I have a project that is going to require a lot of IO. The program is actually quite simple and the PI can definitely handle it. But I need a LOT of IO. So here's the question:

Is it possible to use 3 IO PI Plus boards AND 1 Expander PI, AND still have access to the PI's 17 IO? From what I've been able to gather I can only use 2 IO PI Plus and 1 Expander or 4 IO PI Plus. There are ways I can make this work with a single RPi if the expansion boards will cooperate.

1- 3 IO PI Plus + 1 Expander PI + RPi 17 pins

2 - 4 IO PI Plus + RPi 17 Pins and some A/D circuitry on a couple of the pins.

I can reduce the number of discrete inputs by using more analog inputs but I'm hitting a wall there as well.

Ideally what I need is 64 discrete inputs, 56 discrete outputs, and 3 analog inputs, but I have some flexibility with the inputs. In some places I can substitute 1 analog input for 2 discrete inputs (travel limits) by using a motor with encoder or fitting the mechanism with a POT for position feedback.

Anyone know of a way to get that many IO from a single RPi?