Use coolant control M7-M9 to start/end a job

My GRBL firmware supports enable coolant control (M7) and disable coolant control (M9). Instead of using that for coolant, I would like to use it to trigger the laser power and/or the ventilation. Basically it would mean that M7 has to be sent at the beginning of a job and M9 at the end.

Is that possible?

It’s possible, yes, but M8 and M9 are the ‘Air Assist’ functions for GRBL when using laser, so you would need to make sure all your layers had air assist enabled for it to work.

Aside from that, just change this in Edit > Device Settings to make it use M7 instead of M8:


Thanks for the quick response. Nice!

Is it also possible to use both M7 and M8 for a job? (Note that M9 will disable both).

Might seem like a strange request, but I could wire one relay to air suction, and one relay to the 12V of the laser (actually one will be wired to pin 5 of an LM2598 but let’s ignore these details…).

No, because there’s no way to turn one of them off without turning off the other one.

Ok, fair enough.

We recently implemented digital and analog output support in the Grbl_Esp32 firmware, which could be used as well. These do support independent on/off.

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