At 12:13 1998-03-17 GMT, you wrote:
>Morgan,
>
>I wrote:
>> >Hi,
>> >
>> >I want to control two 2-phase stepper motors (bipolar) using a PIC
>> >16c71. Does anyone know how I can do this? ie how do I connect the
>> >phases to the output port to change current direction, transistors to
>> >use, etc. Please note, I am constricted by space - this is for a one
>> >cubic inch microrobot.
>> >
>
>You replied:- 
>
>> National Semiconductor 74AC04 Hex inverter can supply I believe 60mA per
>> inverter if i don t remember wrong. Available in SMD.
>> Check their data (NSC AC04 is stronger than other brands AC04 !)  8)
>> Tell me if it works!
>> /Morgan
>
>More questions:- 
>
>How do I connect the inverter to the motors - I have never used them 
>before. 

If full step only:
Inverter A input fron PIC output to winding 1one side, and next inverter,
output from next inverter to other side of winding.
Same setup for other winding= total 4 inverters (AC04 contain 6!) and 2
pins from PIC. Problem is you always have full power on.

For half step: 
One pin from pic to inverter, inverter output to winding.
The same for other side of winding.
Other winding as above.  Really nice and simple, isn«t it?
Advantage: lower consumption when only one winding genergized, no power
(and low holding torque) when 
Misadvantage: uses 4 pins from PIC.

Probably you have to parallel inverters two or three to get the power and
low loss. Use one AC04 for each winding?  Do not forget capacitor close to
AC04 Vdd and Vss Ceramic multilayer 220n is still physically small.

Reason AC04 is not commonly used are:
1) It is on the edge of specification, or you have to be careful
2) Very fast transitions=noise spikes; take care about "layout"
3) Possibly oscillates due to sensitive input and fast strong output.

>Also, if I used my bipolar stepper motors in unipolar mode 
>would there be a large drop in torque? I was told generally about 20% 
>drop -is this accurate?

On top of my head, I think that is accurate (depending of motor and
driver), but you then also have double current consumption, not at all good
for your application!

And i can not think of a unipolar drive that is smaller than above!
Regards
/Morgan

>Dav

Speaking of very small steppers, I was once thinking of using a
electrimechanical watch mechanic.  A complete servo with stepper motor and
gears can be extracted!  "Just" exchange the winding.  It would be weak and
slow, but I only wanted to make sub-gram remote control for ultralight
indoor airplane.  Never had the time, though...  And that was ten years ago
when i did not find any microcontroller or reciever cirquit small enough,
but now there is!

Tell me how You proceed!

Regards
/Morgan

/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  mrt@iname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /