Pretty easy to put one smallish resistor (to limit source I=25mA for pin
port safety) in series with each Column Select pin, drive each of those
Column Select pins from a PIC pin (or other sneakier method), and then
pull each of the 7 segments high in turn to light the LED.  That's only
2 resistors.

The 1-pin Shift Register trick could be used here to control the column
select outputs, if desired.  Just only turn one Column Select pin on at
a time, as both at once would be hard on the sourcing pins.

Or, use a couple driving transistors/FETs and invert the drive off the
one pin so only one of the 2 Col. Sel. pins CAN be grounded at a time.
3-transistor solution, that way.

  Mark

Ismael M. Khangane wrote:
>
> Hi to all:
> First of all, happy new millenium  to all.
> I am making my own Pic-Trainning Board whereby I can do practicing
> most/all peripherals it gets ( PIC17C756 & PIC16C76 ). I have tested the
> 7-seg display with 470 ohms to @ pin and I realized that they are have a
> cathode comun. But now I would like not use those resistors as they are
> many  for ( Two 7-seg displays ).  Am I going to ruin them as voltage
> output,Voh and current output Ioh  are 5.5V and 25mA respectively? they
> are FND 507 from Korea. Anyone who has already experienced this p'se
> give me an advice for time saving.
> Regards,
> Ismael.
> Madrid, Spain.

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