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View Full Version : Unequal lighting and do I use a resistors?



ZombieMacabre
01-18-2017, 08:34 PM
I'm using 5mm Green 3.5v 30ma for a string blade with a NBv3 powered by a 3.4v battery. I'm using about 120 of them currently for the blade. When the blade is lit some spots are darker than others, inconsistently through out the blade. Any tips on how to prevent this? I'm not using any resistors on the leds because I thought it was unnecessary with their forward voltage being at 3.5v. And honestly, I don't quite understand how use resistors with so many leds. Do I need to use them since there are so many wired together? Thanks for any help

jbkuma
01-19-2017, 06:10 AM
I know this can happen with cheaper LEDs and sources. It is generally recommended that you buy from a provider that can guarantee they call come from the same lot.

The math doesn't change, Ohm's Law reigns supreme. There are online calculators that can help you figure out the most efficient way to construct your array and what resistor to use. Here's one I've used http://www.hobby-hour.com/electronics/ledcalc.php

ZombieMacabre
01-19-2017, 10:35 AM
Thank you for your help. I bought these from SuperBrightLeds which I thought was good source. If anyone knows a good source that has that guarantee it would be much appreciated. Otherwrwise thanks for your time!

Gallandro
01-19-2017, 04:17 PM
When the blade is lit some spots are darker than others, inconsistently through out the blade. Any tips on how to prevent this?

Yes. Assuming that all your soldered connections are consistently good, the difference in brightness is due to the individual LEDs. What we're talking about is called 'binning', which means sorting LEDs by brightness and color. If you search around, some places claim to do it for all their LEDs, but check out Wayne Schmidt's page: http://www.waynesthisandthat.com/lightsaber.html
Wayne is a very interesting dude. He does things that most people would never take the time to do, and it is very educational if you're interested in string blades. Near the top of the page he has set up a pretty simple test rack that will light up a bunch of LEDs at once, allowing him to compare and sort.

Renaissance Jedi
01-19-2017, 05:50 PM
Check out Slothfurnace's builds. He's mostly done string blades, and he has some pretty in depth descriptions and photos of what he's doing.

ZombieMacabre
01-19-2017, 10:38 PM
I will definitely check those out. Thank you guys so much!