Okay, let’s figure out the resistor. First we need the battery voltage. I’m going to assume you’ll be using NiMH rechargeables, both because you’ll be playing with this a lot and because they’re better for the environment. They’re nominally 1.2V per cell, although for this application they should still be quite usable when they’ve drained to 1.0V per cell. So you have a supply voltage range of 4.0 – 4.8V.

I don’t know how much electronics you know and how much you want to know, but the supply voltage is going to be split between your LED(s) and your resistor. Your LED specs say the LED will take 2.1V, so the remaining 1.9 to 2.7V (depending on battery charge) will fall across the resistor.

Now we want to calculate a resistor value that gives 25mA at 1.9 to 2.7V. Given that I (current) = V (voltage) / R (resistance), you can rewrite to get R = V/I. So

R = 1.9V / .025A = 76Ω
R = 2.7V / .025A = 108Ω

So a 108Ω resistor would be perfect when the NiMH cells are fully charged and a 76Ω resistor would be perfect when they’re a bit discharged. If you want to run the LEDs at the full 25mA, I’d compromise and use a widely-available 100Ω resistor.

That said, I’m guessing you won’t want the full 25mA / 6.3mcd. I think you’ll get lens flare on your videocamera at that brightness, and in my experience I think you’ll actually want something closer to 10mA. Assuming you can make sense of the equations above, I’ll leave those calculations as an exercise for the reader. Plus you can always get some different sized resistors in the 100 – 1000Ω range and just try them.

I will follow your advice and use the parallel design with one external resistor. However, I’m not sure how to calculate the amount of resistance i need for the circuit to work as intended.

Thank You.

What color LEDs are you using? Different colors have different voltage drops, and I can show you how to calculate the resistor you’ll want to use. For this application, if you’re using all the same color LEDs, I’d suggest one resistor and all the LEDs in parallel behind it. If different colors, probably a separate resistor for each.

The resistors will take care of the overheating problem, too.

Would i need to calculate the amount of voltage i need, or should i find a battery holder like yours? (I need 6 LED lights on the glove, – one on the palm) Are resistors necessary?

What would be the best design for that many LEDs, series? parallel? a combination perhaps?

I have noticed that the lights get hot quickly, do i need to worry about that or would the glove be enough protection?

Thank you very much for you time Keith.

P.S The link to Leah Buechley was very useful.

It was wire made for winding magnetic coils of some sort, for transformers or instrument pickups. If you like to salvage things, you could find a small transformer from inside a dead CRT monitor; or you might be able to use the 30-gauge wire from Radio Shack’s magnet wire assortment.

Also definitely check out the work of Leah Buechley, a pioneer in making wearable circuits. I know she has information somewhere on her site on the conductive thread she uses.

You know, I thought to myself the second I put the glove on, “boy! this is the most comfortable, well-fitting LED glove I’ve ever had the pleasure of wearing!” Thank you for your consummate sartorial professionalism.