Is there any way to wire 2 steppers to a Raspberry Pi with a ULN2803 Darlington chip? (http://www.adafruit.com/products/970) Can you wire multiple ULN2803's with 2 steppers attached? Is there any way to do this with a minimal amount of GPIO? If so, how?
Almost certainly. Are they unipolar motors? Most of the hobby steppers I've seen come with driver boards containing a variant of the ULN2XXX.
Here a unipolar motor is been driven by a ULN2003A. The inputs are four Pi gpios. You'd need 8 for two such motors.
The software is trivial. The steppers should have timing diagrams to show the order to pulse the coils.
For last part of the question on minimum GPIO pins, use Shift Register. Need 3 pins (Data, clock, latch).
Traditionally, ready made chips are in the TTL family. Easy for up to a few tens of bits.
Modern varieties of "field-programming-chip" allow you to "design and make your own" (high number of bits, highly complex functions, etc.). Reading 100 pages book may get you started while in-depth application can be complex. If high data bit number shift register (use ready made chip for low bit number) is the requirement, be sure to choose suitable starter-level reading materials.
