> -----Original Message-----
> From: Harold M Hallikainen [SMTP:haroldhallikainen@JUNO.COM]
> Sent: Friday, 17 September 1999 2:20
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: 7 -segment displays
>
> On Thu, 16 Sep 1999 11:25:24 +1000 Gennette Bruce
> <bruce.gennette@TAFE.NSW.EDU.AU> writes:
>
> >>
> >        [Bruce Gennette]   I think you missed the bit about him
> >wanting to
> >multiplex the displays, at any one time only *one* of the displays
> >will be
> >operating, the other 3 isolated via the NPN transistors on their
> >common
> >cathodes being *off*. So each display will be getting 9mA for about a
> >quater
> >of the time. Cycle through the displays faster than 100 times a second
> >and
> >persistance of vision lets humans see them all continuously on.
> >
>
>         Don't think I missed it...  How bright will each segment be with
> an AVERAGE current of 2.25mA?
>
> Harold
>
        You're missing another point here - when mixing engineering with
biology you have to remember that biology has (in most cases) found the best
way to get *RELEVANT* information to the decision making area (brain).
*WHEN* the LED is getting 9mA is glows with a certain brightness that human
eyes pick up and pass on to the brain where the brain checks against how
bright it was *ABOUT* a thirtieth of a second ago; if it was about the
*SAME* then that's how the brain sees it.

        In other words biology *SEES* what in fact isn't there, but because
it *IS* there *ENOUGH* it will appear to be bright enough, even though an
engineering evaluation says it shouldn't be.

        Why don't you try it, then you'll see it works, even though you're
sure it shouldn't.

        Bye.