Sorry Matd,
I just reread your post and see that you were already asking how to make the pwm signal. As I said in my earlier post, no hardware other than my bob is required (in my case anyway).
To make the pwm signal, in mach, setup the spindle to make the pwm and the z axis to turn it on and off (since I assume your laser machine doesn't have an actual spindle or z-axis). To do this, go to "ports and pins" on the "Spindle Setup" tab set the following in the Motor Control section: "Use spindle motor output" to on, "PWM Control" to on. "PWMBASE Freq to 4166 (I could use some help understanding this. I do know a lower freq seems to cause the power to be lower (I think)) "Minimum PWM" set to 0. In the "General Parameters" section set all delays to 0. In "Special Options" everything is off.
In the "Motor Outputs" tab, The spindle is set up as follows: Enalbed checked, step pin set to 16, the dir pin is 0 (we are not changing the direction of the spindle signal. remember we are using the Z-axis to do that.) Dir LowActive and Setp Low Active both unchecked. Step and dir ports both set to 1.
Also in the "Motor outputs" tab, set the Z-Axis as follows (all we are using is the direction signal). Enabled checked, step pin is 0, dir pin 1, dir lowactive checked, step lowactive unchecked, step and dir ports set to 1. ) I have to use pin 1 which is hardwired in my bob to control the relay on my bob.
Under Config>Spindle Pulleys, set the current pulley to number 1, min speed = 0, max speed 100, ratio 1, reversed off.
Of course, you can change the pins per your setup. In this case though, I have two wires going to the control terminals on my laser.... one from the common on my BOB, the other is hooked to the normally open side of the relay on my bob. The common side of the relay is hooked to pin 16 (the pwm signal). This way the relay can open and close the circuit which is sending the pwm to the laser.
Hope this helps,
Roger