Homebrew PCBs

Robert Hedan wrote:

> Darn,
> 
> It seems the circuit I had for unipolar steppers can be wired for bipolar
> steppers as well.  I found a copy of it here, but there's just one problem:
> 
> Figure 9.1: http://eio.com/jasstep.htm#translators
> 
> "I think when you reverse direction and continue stepping, the motor will
> advance 1 more step in the previous direction it was going before
> responding."
> 


   That is "bi-directional", as in turning the motor both ways, vs only one way 
in the circuit above it.  Have to keep your 'bi-'s straight, nothing to do with 
running a bipolar motor, that takes two full H-bridges as in his fig 6.1.  Stick 
to unipolar until you have a better handle on what you're doing, bipolar has 
advantages but you don't need them to start and it takes twice as much to drive, 
plus other problems in the driving.




   Also note that anyone can read a few other people's web pages, draw up a 
circuit or two, and look like they know what they're doing in five minutes. 
Says more to their web page creation skills than anything else really.  7486 is 
typically a 5V chip.  The upper transistors will only pull up to 5V, with more 
power wasted in them than making it to the motor with a 12V supply.  In other 
words a crap draw up, likely it was copied from somewhere else with changes and 
only a partial understanding of what's going on.

   While 90% of the info on most of these basic stepper motor type web pages is 
correct, 90% or more of them also have a notable error or two.  It's easy to get 
the basics and make a web page, but relatively few of the people who do that 
tend to have a good understanding before they make their pages.  Don't count on 
any of them being 100%.

Alan