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Posted by Curt Welch on March 29, 2008, 10:56 am
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> Hi all... I'm a software guy trying to learn the ropes of electronics.
>
> I have the goal of controlling a stepper motor using my PC parallel
> port to create +5v control signals. Shouldn't be that hard, right?
>
> My understanding of 5-wire stepper motors is that there will be one
> common power wire, and four other wires coming out. Attach the power
> wire to the power source, and attach the other wires to ground (using
> some logic to connect the right ones to ground at the right time), and
> you're all set.
>
> I bought a unipolar stepper motor... the first one listed on this
> page:
>
> http://www.futurlec.com/StepperMotors.shtml
>
> One thing I noticed is that the spec sheet lists that it has a "drive
> circuit".
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.
> Some more investigation led me here:
>
> http://www.eminebea.com/content/html/en/engineering/motors/pm_motor/selec
> tion_pm/drivecircuit.shtml
>
> Since I bought a unipolar stepper, I think the first schematic on the
> page applies. I'm not quite sure how to read it. It appears that
> what I want to do is attach my parallel port data pins DIRECTLY to the
> bases of each of the transistors (which is what the four non-power
> wires coming out of the motor will be).
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.
> If that's the case, it looks like I use my parallel port control
> signals to activate each transistor according to activate the internal
> electromagnets in the proper order.
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.
> Being a smart software guy, I can
> handle that. When I do that, the power will go through the coils,
> through the transistors, and into the little black boxes.
>
> What are those little black boxes? Some sort of internal ground?
That's just a generic symbol which means ground. It's where the negative
of the power source driving the coils are connected.
> Sorry for the newbish questions, but every description of a unipolar
> stepper motor seems to imply that I need to build or buy my own drive
> circuitry. So the idea that this one might come with its own already
> built right in is throwing me for a loop.
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. :)
> If someone could confirm my suspicions, or point me in the right
> direction, I'd appreciate it.
>
> Also, I don't actually have the motor in my hand yet. It's being
> shipped. I'm just trying to get things figured out before it gets
> here. :)
>
> Thanks!
> Adman
--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/
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> > your stepper motor GROUND (negative)