3 or 4 wire hotend fan
I would like to put in a suggestion for future firmware.
With 3 and 4 wire 40mm fans getting cheaper, it would be a good idea to monitor and automatically control the fan. Say for example... A 3 wire fan is used to cool the hotend heatsink. The tach signal is being monitored by the Duet. Withing the configuration, a minimum speed value is set. If the fan speed ever gets below the configured speed value, a "pause" macro could be initiated, then if the fan speed still does not recover, a "stop" macro could be initiated.
That way, if the fan ever stops, the printer would notice the hotend is no longer being cooled, and it could protect the printer from a meltdown.
This idea also could be carried over to other cooling needs, like cooling the Duet board it's self. If the fan ever stops, the Duet would notice it, and run a macro that could inturn stop the print.
RRF on Duets already supports a single 4-wire fan. See https://duet3d.dozuki.com/Wiki/Connecting_and_configuring_fans#Section_Connecting_4_wire_fans. The prototype Duet 3 main board includes three connectors for 4-wire fans.
Using the tacho output of a 3-wire fan is problematic if PWM is used.
@dc42 that is great the Duet can control a 3 or 4 wire fan, but what about running a macro when the fan speed is below a set point (or no speed at all), can the current Duet do that now?
@dc42 that is only what I was suggesting. Thank you for the work you do.