Driving stepper motors / schematic comprehension help

http://www.eminebea.com/content/html/en/engineering/motors/pm_motor/selection_pm/drivecircuit.shtml

See if this kids course doesn't help:

     http://www.taomc.com/bits2bots/index.htm

I believe they used BASIC print commands to move their stepper ...


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Thanks for your response!  That site looks really helpful.  I'll check
it out.

You didn't actually read my post, did you?  The site you referenced
specifically uses a ready-made IC to convert signals to drive the
stepper motor.  My question is, given the stepper motor that I bought,
do I need to use a similar chip myself.  Or does the schematic
described in the following link:

http://www.eminebea.com/content/html/en/engineering/motors/pm_motor/selection_pm/drivecircuit.shtml

... prove sufficient.

Thanks again!
Adam

NPN transistors (NOT POINTING N)

-+-

base is +, collector and emitter are -

so, a small positive voltage on base (the flat line sticking
to the left)

causes voltage to flow from the emitter (the lead with the
arrow that is NOT POINTING IN) to the base

this biases the transistor, and will allow collector current
to flow through the emitter...

so, small positive voltage on base (control) ends up giving
your stepper motor GROUND (negative)

Gotcha...  I guess I expected "ground" to be a wire coming out of the
whole system.  It appears from the schematic that there is some sort
sort of "internal ground".

That is, if I apply a control signal to the base of one of the
transistors, the current flows from the source, through the coil,
through the transistor, and into the internal ground... ?

I think we're on the same page.  thanks so much for your reply!

Adman

Not "internal ground"... just grounded to the case...  there is
probably
a terminal on the case, or a terminal on the PCB that ends up being
connected
to all the appropriate spots (places in the circuit where "ground" is
needed")

The NEGATIVE side of the parallel port (GND) would be connected to
the
GND of the stepper controller...  this flows to the "little black
boxes" you see
in the schematic.

ground is shown as a block, or often as a T with reducing width lines
on top:

(view with monospace font)
.._..
.___.
_____
..|..

The reason:  to clear up the schematic.  a ground symbol means
"connected
to negative side of power supply".  If you had a schematic with all
the grounds
shown, they end up crossing over all of the positive lines, and the
schematic
ends up being very hard to read.

Rich

No, the drive circuit is not part of the stepper.

All I see on the spec sheet is the "Drive IC" as 2SC3346 which seems (when
I look it up on the internet) to just be a a high power switching
transistor you could use to build a drive circuit.  I read that as just a
suggestion of the type of drive circuit you could use to drive it.

If the stepper actually included a drive circuit, it would give you far
more detailed specs on the drive circuit instead of just listing the part
number of a single transistor.


No, that's not how I read it.

The transistors and diodes in that schematic are NOT part of the stepper.
They are just shown as a _typical_ drive circuit and how you would connect
a _typical_ drive circuit to the stepper.  The wires coming out of your
stepper will be the black, red, brown, etc writes connected directly to the
coil.

You still need to buy or build some type of drive circuit because the
signals on your parallel port do not have the right voltage or current to
directly drive your stepper.


That's right in theory.  But you have to get the voltage and polarity and
current right.  That is, the drive circuit you end up using has to be
compatible with the signals coming from your parallel port.  In that
schematic, which uses NPN transistors, you would have to apply a positive
voltage to the base to make the transistor "turn on" and a ground (or
negative, or just open) to make the transistor turn off.  The parallel port
would need to supply enough current at a positive voltage to make that
work.  "enough" will be a function of the amplification of the transistor
(it's beta) and the current you need to drive the stepper.  I don't
remember how parallel ports work, but you might need something like a
pull-up resistor in there as well.  Which is why it's best to just buy a
drive circuit designed for working with a parallel port or to find a
schematic of one for your need and build it if you want to have fun
learning to do that.

I'm sure you can get some suggestions here on where to find a drive circuit
for your needs.


That's just a generic symbol which means ground.  It's where the negative
of the power source driving the coils are connected.


It doesn't have it's own internal circuit.  You do need to build or buy a
drive circuit.  I've never played with these so I don't have any
suggestions on what to get, but I suspect you can find one made to be
driven by a parallel port - lots of people do that.  Or at least they used
to back when all PCs had parallel ports. :)


--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/

I suspected this myself but wasn't absolutely sure. It looks like
circuit Adman provided the link to is really just a generic diagram
showing what the external circuitry might look like (without values,
resistors, etc). It is not a circuit actually provided with the
stepper motor.

The part you are buying is indicated on the drawing by the dotted line
box, which indicates what part of the diagram is the actual motor you
are purchasing.

Joe Dunfee

Great.  Thank you all very much for your comments.

    1985 called.  It wants its PC/AT back.

                    John Nagle

Here are 2 great books to get you started:
1) Google for "Parallel Port Complete" and you can see most of the book online.
2) Google for "Controlling The World with Your PC" to see much of it online, too.

These are both old enough to be found in libraries or very cheap online.

also, here's a nice page: http://www.doc.ic.ac.uk/~ih/doc/par/

Good luck!
JCDeen

http://electronics-diy.com/electronics/stepper_motors.php

This doesn't look that complicated.... right?

So far, you haven't actually told us what you want to do
with the stepper motor.  Stepper motor control can range
from really simple to rather complex depending upon the
application.

For the simple stuff, the key is not to exceed the coil
current for the stepper motor and/or driver circuit.
The stepper motor spec. sheets rarely specify the maximum
coil current.  They do specify a nomial voltage and (sometimes)
a coil resistance.  If the coil resistance is not specified,
break out a volt/ohm meter and measure it directly.  Use Ohm's law
to find maximum current.

   Voltage = Current x Resistance

For the drive circuits, some of them have protection diodes
built in and some do not.  Make sure that all components in
the drive circuit are rated for the specified current.

For beginners, I recommend using drive circuits that are
designed for driving inductive loads, rather than building
them from individual transistors and diodes.  The L293D
has protection diodes built in and comes in a 16-pin DIP
package.  The SN754410 is a more modern equivalent for the
L293D.  For a higher current, the L298 is good device, but it
needs external protection diodes.

Everything starts from the current requirements of the
stepper motor.

-Wayne