pwm schematic help required please?

[Doddy]

The issue here is that the OP's spindle speed control looks to be a digital PWM input drive, not an analogue input voltage. I accept this is somewhat different to the standard option on many speed-controllers on a standard spindle inverter driver.

In using the BOB the OP has inadvertently adapted the PWM output from the PC to an analogue voltage.

The Speed Controller looks to use only a PWM input.

The easiest test now would be to try to source the PWM output from the PC (looks to be available on pin 'P1' output on most BOBs), and feed this to the pin-3 of the speed controller. Connect BOB ground to pin 4. If this works at all - if the speed range is inverted (low = high speed, high = low speed) then write to confirm.

Or, if the PWM output from the PC (into the PWM input on the BOB) then look to remap via Pins/Ports from Mach to a different output than '1', and try again.

The original Pot set-up looks (a) to be mis-wired, and (b) likely intended to be a potential divider to scale input - whether this was PWM or analogue to a lower voltage/current. If the value of R5 is 4k7 then this just isn't needed for the opto-isolated input for any supply up to 10V (If ~= 4mA on the opto-isolator LED at 10V input). BUT, unless you get a PWM signal into it I doubt from the quick look at the board that this will give anything other than On/Off. The OP needs a PWM source.

EDIT:

OP: On the image of your BOB - what's the label on the fourth pin from the left on the top edge of the board (after the Red/Red/Yellow cables)? - Is that P1?