[sdiy] LED's on negative rail??

[Paul Maddox]

Hi,

> I'm working on a few things that run almost entirely off the postive rail.
> Since LED's draw a significant amount of current (the light has to come
> from somewhere), I'm thinking that I should run the LED's off the negative
> rail to balance things out.  However, I've never seen that done.  Is there
> any reason why??  Is it a noise issue??  As far as I can tell, the LED's
> would "see" the same difference.

Hmmm, nice idea...
I guess you mean getting whatever it is to switch to ground?
so you have

-V ----|<---- siganl

The problem is you need to make sure that the signal NEVER goes positive, it
must be either 0v or open circuit.. easy to do with a CPU, not so easy with
TTl/CMOS/Opamp.

Paul