If you would like to fit both a spindle and a laser to your machine:

• Grbl only has one PWM output
• Easiest method to share this signal between multiple tools, it so add a Single Pole, Double Throw switch to direct the PWM signal between the two devices
• This can also act as a Laser Disarm switch, preventing the laser from firing (safety)

Wiring is as follows:

• PWM from BlackBox, to COMMON pin of switch
• PWM out from one side of the switch, to PWM IN on the Laser Module
• PWM (ON/OFF, as the IoT doesn't support PWM) to the control input on the IoT
• You can substitute the IoT Relay with Router for other PWM toolheads - the concept remains the same, the switch directs which tool sees the PWM signal from the BlackBox

Software / Firmware:

• Remember to disable/enable Laser Mode in Grbl Settings as applicable
• Learn more on https://github.com/gnea/grbl/wiki/Grbl-v1.1-Laser-Mode