I have a project I'm starting on, which at the core is a clock. To prototype, I'm just using a Teensy++ on a breadboard, so I'd like to start with some small off the shelf 7 segment displays (at least 6 digits). Eventually, the final project will require large (at least 6 inches, and maybe 12 inches tall) digits, as I'll need to be able to see them clearly from at least 100 feet away (these may wind up being a custom part I make with a *LOT* of LEDs).
For now, I'm trying to figure out the best way to drive a bunch of these displays. Here's a few generic ideas I've found...
1) Multiplexing. It's the cheapest, all done in software, and most power efficient, but I'm not sure if it will scale well to the larger display, as that will definitely require a separate driver. Also, it may take up too much CPU time, though not certain.
2) Latches. I'm not hurting for I/O pins, so I could just set up some pins (a quick calculation suggests something like 16 pins total) and just use the latches to drive the displays. This is pretty simple, but it requires 8 latches per digit, which winds up being a lot of hardware.
3) SPI/I2C driver. Doesn't require a lot of I/O pins, though maybe a bit more CPU time. The driver shouldbe able to drive the prototype directly, or hook into a higher powered driver for the larger display.
4) Other ideas...?
I'm leaning towards using SPI/I2C driver, as I think that's probably the easiest. If I do that, then I can use something like this http://adafruit.com/products/879 for prototyping, and then if I build my own driver for the larger display, just copy the I2C commands. I'm not sure if this actually makes sense though, or if there is a better way to do this that I'm totally missing?
FYI, this will be mounted on a wall with external power, so power draw is not a concern (within reason, I don't want a nuclear power plant to run this thing :lol:). There will also be a Wiznet (or similar) SPI ethernet adapter, and probably an SD card on the SPI bus as well.