CNC spindle speed feedback with control via fan headers

[CNCModeller]

Hi all,
Starting to seriously look at a retrofit of my CNC mill to duet.

A while ago there was discussion on using a pwm fan header for speed control and using fan speed feedback to monitor spindle speed.

Is this viable, and if so could this be used to close loop control the spindle rpm?

I've got a pwm to 0-10v conversion board to signal the original spindle drive card but it's open loop, i.e. it doesn't have speed feedback.

Is this something that would work in CNC mode?

Any constructive thoughts would be great.

All the best
Barry M

[o_lampe]

@cncmodeller That's probably a better aproach then the heater/thermistor idea in the other thread, but it would require FW adaption.
A spindle definition would then be a combination of Fan.rpm reading and heater PID algorhythm.