Hello Guest it is October 18, 2019, 06:07:46 AM

Author Topic: Low voltage on 'step' pin  (Read 4496 times)

0 Members and 1 Guest are viewing this topic.

Offline Lubby

*
  •  25 25
    • View Profile
Low voltage on 'step' pin
« on: March 03, 2015, 01:20:10 PM »
I can seem to find this issue answered elsewhere on the forum.  If it has please let me know.

The issue:
I have a second parallel port setup for a fifth axis ( axis A ) via a stepper driver ( st330-v3 ). 
The configuration: Step, Pin 2;  Dir, Pin 3;  5+ for board via ChargePump2, Pin 16;  All on port 2.
ChargePump2 works ( 4.9v supply to board )
Direction works ( inactive = 0v, active = 4.9v ) 

!! Step Voltage does not.  When inactive = 0.03v and when active = 0.09v

Stepper chatters but does not move when Dir Active.  Does not chatter or move when Dir Inactive.


What I've tried:

I've check the stepper driver with an arduino.  The PWM and Dir work fine.  It is not the motor or the driver board itself.
I've tested the pins on port 2 by putting the spindle PWM on the pin I want to use for the step.  Then I can get a reading of 0-5v depending on the speed I set the spindle to.  It is not the pin or the PCI card.
I've tested the A axis motor tuning and setup by applying them to a different motor and driver (Gecko G540).  That motor moved fine.  It is not how the motor tuning is set up.
I've tested the uS pulse?  No difference.
I've tested the motor at different feedrates?  No difference.


I'm at a loss.

What could be preventing the pin set to A axis step from going to 0V when inactive? ( it is inactive at 0.03v )
Why is it that this pin only reaches 0.09v when active.  When testing with spindle PWM it is not an issue?
Why would the motor tuning work on another motor and driver and not this one.  The motor driver works with arduino?

It's not a hardware issue as I've tested the motor, board, and pins.
What am I missing?

I'm sure it's a bit difficult to offer a simple answer to this but any suggestions on what to check or test would be appreciated.

thanks




Offline Hood

*
  •  25,855 25,855
  • Carnoustie, Scotland
    • View Profile
Re: Low voltage on 'step' pin
« Reply #1 on: March 04, 2015, 03:44:51 AM »
The likely reason you only see a small voltage change is the active Hi/Lo setting and your pulserate.
Have you double checked that you have the Step and Dir wires connected the right way round? If you inadvertently had the Step pin connected to the drive Dir input then it would be getting fast pulses instead of a steady 5v or 0v.

Hood

Offline Lubby

*
  •  25 25
    • View Profile
Re: Low voltage on 'step' pin
« Reply #2 on: March 04, 2015, 06:55:42 AM »
Thanks Hood.

Yes I had double checked the DIR and STEP wire to ensure they're not mixed up.

I considered that the low voltage might be a reflection of a low pulse rate.  The things is that the voltage doesn't change with a much higher change in feedrate or (steps) within motor tuning.  I also tested the port pin by putting the spindle PWM on it.  Then the PWM works fine and reflect the speed of the spindle.

I did also try sending the STEP pin to another pin on the port.  Same issue there.  This make me think it's not the hardware (it can put out a PWM) or the pin setup but that it's somewhere else in how things are configured in Mach3.  Motor tuning? 

Yep, totally lost on this one?

I may try things on another driver but I don't think that will make a different if I can't get the voltage.

Offline stirling

*
  • *
  •  2,188 2,188
  • UK
    • View Profile
    • www.razordance.co.uk
Re: Low voltage on 'step' pin
« Reply #3 on: March 04, 2015, 11:29:47 AM »
Not sure I can help but here's a couple of thoughts as I read through your posts.

Powering a BOB from the charge pump signal? You sure you can do that? I never use the chargepump signal but I'd have thought the BOB would require more current than a pin can source.

You don't say what you're measuring the voltages with but your step signal can't be measured with a multi-meter for example. It will always read either near 0V or near 5V depending on your active setting in Mach regardless of whether you're actually stepping or not i.e. it won't change.

Don't confuse a step signal with PWM - they're completely different beasts.

Offline Lubby

*
  •  25 25
    • View Profile
Re: Low voltage on 'step' pin
« Reply #4 on: March 04, 2015, 11:58:07 AM »
I've had the BOB powered by another source before using the charge pump but I'll check that again.

The BOB has a GND for the motor power supply but not the logic.  I know that having different power supplies that do not share GND can be an issue.  I have tried tying the GND of the logic supply with motor supply.  This didn't make a difference either. 

It's possible the issue is in here somewhere.  When running off the ardunio they all share the same power source.  Arduino and motor on a 8VDC supply.  BOB logic via the 5V output of the arduino?
It works fine with this.

I've been measuring with an digital ohm meter which I know isn't the right tool for measuring PWM.  That said, 50% pulse @ 5V reads at 2.5V;  20% High @ 1V, etc.  It's not perfect but it's what I have on hand and it does give some idea as to what's running through the wires.

What's the difference between PWM and Step Signal?  PWM = a specific pulse creating steps, Step Signal = as determined by PWM, G Code, or other source?

Offline Lubby

*
  •  25 25
    • View Profile
Re: Low voltage on 'step' pin
« Reply #5 on: March 04, 2015, 08:41:35 PM »
I've narrowed the issue down to the second parallel port.  Motor and driver work fine off original port.  I'll have to dig through the threads on second port again.
Thanks for the feedback.

 

Offline stirling

*
  • *
  •  2,188 2,188
  • UK
    • View Profile
    • www.razordance.co.uk
Re: Low voltage on 'step' pin
« Reply #6 on: March 05, 2015, 03:14:42 AM »
I've been measuring with an digital ohm meter which I know isn't the right tool for measuring PWM.  That said, 50% pulse @ 5V reads at 2.5V;  20% High @ 1V, etc.  It's not perfect but it's what I have on hand and it does give some idea as to what's running through the wires.

I suspect you're actually reading the output of the low pass filter fed by the PWM rather than the PWM itself. Imagine though, what your meter would say if you set your PWM at around 0.01% duty cycle?

What's the difference between PWM and Step Signal?

PWM is a signal of fixed frequency with a variable duty cycle. A step signal is a signal of fixed pulse width with a variable frequency. Almost the complete opposites of each other. Like I've said above, trying to measure the voltage of a step signal is like trying to measure the voltage of a PWM without the filter and with a vanishingly small duty cycle.

Anyway - the point is that you should not expect to see a changing voltage on a step signal with a multi-meter. That said it sounds like you're onto it with the 2nd port. Hopefully that'll sort things.
« Last Edit: March 05, 2015, 04:18:57 AM by stirling »

Offline Lubby

*
  •  25 25
    • View Profile
Re: Low voltage on 'step' pin
« Reply #7 on: March 06, 2015, 12:28:09 PM »
I'll have to read up on the PWM vs Step Signal.  Thanks for pointing that out.

I have all five motors working.  It was an problem with the voltage supply to the BOB.

Offline BR549

*
  •  6,902 6,902
    • View Profile
Re: Low voltage on 'step' pin
« Reply #8 on: March 08, 2015, 09:15:40 PM »
ON your second Port have you set it up AS input only OR both   In/OUT  . You may be triing to use an input pion as an output. AND you will get as you described.

(;-) TP