second hand cnc from 2007,could use help with pwm on odd control board

I will read up on your post and see if I can get up to speed on your suggestion .im not real savvy with code or programming but I understand i need at least a basic knowledge of my own machine and the code I plan on running on it ,im slowly getting to that point.
would you mind me massaging you and asking your input as I come to any potential issues along the way. I appreciate your time and response so far as well many thanks.

I don't mind, but I think you'd be better served posting publicly where everyone can see your question.  No one person knows everything, and while I have a bit of experience with PMDX stuff & electrical hardware I'm far from expert on the workings of Linux and LinuxCNC.

[sorry in advance if this is too basic for you, mea culpa]
Specifically regarding your issue with PWM vs 0-10v....

A PWM signal  - regardless of voltage - is a digital on/off signal.  It's on, or it's off.  The computer (or controller) turns the signal on/off rapidly and the receiving device (VFD) interprets the ratio between on/off as a command.  i.e. 30% ON, 70% OFF = run at 30% speed (or however it's programmed).  Lcnc can turn one of your PMDX-122's output pins on/off rapidly to create a PWM signal.

The 0-10v analog signal is just that - the controller outputs a certain voltage, and the receiving device is programmed to run at a certain speed when that voltage is present.  0v = stop, 5v = 50% speed, 10v = 100% speed.

Your VFD (according to the manual snippets) can accept 0-10v for the frequency command (speed), or it can be pre-programmed for certain speeds when different inputs are triggered. Input #1 triggered = 10% speed, input #2 = 50% speed, etc.  Works, but not variable speed.

The problem you have is that the PMDX-122 has no analog output pin, and the VFD can't accept a PWM signal (which would be interpreted as a variable speed command).  Nor does your particular PMDX board accept an (optional) PWM-to-analog converter daughterboard sold by PMDX.

The only workaround I could think of was to use 'modbus' to communicate the speed command to the VFD.  Rather than providing a (likely poor) explanation of what modbus is, and how you can manage VFD's with it, you can read up on it in the LCNC user manual.

You'll likely have more questions - search the forum for "mb2hal" or "modbus" and try to digest as much as possible.

MB2HAL

thanks for the clarification. and no offense taken with the simplification of terms. and im pretty sure I understand the modbus concept buying an adapter to use two wire hookup to vfd from serial out, correct?

apparently ive not gotten a handle on even posting to the forum here because I was trying to respond to Andy Pugh about his solution and hence thats why I asked if I could message specifically if I had any hang ups in working that out.

honestly I'd probably be content to setup and use the 8 speed ability that this controller is suposed to have . once you factor in that I have 24000 max rpm. and likely would have a min practical usage of 5000/6000 for aluminum or if I was being ambitious maybe one day some steel for small guitar parts and use high quality bits with very small passes . thats likely something that I could just switch to manual potentiometer control for on the rare occasions I would attempt anything beyond wood and plastics aluminum anyway. without being long winded basically
I feel like I could have a minimum 8000, then 10,12,14,16,18,20,22,24. if im wrong and its only seven step well 10 -24 . 2000 rpm per step seems pretty functional for what its worth.

really its more that I'd like to learn how to do this and understand the machine I have than it is out of necessity. lol

i think maybe I can alway buy a 10$ pwm to 0-10v card off Amazon and have a fix but im keen on learning how all this stuff works and no better place to start than with an issue I already have in front of me. thanks so much for all the responses so far.

I am curious about one thing that maybe I've stumbled onto tho. it appears from what I've read that these 8 speeds or seven and an on/off are controlled by 4 inputs or an input to the board and accomplished through the 4 outputs to the vfd. when looking at the manual for the dsp in the setup is shows a grid with four columns running left to right with various boxes with either an up arrow or down arrow and for each speed there is a different combination of ups and downs .

am I correct to assume this is just the same four bits and depending on the combination you get a different speed or "gear change"

and if so is this an over simplified explanation of what Andy was trying to explain to me? how would I take advantage of this in linuxcnc if I wired things up to my vfd as in the second example on the manual page I posted. I hope im not bother this piss out of you guys with the noob questions. I stumble till it clicks then im usually pretty good from there on until the next learning curve presents itself.

