Alt-BEAM Archive

Message #00739



To: richfile@rconnect.com, beam beam@corp.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Sun, 21 Feb 1999 12:29:07 -0800
Subject: [alt-beam] Re: stepper motors




S'allright Rich! The MicroCore has complementary outputs (active high
and low) so doesn't need the Rbe. If you drive your transistor buffer
from an open collector or tristate device you do need it. I suggest
using 2N7000 N channel Power MOSFETs ($0.50 ea) transistors with an
"upside down" MicroCore since you can then use a high voltage (12V)
supply for the stepper windings (fig 3). This circuit is good for small
steppers requiring less than 1A. I mean is anybody actually interested
in this? (arrgh! maybe I'm not getting enough sleep)

You may want to point out that the MicroCore Stepper Circuit only does
"unipolar" steppers. These have 4 windings generally connected together
at one common end and so have 5 wires (fig 1). Sometimes unipolar
steppers have 6 wires which means 2 common leads (fig 2) which should be
tied together. Use an ohm
meter to identify leads and play around with the sequences.

With one process in MicroCore, the outputs go through what is called a
"wave" step sequence. After starting the microcore process with the
usual PNC, you can stop the process (and stop the motor) by opening
switch S1 which applies Vcc/2 to the common point for the 4 microcore
resistors. This puts the Nv neurons in the memory mode (I have
previously explained the operation of this ETC terminal for a microcore.
In fact it was my first article to this list). With the switch closed,
the common of all the resistors (ETC) is connected to Vcc and allows the
microcore process to continue.

Depending on the number of poles in the motor, the rotation of the shaft
is 360/poles=degrees/step and the numbers of steps required for a full
rotation is 360/degrees/step steps. (I think I got that right). A
bicore
(240 or 14) master-slave with it's quadrature outputs should be able to
handle bipolar steppers. I believe a reversing bicore may reverse the
rotation but I haven't thought it through. Maybe I'l post a GIF of the
full circuit.

coil
1------/\/\/\/\--|
2------/\/\/\/\--|_____ 5 (common)
3------/\/\/\/\--|
4------/\/\/\/\--|


FIG 1 - 5 WIRE UNIPOLAR STEPPER MOTTOR WINDINGS


1------/\/\/\/\--|______5 (common 1/2)
2------/\/\/\/\--|

3------/\/\/\/\--|______6 (common 3/4)
4------/\/\/\/\--|

FIG 2 - 6 WIRE UNIPOLAR STEPPER MOTTOR WINDINGS


Vcc
|
S1 / START/STOP
/ SWITCH
|
Vcc--[10K]--[10K]--0V
|
to | coil 1
R2-4 <--| 1 +------/\/\/\/\------ 5 +12V
[R1] |
| __ |__|
____||__|_|14 \___________ |
| || |__ / | `----|<-+ 2N7000
| C1 | |__|
v v | |
|
to other Nv stages 0V

FIG 3 UPSIDE/DOWN MICROCORE STEPPER WITH START/STOP

IMHO there are hints here (together with Dennison's "invisible Nv's) for
interfacing microcores to MPUs
(let's see if this nudge gets anywhere).

enjoy

wilf

-----Original Message-----
> From: Richard Piotter [SMTP:richfile@rconnect.com]
> Sent: Sunday, February 21, 1999 7:31 AM
> To: beam
> Subject: Re: stepper motors

> As i said, I took i from my digital electronics book around 12:00 AM.
The
> basic
> schematic will work, throw any reasonably sized transistor in it's
place
> and you
> have a driver. I suppose the book assumes your driving a tank made
with
> stepper coils.
>
> I would assume most people would just throw in a transistor in it's
place
> and
> leave it at that. I saw why they put the pull up resistor in the
whole
> circuit.
> So maybe the microcore doesn't need it!
>
> Try this then.
>
> +5v
> ___
> |
> |
> |
> |
> |
> /
> 470 |<' 1N4001 or equivalent
> o---/\/\/-------| ,------|<-------.
> from |\ | |
> microcore `---o--o to coil o--o--.
> PNP |
> transistor _|_
>

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