[Noisebridge-discuss] A simpler circuit for ... [driving multiple LEDs with minimal batteries]

[Christoph Maier]

On Sun, 2011-01-16 at 10:08 -0800, T wrote:
> 
> 
> Here's another idea in the thought of not getting overwhelmed by
> building complex circuits.
> 
> You can get a device called a "Constant current diode (also called
> CLD, current limiting diode, constant-current diode, diode-connected
> transistor or CRD,current-regulating diode)"
> 
>  https://secure.wikimedia.org/wikipedia/en/wiki/Constant_current_diode
> 
> As long as your battery has a higher voltage than your string of
> diodes (add up the voltage drops if you run them in series as others
> have advised) and is capable of producing the current (milliamps),
> picking a constant current diode that has a current rating at or below
> the rating of your LEDs should do the job in a very simple circuit:
> 
>  --- - battery + ---- CLD |> ----- LED ---- LED ---- LED .... ---
> |                                                                |
>  ----------------------------------------------------------------
> 
> 
> So something like a 12V camera battery should be able to drive up to 3
> white 3V LEDs or a few more of the lower-voltage colored variety, a 9V
> "transistor battery" should be able to drive 2.
> 
> 
> And it lends itself to experiment too... you can hood up the battery
> and the CLD and one LED, and it should work fine (since it's
> current-limited it will limit voltage too), and you can hook up two,
> and you can hook up three, and if you hook up too many they just won't
> light up, no harm done.

Norton equivalents of waffle irons come in particularly handy if you're
running a fever, feel cold, and need an efficient heater. 

Not quite as efficient as a flaming sousaphone, though.
http://www.youtube.com/watch?v=wMhLm2BVjEU