DVDdoug:
And if you wire them in parallel without current limiting resistors, there is nothing to assure that the current is divided equally between them.
Alright thanks, that seems like it might be an issue. I have a whole couple of 7219s at my disposal so I think I might as well go with two drivers. That means more complicated code, but really it shouldn't be that bad.
Page 10 of the data sheet:
Selecting RSET Resistor and
Using External Drivers
The current per segment is approximately 100 times
the current in ISET. To select RSET, see Table 11.....
I was a bit confused by RSET at first, I'm not sure how I missed it. Also the graph on page 4 seems to answer my other question about getting segments down to 10 or 20mA.
So now if all the segments are being properly connected to the drivers (instead of being wired in parallel like I proposed), and I have the appropriate RSET resister between ISET and V+, I should be fine without any more current-limiting resistors, right?