[rschwarz]

Hi ,
I have a manual milling machine (PM25) that I recently converted to CNC.
I would like to controll the Spindle from the PC instead of manually with the speed control Potentiometer on the mills controll box.

I would like to use the existing spindle control board that came with the manual mill.
I was thinking of replacing the potentiometer that controlls the spindle speed with the analog output of my breakout board(0-5V).
(I verified that the manual potentiometer signal is between 0-5v)

However I am worried about connecting the Ground from my breakout board to the ground of the Spindle control board.
It seems to me that both grounds do not necessarily have the same potential.

My Question:
What is the best way to replace a potentiometer with a PWM controlled analog output (without the ground issue)?
Can anyone recoomend a PWM board that is optically isolated?

My breakout board is : the chines ST-v2 board (see attached pictureAttachment 395722)
My Spindle controll board is: spindle control board that ships with the PM25 milling machine

[john-100]

which speed control board is used in your PM25 ??

if its like the PWM controls like FC250J/230V
Attachment 395742
found in old Clarke CL300M mini lathes or XMT2035 in later versions

or KBIC -240D from KB Electronics is found in the Warco WM180 lathe
Attachment 395744

Don't connect them to your Breakout board !!!


both types of board using either FET's for PWM control or Thyristors as part of a controlled bridge rectifier

have the speed control potentiometer connected to the live PCB board !!!!
and must not be connected to your breakout board


John


your break out board limit switch / E stop ground is connected to the analogue 0-5V ground which is also the 24V supply 0V connection !!!!

Attachment 395754