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LED questions-- how many on a given battery and resistors with conductive thread? Answered

How do you figure how many LEDs you can use with a given battery, . and why don't you need a resistor when weaving an LED into fabric.. or do you. Is there a diff between using conductive thread and wire in that regard....?

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steveastrouk
steveastrouk

11 years ago

What typical voltage and how many LEDs do you want to use ? On 5V a typical red LED needs aroun 150 Ohms of series resistance, that's 100" of your thread.

Altenatively, use ACTIVE control of the LEDs, by using a circuit like the one here. This automatically compensates for the wires for you.

LED driver.PNG
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ingamarie
ingamarie

Answer 11 years ago

nice site, thanks!

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steveastrouk
steveastrouk

11 years ago

Since the thread is a rather worse conductor than normal wire, its going to depend very much on the thread. I've seen some circuits where the thread itself can work as a resistor as you suggest, but I'm not sure its a good idea. the threads terminations, which are often wrapped around the edges of a circuit board, are susceptible to aging, and what was a pretty reasonable current limiting resistance when you made it, gets more resistive with time - so your LEDS get dimmer with time.

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ingamarie
ingamarie

Answer 11 years ago

hmmm. As it turns out I have about 1-1/2 ohms of resistance per inch of thread, so the problem seems to be not enough current rather than too much. And you say that is going to get worse with time.  hmmmmm.