On your BOB, which pin outputs a PWM signal?

Yes, you can use any two of the output terminals of the breakout board to control the SuperPID closed loop router controller (a diagram is not needed with these instructions). One output terminal will be used as an on/off (1/0 or 5v/gnd) that will be invoked with the M3/M4/M5 M-codes in your g-code instructions. The other terminal will be connected to either another 5v/gnd signal to control speed for 5000/20000 rpm or for PWM output (recommended) for proportional speed control. To setup this configuration in Mach3, go to your ports and pins dialog box (config menu -> ports and pins). Click on the spindle setup tab. In the Motor Control Section of the dialog, check the box for Use Spindle Motor Output and check the box for PWM control. Change the PWM Base Frequency to 50Hz.