> That's not so easy if you decide to put the transistors in
> there (which are
> needed if you want more than 25mA total per digit).

Or more than 25 mA peak on a segment, which for 8 digits amounts to the
same as the common current.

> but relies on the fact that PIC pins can have 3 output states.

of course

> It could be
> done, but would require more external parts than just a
> BJT and a base resistor.

I used this in a 4 digit display. For the digit common current I used a
PNP as emitter follower. This relied on the transistor being off when
the base is floating, which might not always work, but could be cured by
an extra resistor. For the segment current (which gets higher with an
increasing number of digits) an NPN follower might be used, but I am not
sure this would work.

I consider this approach mainly for fun, as it requires both weird
wiring (you can not connect all 'a' segments together) and funny
programming (the segment mapping is different for each digit, and spread
over 9 bits). It was more usefull in the old days when the 16c84 was the
only readily available 'flash' PIC.

Wouter van Ooijen

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