@martin1454 said in Gcode macro - Get parameter (fan rpm):

Is there any way to get what the current "fan speed" is for an output...

Yes, send M106 with just a P parameter to specify the fan,

...and use that value to subtract 25 and write to m106?

Not yet.

@pro3d said in Will 12v fan on 24Vin blow up the board?:

@dc42
Thanks for the response! Not many radial 4020 blowers on 24v

But can connecting wrong fan to one port destroy all of the FAN outs?

Shorting one fan output can damage a trace on older Duets, or blow the 1A fuse on revision 1.03 Duets. But in that case, the fans won't run at all.

Followup question
I also connected the bl touch before making it 3.3v ready --- Are more components now dead?

Unlikely. We can't guarantee it, but the endstop and Z probe inputs will generally tolerate a lot of over-voltage without damage.

The heatsink fans supplied by E3D do not work with PWM, so you will have to be content with turning them on and off.