Re: Matching brightness across multiple 7-seg LED displays
From: Steve (me_at_privacy.net)
Date: 10/10/04
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Date: Sun, 10 Oct 2004 08:23:47 GMT
"Jonathan Kirwan" <jkirwan@easystreet.com> wrote in message
news:3hkbm01jo143b13c755da2fpsfpqv9gonh@4ax.com...
> On Thu, 07 Oct 2004 22:40:32 GMT, roma <john-p@shaw.ca> wrote:
>
> >I've this problem before and instead of findind what is a fault I simply
> >insert a 1K trimpot set at minimum resistance in series with the driving
> >transistors then tune all the displays to match the lowest brightness one
.
>
> Yes. Or, if one is able to consider the idea, PWM all the displays (they
are
> being used three at a time in Steve's system, so I'm guessing they are
already
> in a 1/3rd mux situation) and calibrate an adjustment factor for two of
the
> digits. Something like: assume each digit at 100% of their respective
time
> slots, select the dimmest (as you suggest), and then tweak down the mux
time of
> the other two, leaving slight time gaps where no digit is driven at all.
>
> Jon
Hi Jon. Thanks for the idea. The software cal method would be good in that
it won't add any more components. Only problem in my case is that I've
totally run out of codespace, having already crammed in more than I
bargained for. If I found a few bytes of ROM spare I could just about
hard-code the cal factors, but that would mean each PIC would have different
code, which is not great news. To do it a better way, such as holding the
factors in internal EEPROM, would add more code that I really can't squeeze
in as it stands. My fault for not allowing enough slack in the PIC!
Steve
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