Fan speed sensing and monitoring



  • I am currently using a cheap Chinese 24V 30mm fan on my E3D for cooling. It started to make weird noise and I think it is going to fail soon.
    Is there a way to connect 3-wire fan to have fan speed monitoring on the Duet?
    If there is no direct way, then is there any simple circuit I can make to hook it up onto the Duet to trigger a macro so that I can stop the print and disable the hotend?


  • administrators

    RepRapFirmware supports a single tacho input. The fan RPM is displayed in DWC. For the Duet WiFi it should be connected to PB6 on the expansion connector. For the Duet 0.6 and 0.8.5 it should be connected to PA16 on the expansion connector.

    You won't get a good tacho reading if you PWM then fan, unless you use a 4-wire fan with a separate PWM input.



  • Sorry I am not very familiar with electronics and PWM.
    If I just want to know if the hotend fan is spinning or not, it a 3-wire fan enough?


  • administrators

    If it's an always on fan, or a fan you configure to run thermostatically, then yes. Connect a 1N4148 or similar diode between the fan tacho lead and the expansion connector pin, cathode to the fan lead.



  • I think you mean the cold end fan? Since that is always on at I assume full speed you dont really care about knowing the rpm. If its the part cooling fan then its going to be off for ABS. This is something I am going to do but put the rpm sensor via an arduino mega and output to an LCD since I have these lying around.

    As a slight aside you probably have a cheap fan which will have a sleeve bearing. Once the fan makes noise that is usually the sign the bearing is worn, especially if it does it on start up. What I do for "mission critical" fans is always buy dual ball bearing fans, these seem to last for years unlike the sleeve ones but they typically cost x5 as much.

    So the simplest solution is go buy a good quality dual ball bearing fan…..



  • Thanks David and gzcwnk for the info
    I will just buy a quality fan and leave the electronics behind then.


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