With PWM lasers being used more widely on CNC's in conjunction with the CNC Shield Controller Boards running Grbl 1.1+ the question of how to wire the laser and the Z limit switches seems to be popping up more and more.
Well, Here's a diagram that shows the answer as simply as possible.
It all stems back to prior grbl versions where PWM was not common for laser modules, instead they were wired into the spindle enable port and keyed on and off, with no Pulse Width Modulation (PWM). Grbl was updated to include PWM and the existing boards could take advantage of this update, but there was one small caveot, the pin that was needed to access the chip on the arduino board capable of PWM output was already being use. It was being used for Z limit switch. the simple fix for this on grbl included swapping Spin Enable, which is not capable of PWM, with Z+ limit switch pin.
A rather simple change, but a bit confusing to users of now mis-labeled cnc controller boards.
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