At 12:18 AM 3/14/2004 +0000, you wrote:
> > > The answer is either to use a lower average current (perhaps
> > > upgrading the display to something that give more mcd/ma) or
> > > add some drivers. In the case of the CC displays, you could add
> > > an octal source driver to drive the segments. Source drivers
> > > are generally more expensive and drop more voltage than sink
> > > drivers, however.
> >
> > I've never come across these drivers before (like I said, I'm
> > fairly new to electronics really) so I'll look into them. I just
> > did a quick google but didn't find much - if anyone has any links
> > to simple example circuits using them I would be grateful.
>
>Actually, I was just wondering, could I just use another tranistor
>when selecting the porta pin so that power would then be taken from
>the main positive power rail? (I might be way off here...)

Yes. You can use an emitter follower, but that's one transistor
per pin, and there should be a series base resistor to prevent
possible oscillation. Eg. (only one LED shown, but you get the idea)


               Vdd
               |
pic         |/
--[300R]----|    2N4401 etc.
             |\ E
high=on       |
               |
             [Rs]
               |
               |
              ---
              \ /  LED
              ---
               |
            |/
pic--------|     NPN
            |\ E
              |
             Gnd


Or use a PNP transistor, which is even a bit better:


               Vdd
               |
pic         |/ E
--[1K]------|    2N4403 etc.
             |\
low=on        |
               |
             [Rs]
               |
               |
              ---
              \ /   LED
              ---
               |
               |
            |/
pic--------|    NPN
            |\ E
              |
             Gnd




















>Matt
>
>--
>Matt N. Marsh
>Email: matt@mattmarsh.net          Yahoo: marshmn
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>                                      AIM: MattMarshUK
>
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