Wednesday, October 04, 2006


How to build a simple XY stepper controller (Unipolar)

As promised, here's the information you should need to interface 2 stepper motors to the computer, via the printer port.

The main part of it all is the ULN2803. It is a beautiful little 18pin IC that can plug directly between the printer port and the steppers. I don't know what they're rated for, but I've pushed ~20v through it onto NEMA 17 steppers for several minutes without too much heat. If you were driving steppers the size of a soda can though, I would use 2-3 with heat sinks.

You can power it with 5 or 12v. Note in the second image I only used the 1st chip. I plan on upgrading later for the 3rd axis, but for now, just forus on M1 and M2.

As you can see, pretty simple. The interface below can be made in a few hours, with a bit of skill.

The printer port connecter was bought at radio-shack, and the pinout is as follows:
Datalines 1-8 = Pins 2-9 (top right)
Ground line = Pin 22 (4th pin from the bottom left)

The test program used was made in VB6 (because I'm old-school), and uses a library called inpout32.dll for low-level interface to the printer port in Windows XP. I am talking with Plaasjappie to see if he can leave a copy on the server. It is a very basic and hacked-together, as I'm still looking for other cnc programs that might work with this setup, and I'm not much of a programmer myself.

Good luck, all


You can link to Reiyuki's VB programmes via...


...for now.
You just had to wait to post this until after I put in my order for more electronic components... didn't you?

Being certified,(insane that is...) I'm integrating my reprap directly into my pc... and I've been pondering this little gem:

It's got 72 i/o points... so I'm wondering if the pc could drive everything through software, via that card, into a simple board (ie: ULN2803), instead of making the 'complex' 'ring network' controller boards we've currently got designed...

I'm guessing that this should be able to do whatever you could do with a printer port (so it could run the 3 motors), and the only thing I see causing a problem with controlling the extruder is any lag/latency (specifically for temperature control)

(damnit! there's gunna be shrinkwrapped repraps on the shelf at computer stores if I have to put them there myself!)
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