RJT> I remember something I learned from studying the service manuals of Okidata
   > printers,  particularly the 82/83 series and the 92/93.  The two numbers in
   > each pair are just standard/wide carriage.  The differences between these
   > models is minimal,  but also involves speed.  They achieve the speed increase
   > in the later design by using a 10 volt (?) supply to the stepping motors on
   > continuously,  as appropriate for the given phase of the motor. 
But when it's
   > moving,  they *pulse* it with something like a 30 volt supply --
which I'm sure
   > gets its attention...    :-)

RJT> There's even a failsafe in there.  Steering diodes keep the stuff separate, 
   > and a little monitoring circuit looks at that higher voltage line.  It has a
   > monostable in there.  If that voltage is pulsed,  all is fine.  If for some
   > reason it stays on,  the chances are pretty good that motors and
stuff will get
   > damaged,  so at that point a crowbar circuit kicks in and blows a fuse.

RJT> Kinda nifty design,  I thought.

Much more efficient than the old series resistor trick, I'm sure. It's 
handy as a quick and simple solution, but there are definitely much better 
ways to do it, as you've just described.


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