[obligatory note: I tried searching for PWM. "No hits." (really?)]
LinuxCNC v2.7, ubu 12.04LTS, generic 25-pin breakout board
I have a new Chinese CNC: 3-axis+rotary add-on. It came with a 15-pin proprietary card and NCStudio that won't install in Windows. ("Great! Motivation to 'do the right thing' at the outset.")
I bought one of those DB25-pin 5-axis breakout boards and (cannot hook it up because I have to wait on a gender-changer so my standard bi-dir cable will fit; however I) found another, very simplistic DB25-pin breakout that gives me easy access to the pins.
With that, in place, and assigning my pinouts in stepconf to match what the board expected (as best I could so far), I was able to verify with a DC voltmeter during "Tests" of the XYZ axes, that voltages appeared on the proper sets of pins which matched the expected movement commands.
Now, I'd like to do something similar for the Spindle pins: pin 1 which has been directed to provide "Spindle PWM" and pin 17 which has been directed to have "Spindle ON".
I notice that I cannot get LinuxCNC (the real version) off of Emerg. Stop (owing I think to its being unable to detect a machine hanging out on the parallel port), but I was able to use the Simulation version to get voltages on the stepper pins.
When I go into MDI mode and issue an M3 Snnnn, I would expect to read a steady voltage on pin 17 and a variable voltage on pin 1, but I don't see pin 17's voltage go off with an M5. Also pin 1's voltage doesn't seem to vary. (Of course, I'm not sure that the run through stepconf actually informed LinuxCNC to put the signals onto the pins requested.)
Of course there is the complicating factor of the signal being a steady amplitude, and only varying in pulse width, but I was thinking that my DC meter at least ought to read a different DC "average" as the pulse width varies. In any case, I expect it should read opposite extremes at M3 S0 and M3 S24000.
I'd like not to purchase an oscilloscope. Mostly because I know there's already one here. Somewhere. Under the flotsam.
If you can offer pointers, they would be appreciated.
Thank you for reading, and at least commiserating.
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Cnc Z'ne