Ok so here is the deal.
I need to wire 8 white LEDs together in Parallel, so the current going to each one is equal.
I have 8 identical LEDs that each require 3.0V at 20 mA.
I have a power supply to two rechargeable AAA batteries at 1.5V each, totaling 3.0V.
My question is how do I ensure that each LED is getting its 3.0V at 20 mA? Do I need to have a resistor somewhere on it?
Also, how do you attach LEDs to a wire? Do I need to solder them on?
Okay, so, 8 LEDs at 20mA each is only 160mA, so you're well within the capabilities of the batteries.
In theory, you're close enough to the forward voltage of the battery that you can get away with leaving out the current-limiting resistor, but it's ugly, you might not be able to light the LEDs at all, or you might blow them.
The [url=http://ledcalc.com/#calc]Metku LED calculator[/url] and some fiddling about on my part makes me want to recommend bumping up the power supply to three, or maybe even four batteries, giving you either 4.5 or 6 volts, which will give you the power to light the LEDs for sure.
With the LEDs in parallel, and one current limiting resistor, you'd need a 1/2 Watt 10 Ohm resistor for 3 batteries, or a 1 Watt 22 Ohm resistor for 4 batteries.
Another option, if you don't want to use such beefy resistors, is to use a separate resistor for each LED, which would mean a few 1/8th watt resistors in 82 Ohms for three batteries, or 180 ohms for four batteries.
[QUOTE=Lapsus;31147663]Okay, so, 8 LEDs at 20mA each is only 160mA, so you're well within the capabilities of the batteries.
In theory, you're close enough to the forward voltage of the battery that you can get away with leaving out the current-limiting resistor, but it's ugly, you might not be able to light the LEDs at all, or you might blow them.
The [url=http://ledcalc.com/#calc]Metku LED calculator[/url] and some fiddling about on my part makes me want to recommend bumping up the power supply to three, or maybe even four batteries, giving you either 4.5 or 6 volts, which will give you the power to light the LEDs for sure.
With the LEDs in parallel, and one current limiting resistor, you'd need a 1/2 Watt 10 Ohm resistor for 3 batteries, or a 1 Watt 22 Ohm resistor for 4 batteries.
Another option, if you don't want to use such beefy resistors, is to use a separate resistor for each LED, which would mean a few 1/8th watt resistors in 82 Ohms for three batteries, or 180 ohms for four batteries.[/QUOTE]
I have a maximum of three batteries (I lost one rechargeable :D)
So would this work as a resistor? [url]http://amzn.to/oQmxIi[/url]
And where would I attach it?
The resistor would work, but it'd be a little silly to spend $5 shipping on a $0.98 part.
It'd go in series with the batteries, though I'd also recommend a power switch.
Here's a little diagram, I'm sure you can guess where the other 6 LEDs would go, and how to stick the third battery in series. Fritzing is a bit limited.
[img]http://i.imgur.com/HRfnw.jpg[/img]
Is this for the cane in the picture from one of your older threads?
[img]http://www.wired.com/underwire/wp-content/gallery/tron-concept-art/tron-legacy_michael-sheen-as-castor-660.jpg[/img]
[QUOTE=Lapsus;31147909]The resistor would work, but it'd be a little silly to spend $5 shipping on a $0.98 part.
It'd go in series with the batteries, though I'd also recommend a power switch.
Here's a little diagram, I'm sure you can guess where the other 6 LEDs would go, and how to stick the third battery in series. Fritzing is a bit limited.
[img]http://i.imgur.com/HRfnw.jpg[/img]
Is this for the cane in the picture from one of your older threads?
[img]http://www.wired.com/underwire/wp-content/gallery/tron-concept-art/tron-legacy_michael-sheen-as-castor-660.jpg[/img][/QUOTE]
Yes that is the picture.
Um I have that battery thing, and a switch.
And I'm also getting the PVC and the LEDs on Amazon, so don't worry about the shipping.
How do you actually go about attaching the LEDs to the wire though? Do I strip the wire and wrap it around the LEDs? Is there some other way?
Personally I'd solder them to the wire.
[QUOTE=HatredViral;31155177]Personally I'd solder them to the wire.[/QUOTE]
Alright thanks for your help everybody.
Need to go pick up the solder and order all the materials.
Expect a tutorial up when I get back home from the summer :P
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