I am working on a project that has exhausted most of the pins on my Netduino 1. I only have D2 and D12 now available. I would now like to drive several 7-segment LEDs. I realize that there are drivers out there that can accomplish this, but all that I have found require a 4-wire SPI. My question is this: What options are available to me to add an additional 'duino board (wether that be another Netduino, or Arduino), using only those digital pins that I have left? If I can hand off control of the LEDs to an additional microcontroller, that would be perfectly acceptable. I basically just need to pass a single digit to each of 8 7-segment displays.
Ideas are welcome. Thank you.