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Message from discussion High power IR LED control w/arduino and IR camera
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Nick Vermeer  
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 More options Aug 24 2012, 11:03 am
From: Nick Vermeer <nicholas.verm...@gmail.com>
Date: Fri, 24 Aug 2012 11:03:22 -0400
Local: Fri, Aug 24 2012 11:03 am
Subject: Re: [NYCR:Microcontrollers] Re: High power IR LED control w/arduino and IR camera
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Hi Sameer,

I worked with you a bit on this yesterday.  Can you send a schematic of how
you have the LM317 hooked up?

Raph thought you had the LM317 hooked up as a constant current source, but
I want to verify that circuit is correct.  If it is constant voltage, then
each LED is adding it's voltage drop to the chain, which will cause a drop
in current when the power supply is constant voltage.

On Fri, Aug 24, 2012 at 9:46 AM, Sameer <par...@gmail.com> wrote:
> Hi everyone-- question about the LM317 --

> I've been using the LM317 to power the LEDs just fine, when last night at
> Resistor it was suggested that I actually measure how much current I was
> putting through the LEDs. I did that and it turns out that when I have all
> 7 LEDs in series I'm only running about 180 mA through each LED. Now the
> consensus was that this is probably fine because with all the LEDs running
> at full current it could actually cause vision damage (and because it's IR
> you won't have a reflex to close your eyes).

> However, I am curious why this is, does anyone have ideas?

> When I run the circuit with no load, I get 704 mA. With just one LED I get
> just about 698 mA. I don't think it is because the battery has any internal
> resistance/current limiting. I'm using a 2200 mAh 30C LiPo, which means it
> can spit out 66A right? So that should be more than enough I would think.

> Thanks,
> -s

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