. At 1K, ~~7mA, that's still a drain. OTOH a larger effect circuit might draw 30mA, a 2K2 LED resistor only 3mA, so the LED power is a small part of the total battery drain. And any wall-power supply can feed many bright LEDs without strain, then you can be generous.

[nascarbean_97]

I often only build effects with a power supply jack, so I think I'm fine.
I'll try the 1k that you suggested, thanks.