Sourcing vs. Sinking

I have a problem I need a little help with. esentialy I am desiging a fuel consumption computer (automotive). The specs have 3 bargraphs, Fuel Level, MPG, and range. Each graph consists of 2 12 segment arrays, which as my luck would have it, to make this look right one has to be set up with common anode and the other common cathode. To make things even worse: the bargraphs have segments that are tied together. Here is a crude schematic:



.....S1............. S2........S3
O--|<]--O O--|<]--O--|<]--O

As you can see, segment 1 is all by its lonesome but segment 2 and 3 are tied together. I have more or less figured out how to drive them with transistors, how ever if you have been keeping up I have 6 12 segment arrays = 72 segments. thats alot of transistors. I have found a chip that will let me drive the common cathode array with no big issues, other than chip is not a latch. So in a nut shell, I have been able to get the common anode display to work, but it takes 12 I/O lines to do so not leaving very much left for lines on my little 16F189 chip. To further complicate things, My little pic is going to have to be handling an A/D pin (for fuel level input) and a pulse count pin (odometer count)

The chip I am using to drive the cc side is UDN2981. Basicly has a common supply voltage, common ground pin, and 8 line in going directly to 8 lines out (sourcing).

Question 1: Does anyone know of a similar chip used for sinking?

question 2: Does anyone know of a good serial to parellel latching chip that works with TTL logic? Probably 32 bits since I need 24 for each bar graph display.

bearpawz, Try an Allegro 6832. Attached is the data sheet...

Dave Purola,
N8NTA

If only they had that in DIP package for bread-boarding. I like to prototype my circuits on breadboard before going through the hastle of making a pcb. In fact, Ive got a few 6818's that are in plcc package, even have the plcc socket but its a quad socket and not dual so still hard to protype with out some sort of adapter.

http://www.mikroe.com/en/tools/plcc/...nboard_200.jpg
http://www.mikroe.com/en/tools/plcc/

Not sure it'll work with the Allegro chip though>
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bearpawz, Actually they did in the past. I have some of them and wanted to get some more but sometime yearly 06 they stopped making the 40 pin dip package. Darrel has a great idea. It could also be usefull for some of those plcc44 pic's as well.....

Dave Purola,
N8NTA

The max7219 can easily drive 64 leds. Not quite all that you need though. They come in dip packages and are pretty easy to interface too.