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DPRG: Motor Divers

Subject: DPRG: Motor Divers
From: Jim Brown jbrown at spdmail.spd.dsccc.com
Date: Fri Jul 18 14:31:57 CDT 1997

 
> fellow stepmotor users:
> 
<snip>
>
> So, I offer this simple alternative:
> 
> Use a ULN2803A. ...
>
<snip>
>
> It's as easy as it looks.
> 
> Jim: You're welcome to put this in the DPRG faq.  What?  You don't have 
> one yet?  Well, here's the first article.

I'll try to add it to the DPRG Faq along with Eric and Kip's emails.
It's slim pickens so far, but it can be found at:
http://www.dprg.org/dprgfaq.html

Oh yes!  Since I found out your little ULN2803 (or 2804) trick, I've
been in stepper paradise.  It's really is a nice way to go.  I've gotten
the ULN2804 version at Tanners!  Works practically the same as the 2803
but available at Tanners.  I think they were .50 or 1.00 or something
like that.  Well worth it!!!  And the circuit makes sense!  One can drive
two steppers from one 2803 (or 2804) chip.

         +5v              
          |    _________    +-----------------+--- +12v
+-------+-+   |       10|---+     _________   |
| 8051 1|-----|1 2803 18|--------|         |  |
|      2|-----|2      17|--------| stepper |  |
|      3|-----|3      16|--------|         |--+
|      4|-----|4      15|--------|_________|  |
|       |     |         |                     |
|       |     |         |         _________   |
|      5|-----|5      14|--------|         |  |
|      6|-----|6      13|--------| stepper |--+
|      7|-----|7      12|--------|         |  
|      8|-----|8      11|--------|_________|  
|       |  +--|9        |                    
+---+---+  |  +---------+                   
    |      |                           
    +------+-----gnd


Each of the 8 buffers in the 2803 has a incoming resistor, 500ma
sink, and a flyback diode.

                        +12
                         |
                      +--+--+  
                      |     |
                      |     _
              1k      |     ^
                      |\    |
to mcu  ----/\/\/\----| >---+--- to stepper
                      |/ 
                      |
                     gnd

I think the only difference between the 2803 and the 2804 is that
the 1k resistor in the 2803 is a 10k resistor in the 2804.

These 2803's work great for unipolar steppers.  For the bipolar ones,
I'd probably resort to a nasty stepper chip or just switch
to a unipolar stepper.

Unless a stepper is the only thing that will work,
I'd now choose to use a servo if possible.  There's no
glue logic to hook to an mcu, and inherently you'll know what position
the shaft is in (unless something is malfunctioning or under great
torque), unlike a stepper that you'll need feed back.  Plus, a servo
only needs one I/O line!  Most servos won't go beyond 180 degrees, but
for most things that's perfect.  Most things that need to rotate don't
need the kind of accuracy that a stepper will give.  In that case, I'd
use a DC motor and an h-bridge.  Unless you're making a dot matrix printer
or something that needs that sort of accuracy, I'd stay away from
steppers.  They have too little torque, they're complicated,
and they use lots of precious i/o lines... but they do have
accuracy.  If you need positioning, but super accuracy is not an issue,
a servo would be my choice.

- ---------------------------------------------------------------------------
Jim Brown                jbrown at spdmail.spd.dsccc.com or jbrown at why.net
                         http://users.why.net/jbrown  
                         http://www.dprg.org (Next meeting July 12th)

Work:  972-519-2868      My employer won't claim these opinions.    
Home:  972-495-3821      So I'm giving them away for free.   

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