After I wrote my response, I also considered a cheapo PWM to analog thing from Amazon.

Might be worth a shot, but it depends on how many stepper outputs you have available and are using.  If you have 4 outputs and are using 3, you have a spare that can be used as a PWM output (instead of a step & direction output).  If you're using all 4 motors and outputs, I don't think a general purpose output pin on the PMDX can be turned on/off fast enough for a useful PWM signal.  Somone smarter can correct me if I'm wrong.

Honestly, just set up three or four specific spindle speeds and get the thing working.  Once it's making chips see if you have the emotional fortitude to tackle some slightly more advanced LCNC configurations to get more granular spindle speed.

As you said, it's a router.  You aren't tapping steel at 500rpm. 95% of the time you'll set the speed to max and go to town.

beau wrote:

am I correct to assume this is just the same four bits and depending on the combination you get a different speed or "gear change"


 

Yep.

Have a look at MUX components in the LCNC manual.  Same concept.

linuxcnc.org/docs/devel/html/man/man9/mux4.9.html

thanks for pointing me towards mb2hal. and thanks to Andy as well. I think this is where I will begin and hopefully learn a little along the way in general. ive been reading other post about mb2hal since starting this thread. and the only other thing of any difficulty I can foresee that I will have to dive into is a ps3 or Xbox one controller I want to program to operate the machine with down the road so I am not either hovering over my estop on the machine / or tied to the keyboard away from the machine during programs. a longer leash would make me feel better.

im going to go through some basics and play around a bit more so I habe a little better understanding and not feel like im asking you guys to spoon feed me everything step by step . I feel like the fact that I can control stop/start through this old control board with nothing more than stepconfig wizard I cant be far off from working the multiple speed steps either so im gonna begin with wiring it as the multi step example shows and see if I can get the last three leds involved with speed control to blink as the first of the four does now for stop/start. ill then at least know im not far off and im in the right ballpark.

can someone explain the avi connection on the vfd ? most of the references ive found to vfd control have used this but they have been different vfds from mine.

beau wrote:

can someone explain the avi connection on the vfd ? most of the references ive found to vfd control have used this but they have been different vfds from mine.
 

I still get spoon-fed, not to worry.

AVI is analog voltage IN to the VFD for speed control.

The VFD is designed to use a potentiometer; it supplies 10vdc to the pot, and the pot outputs 0-10v based on the setting.  The 3rd pot connection is to the GND pin at the bottom (on the diagram).

Other VFD diagrams use "AI" and "AO" instead of "AVI" and "AVO"

As far as the ps2 or xbox thing... search for Feral Engineer on youtube.  He's got a superb walk-through of setting one up in LCNC.

I have extras for now tho not plentiful

1. unused
2. spindel on ( this is the only pin I can.
confirm has a physical connection to the.
spindel and speed portion of the bob.)
3. unused
4. x step
5. xdir
6.ystep
7. ydir
8. z step
9. zdir [×] inverted
14. unused
16. unused
17. chargepump


10.unused
11.x home ( all homes were shared.
home/min when running.
mach3 seems to make no.
difference in linuxcnc so I left.
them as only home.)
12.y home
13.z home
15. unused.
I think maybe I can put all homes on one pin if I really needed the extra spots but likely not.

im not entirely certain that all of the unused pins actually make their way to the control board from the pmdx though I have a strange very generic looking board between the pmdx and the control board .the parallel port from computer goes to pmdx , from pmdx physical wires leave the screw connectors of each pin and attach to screw connector on this "mystery " board labeled tigertec and a 50 pin cable connector is between it and the control board. I dont belive pins 2 ,14,15,16, (17 chargepump so no need to go anywhere ) are attached. I belive i can still make use of them but they arent going beyond the pmdx.

and this may be why I've not been able to switch around different pins on the port to light those other 3 leds on the control board ill have to investigate more.

anyway I appreciate everyone and their response and help so far ill attach a few more photos of what I have and I am open to any further advise/directions. I will try and take the leads I have gotten so far and try and make some progress with it this weekend. thanks again

some pics of weird board.