At 09:14 1998-03-10 +0100, Josef Hanzal wrote:
>>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, 

Better efficciency, lower consumption for same hold force, lesse dimension
and heat.
... Well it«s all the same.  All because the winding usage is more efficient.

>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. 

Ericsson PBL3717 and sisters are very neat.

>Bipolar
>stepper motors have only four wires. 

Six wire bipolar are also common. They can (i believe) also be connected as
unipolar.

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
>
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