Arduino pulse voltage?

[pgang]

Hi,

I'm setting up a CNC router with an Arduino Uno connected to pretty standard bipolar stepper drivers powering NEMA 23 motors. Still in the testing phase, none of my motors will move in a positive direction, negative only.

The direction pin is giving me good voltage readings, changing from 5V to 0V as required. However the pulse pin seems a little odd. In a negative direction (for a single step of 1mm) it reads about 350mV, but +ve is only reading about 150mV. Is that normal?

The only other thing I can think of doing is to increase the $0 step pulse.

Any ideas???

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[pgang]

I think I might have solved the problem. When I bought my drivers I went with the peak amperage rather than the RMS (and of course bought the cheapest possible within that boundary). My motors draw 2.8 amps per phase, and my driver's peak output is 3.2A with an RMS of only 2.3A. Doh!

Time to order some new drivers...

[hfjbuis]

Your driver should be able to run that stepper allmost on full torque. So the problem must be something else!

Normaly with just the pulse pin and +5V or Gnd connected , the stepper should turn.
$0 should be high (long enough depending on your driver. You can't set it higher than about 70. Set it to 50 just for testing. A value of 10 will do for most drivers

Disconnect the enable and direction pins.
Connect the Pulse (+) pin to 5 volt, you could do manual stepping by connecting the Pulse pin (-) to gnd and then disconnecting it.

The pulse and direction pin should have the same voltage swing levels. But if the pulses are send, it is hard to measure using a voltage meter. You need an oscilloscope to see the levels.

[pgang]

The original drivers had no ground circuit (apart from power), and enable was bypassed by default. They were pretty basic. While the motors worked ok in one direction, they wouldn't turn in the other, but made a slight whistling sound. Perhaps this was due to the lack of a ground circuit, but seems more likely to have been that there was insufficient driving current. Why just in one direction I don't know. I tried various hookups with the same results.

Anyway once I hooked them up to larger drivers with appropriate current output (and ground circuits on PUL and DIR), they worked fine.

[skrubol]

I think the problem was current, but not where you're thinking. My guess would be that the old drive had a really high input current requirement on the inputs, and the Arduino pins weren't able to drive that. That's why you were only seeing 150 and 350 mV where you should have been seeing 4+V.

[pgang]

Interesting point. I too am having my doubts about my original theory. Reduced current should reduce the operating output, not remove it entirely, especially under no-load conditions. Clearly there was enough current to operate the motor in one direction - so why not in the reverse direction?

So yes, it sounds like a control issue, rather than a motor current issue. I also suspect that the lack of a ground circuit on the driver's pulse and direction pins may have been part of the problem, although I don't have the electronics knowledge to say why. The drivers had +ve connections only, for pulse, direction, opto and enable. A strange arrangement.