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DPRG: Motor Divers

Subject: DPRG: Motor Divers
From: Kipton Moravec kmoravec at airmail.net
Date: Wed Jul 16 14:24:40 CDT 1997

ProMacPrg at aol.com wrote:
> Hi everyone!
>         It is me again, with yet another question.  This one I think is less
> involved then the last one about microcontrollers was.
> Does any one know of a stepper motor controller chip that can control a
> stepper motor that have 4 wires coming from it, I think it is called a
> bipolar stepper motor.  I don't know the current rating for the motor and the
> voltage is unknown also, but it is a small motor about 3/4 an inch in
> diameter and about 1/4 wide, if that helps at all.   The other part of this
> question is that I would like to bye the chip from either Mouser or Digi-Key,
> because I am going to be ordering other things from both of them tomorrow.
>  So does Mouser or Digi-Key sell such a chip?  I want to control the speed
> and the direction of the stepper motor using the Basic stamp 2 (which can
> give out about 10 mA at 5VDC) and the chip, with as few other parts as
> possible.  If Mouser or Digi-Key doesn't sell any of these chips does Jameco
> or Newark?  Those are the only other catalogs that I have right now.
> Thanks a lot,
> Timothy Deterly
> ProMacPrg at aol.com

Stepper motors have their good points and their bad points.  The good
thing is that it gives you a way to measure how far you have gone (if
you keep track of the step count), and they have a very good break, They
stay in the position. Speed control is also easy with a stepper.

The bad thing is usually there is never enough documentation on the
cheap ones <grin>. With DC motors it is simple. Hook it up and see it
go.  If it does not work right, switch the polarity and you are set. 
With Steppers you have to decide how many windings there are and the
step sequence.

Usually there are two or four windings. Based on the brief discription
you gave, I would guess there is two windings. That means there are not
that many combinations for you to wire wrong! <grin> If you take an ohm
meter, you can tell which lines match up to a winding. Probably line 1
and 2 are one winding, and 3 and 4 are the other.  Sometimes they have
the windings share a common ground. For example my stepper has 4
windings, and 5 wires instead of 8.

Fortunately there are not that many parts to make it work right. Most
are built for 4 phase steppers and you probably have a 2 phase stepper.
I would recommend keeping it controlled by your microcontroller.  There
are two approaches, one with relays and one with transistors.  If you
choose to do the relay route, you will need 2 SPDT relays, 2 2N2222 npn
transistor, and 2 1K 1/4 watt resistors.  The transistor approach will
need 2 TIP120 npn Darlington transistors, 2 1N4004 diode, and 2 1K 1 W

How do you decide which approach?  You will need the relays if the
stepper motor needs negative voltage.

Example for each winding.

- -6 VDC -----------------------o---v
                                  v---- to winding (other end of motor 
+6 VDC ---------o-------------o---^            winding goes to ground)
                |---------------3 ||
                                3 || Relay 
                            ----3 || Magnet
                        b |/
Phase      o-----/\/\/\---|    2N2222
Control            1K     |\
                            | e

If the motor does not need -6 VDC (or whatever voltage the stepper
needs), then you can use a simple transistor arrangement. 

                      +6 or +5 to +12
                       __|__     3
                         ^       3  Motor Winding
            1N4004     _/_\_     3
                         |       3
                        b |/
Phase      o-----/\/\/\---|    TIP120 npn Darlington transistor
Control            1K     |\
                            | e

Circuits in ASCII are difficult. :)

Phase Sequence for two phase stepper.

Step        Phase 1         Phase 2
 1            Off             Off
 2            On              Off
 3            On              On
 4            Off             On

I got all this info from "The Robot Builder's Bonanza, 99 Inexpensive
Robotic Projects", Gordon McComb, TAB Books, 1987



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