Been trying hard to squeeze my PIC boost gauge (from some months
ago) into a round gauge enclosure, and that means elimination of
as many external parts as possible.  So I'm looking at every
component and thinking of why I really need it.  Converted the
circuit from 10 direct-driven LED's to 12 MUX'ed LED's (3x4 config)
and then this occurred to me last night...

http://www.avn-tech.com/stuff/mux_no_transistors.jpg

Not shown in the pic is that all LED cathodes are to the left.
Also, the dashed line represents the division between the main
board and the display board (yes, I need 2 round PCB's).

I could possibly eliminate the driver transistors since I have
extra ports to generate enough current.  The reason of tying the
lines together is that I can reduce the number of wires going
between the main board and the display board.

I think I'm not violating any PIC rules here:
- I can keep the tied-together lines at the same logic-level by
        keeping them on the same port.
- By multiplexing, only one set of 4 is on at any point in time,
      so I'm within the port's total max current.
- Also within the chip's max current.

BTW, I need the 16F872 since I need an A/D.  Nothing smaller w/flash.

I guess what I'm looking for is the experts' blessing on this.  Is
there something wrong here that I am missing?  Or shall I start
my PCB layout....?

Thanks,
-Neil.

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