Thanks for the schematics. That was really great that you took the time to draw those for me. What do you think of this though, where I only use one resistor and one transistor on each anode. Here is a drawing of a similar set up that I found, but this board seems to have common anode rather than common cathode (which is what I think I have). I'd like to apply this design to my project if possible. Obviously I'll be connecting vcc to resistor to transistor to each of the 12 anodes instead of the two as shown. Do you see any problem doing this?


Also, on this image you can see there are resistors between the cathodes and the micro. When I've interfaced an LED before I've just had a resistor on the cathode side (vcc to resistor to cathode) and then the anode was connected directly to the micro. Any reason I shouldn't do that here?

Lastly, I'm a little confused on common cathode and common anode displays so it is possible that I'm not stating what I have correctly. To be clear the only way I can get a segment to light up is if I connect what I understand to be one of the two ground connections on the display board (what I'm calling cathodes) to the negative terminal on my power supply (which is what I usually connect to pin 20 on a 40 pin DIP 8051) and I connect what I understand to be one of the 12 positive connectors on the display board (what I'm calling anodes) to the 4.5v line on my power supply (what I normally connect to pin 21 on a 40 pin DIP 8051).

If that was hard to follow:

On my 8051 AT89C55WDP:
pin 20 is ground
pin 21 is vcc (4.5v)

I connect "ground" to one of two spots on the display board
I connect "vcc" to one of 12 spots on the display board

then a segment lights.

Looking at your diagrams it seems that you've designed the circuit for a board with two anodes and 12 cathodes. I think that what I have is 2 cathodes and 12 anodes.