>I would suggest using some buffering, but it could be one chip, such as a
>ULN2003 (darlington array) or better yet, a LM293. I don't think a PIC can
>handle the current, and the back EMF would probably fry the PIC anyway.

There are unipolar and bipolar stepper motors. The unipolar is much easier
to drive, either ULN2003, ULN2803 (0.5 A), or ULN2064, ULN2068 (1.5 A) or
four discrete darlingtons/FETs will do. Unipolar stepper motor has 5 (or 6)
wires coming out.

Although bipolar stepper motors have some advantages, they are more
difficult to drive, since they need to reverse polarity on their coils. This
can be achieved with dual full bridge like the Thomsons L298. Bipolar
stepper motors have only four wires. If the motor has eight leads, then it
can be wired either as bipolar or unipolar.

I have learned a lot from Thomson application notes, I have a CD-rom, but
they should be on their web site as well (www.st.com). Namely the AN235 is a
good starting point, AN238, AN266, AN460, AN467-470 go into more details and
are targeted toward specific ICs, but will certainly answer more questions
than you wanted to ask. BTW, you don't need the L297 (mentioned in ANxxx),
the PIC can generate the driving sequences without any problem.

>For great deals on steepers, look up alltonics. They have a web page
>(www.alltronics.com). $3 each!

Or get a faulty/obsolete 5 1/4" or even 8" floppy drive and dissect its
guts, there is a stepper motor inside (in 3 1/2" drive as well, but it is a
smaller one, often build into the chassis and/or bipolar). It may be even free.

Josef

====================================================================
Snail Instruments                   Josef Hanzal
Vojanova 615                        phone/fax: +420-311-24433
266 01 Beroun                       e-mail: euroclass@pha.pvtnet.cz
Czech Republic                      URL: http://www.vitrum.cz/snail/
====================================================================