Using PDM mode for Spindle Control

Hello,

I have a Sound Logic Combo Board, it does the break out and spindle speed control.






It uses a circuit that converts 0 to 20,000 Hz to 0-10Vdc .

I need to configure Linuxcnc to produce 0 to 20,000hz on pin 1 which I have configured in StepConf to be PWM and have set it to PDM mode ( photos attached.) Im not sure if this is the correct step.







I have had some limited results, I can change the settings for RPM span in the Spindle Config menu but it only ever gives me a range of 0- 4.18VDC on my board, this leads me to think that linuxcnc is not putting out a 0-20,000Hz frequency. Im guessing I have to change the HAL but I have no where to start. Any help is greatly appreciated.

Noah

Hallo Noah,

you have not entered a PWM Rate, so it is using PDM.

I Do not know if you can enter 20.000 for the PWM Value, on one of my controls I used 100 Hz.

The spindle values represents a rpm value and a % value of the output.

Norbert

Norbert,


I am using PDM on purpose. My understanding..(correct me if I am wrong) is that PWM is a given frequency (e.g. 100Hz) and the duty cycle is modulated. In PDM mode, it is changing the frequency. This is my understanding.

I would lke to use the change in frequency. 0- 20,000Hz. to represent 0-20,000RPM which my board converts to 0-10VDC.

Noah

For a spindle 0 to 10V interface that uses frequency instead of pulse duty cycle to set the output voltage
neither PWM or PDM are appropriate.

You will need to either use the siggen component or a stepgen running in velocity mode to generate
the variable frequency.

I dont think stepconf knows how to do this so this needs to be done by editing your hal file

Ok! Thank you!

That's what I was dreading but I guess that means I get to learn more!

Noah