I read a lot of DIY hardware blogs. A common thread is how best to run an LED matrix with the best balance between performance and pinouts.
The lamp matrix of the pinball machine is the exact same problem. Traditionally the lamps in the machine would be a bunch of #555s, #44s,#906s etc. Being a greenie at heart, I'm going to replace the lamps with leds. There are a lot of nice writeups out there discussing the retrofit of existing machines, and vendors have even started to produce LED plug in replacements for the old standard bulbs.
I haven't completely decided quite how to take this on. The choices boil down to:
Use the I/O driver board and drive the lamps.
Wire up our own LED driver board as a lamp matrix replacement
For a project like the re-skinning of my Goldeneye the plan all along was to use the already in place I/O driver board for all of the lamps, flash lamps and solenoids. Thing is, these cost $300 (in the wild) and have significant limitations that really beg the question of whether we should be just fabricating our own. Now that I have evicted the Sega CPU board from the mix I have been running through a bunch of scenarios for the pinouts of the new CPU board. I am leaning more and more away from driving the lamps through the Sega I/O driver.
Here is my favorite answer to running a 64 bit lamp matrix with the best balance of pins and power. The MAX6951. With this one chip, you can drive a constant current 2.7V-5.5V to 64 discrete LEDs with just 3 pinouts from your controller. Yes, it costs $15, but this chip does exactly what I need it to do without me needing to monkey together a bunch of additional chips and components (which is not my strong suit). I recommend spending time with the data sheet for this chip even if you don't decide to use it just to see how they solved the problem of driving a 64 bit matrix with 9 pins.
For the pinball application, I will be ordering and playing with the MAX7221CNG which is a 24 bin DIP version of the driver that will be easier to prototype with and a bit cheaper. I'll be ordering up some 555 and 44 LED replacement bulbs as well.