Driving a Relay through extruder stepper output



  • Hi everybody

    I need to drive a ON/OFF relay through a extruder stepper output.

    The idea is to activate relay when extruder is supposed to extrude, and to Switch OFF relay when extruder is supposed to retract or stopped.

    How could I managed this ?

    Duet2 Ethernet + Duetx5 / RFF3

    Thanks !



  • @sylvain do you need to use the actual stepper driver output or just have it correlate to any movement on the E axis? And is it instead of a regular stepper motor, or in addition to the stepper motor.

    As far as I can wrap my head around it, neither will work without hacking the firmware, but clarifying the above might help get some relevant pointers on where to go hacking.

    edit: simplest approach may be to use an external stepper driver on the CON_LCD and a little bit of external circuitry to buffer and stretch the step pulse so it would hold the relay closed while there is a continuous stream of step pulses. (or tap into the step signal for an existing driver if you need both)



  • I do not need a stepper motor to run in the same time.

    The idea is that slicer generates E movment and that these E movment activates the relay.

    Thanks !



  • Then the CONN_LCD header will allow two adittional stepper drivers to be attached, the firmware will generate step pulses in relation to the E movement.

    Then you're left with smoothing the pulses so you get a continuous signal when extruding, this could perhaps be as simple as a diode and a capacitor, maybe a resistor to tune the time constant, and an external relay moduel with a built in transistor to drive the coil.



  • What is your usage case?
    If you're not FDM printing, but instead trying to control an external device via the relay (like say a welder), you could probably set the machine up in laser mode.
    See M542
    https://duet3d.dozuki.com/Wiki/Gcode#Section_M452_Select_Laser_Printer_Mode


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