[Noisebridge-discuss] driving multiple LEDs with minimal batteries

jim jim at systemateka.com
Wed Jan 5 20:18:24 UTC 2011

   i'm curious as to the power aspect: 

   assuming an AA battery and a black box gizmo that 
converts input voltage to 30 VDC out, connecting one 
LED requires a current limiting resistor. connecting 
two LEDS requires a smaller current limiting resistor. 
more LEDs, smaller current limiting resistor.... 
   having not done it, i don't know that some number 
of LEDs requires no current limiting resistor, is 
that the case? if so, then i'm guessing the internal 
series resistance of the power supply (the black box 
gizmo and/or the battery) provides the limit, yes? 
   regardless, it seems that each LED represents 
power consumption of current times voltage drop 
across the device. a few LEDs presents no problem, 
but above a certain number, it seems there may be 
some kind of failure, possibly dimmer LEDs or hotter 
battery or blackbox gizmo weirdness or.... 

   what's the truth about this? 

with thanks 

On Wed, 2011-01-05 at 12:02 -0800, Michael Shiloh wrote:
> It's Rolf, copied on this.
> On 01/05/2011 11:49 AM, Jake wrote:
> > There was a guy who came to Circuit Hacking Mondays who made these tiny
> > circuitboards with a Linear Technologies chip that boosted power from a
> > low voltage to up to 30 volts with a set current limit.  He brought them
> > to CHM as a kit i think, and was making umbrellas with hanging lights.
> >
> > Mitch or Miloh will know who i'm speaking of.  He was really tall and thin
> > and older than Miloh...
> >
> > anyway the great awesomeness of his kit is like this:  you hook up a
> > battery to it (a single AA, rechargable or not) or a lithium-whatever, it
> > doesn't care - and it will work.
> >
> > On the output side, you simply wire all your LEDs in series - one after
> > another, any colors, no resistors necessary - and the thing will power
> > them all with the same current.  Regardless of the state of the battery
> > (until it is empty)  Up to 30v or 10-15 LEDs in series per board.
> >
> > I think the appropriate way to power a scarf is with a single AA sized
> > battery.  People can use a disposable battery but a rechargable AA is
> > ubiquitous and appropriate, and an be charged separately from the scarf.
> > And a scarf is something that will hopefully outlast any LiFePo battery or
> > NiMH cell, so it has to be a standard, replaceable cell like a AA.
> >
> > -jake
> >
> > ---- original mess ----
> >
> > I'd like to do a soft circuit scarf or three, but I'm always running up
> > against the problem of power. I usually use fairly low power LEDs
> > (<2v) driven by a 9v battery or one of sparkfun's LiPos.
> > I've heard tell of somehow being able to power more, but I'm still
> > learning
> > this EE stuff. Could some kind person point me in the right direction?
> > Meredith
> >
> > _______________________________________________
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> > Noisebridge-discuss at lists.noisebridge.net
> > https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss
> >

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