Limit switch - measure back emf

Hi. My 3d printed don't have any limit switches. It's using back emf to detect stalled stepper motor. Do you think it's possible to implement such homing procedure ?

1) start generating step signal
2) every 10-15 ms stop generating for a few us
3) read input pin to check back emf (0 - rotor is stalled)



  • This is something that needs to be added to firmware not host.

    emf needs also special speeds to work correctly and needs to be adjusted to motor, ... For TMC2130 a user has solved this for repetier-firmware and this driver, see recent thread in firmware section.
  • Sorry about that mistake. I was sure i'm writing on firmware forum.

    I will check mentioned thread. However i can't use TMC2130. My DRV8824 drivers are not replacable.
  • Don't think DRV8824 support stall detection at all. So that will not work.
  • It will work. It is working! I'm talking about Cetus 3D printer. What i want to do is to replace default controller (closed source) with repetier. There is one big board (power supply, drivers, relay, buttons, leds, ...) and small controller board (ARM cpu, wifi chip). Cetus team have updated regular switches to stall detection approach in mk2 version of Cetus 3D. They added some small chip (voltage comparator, i think) to detect back emf. And of course they updated firmware. It has to be possible to do the same thing in repetier.

    The is some alternative board:


    "IMPORTANT: FOR CETUS MK2 A downgrade to MK1 end stop is necessary, Please order the endstop from the below link"
  • Ok, if you add electronics to the chip you can do more that is clear, but the pure chip can't.

    Our firmware does not support smoothieware boards. They have a different processor then the supported one.
  • I know it's different board. It was just an example of board which sadly doesn't meet my requirement.

    Explain me please, why you think i can't use exactly the same approach as Cetus guys did? I'm going to try to modify reperier firmware. Unfortunatelly i have no experience with repetier code. 
  • I was not aware you wanted to make own electronics for emf detection. Sure if you want to spend many hours developing electronics and modifying firmware you can do. Easier solution would be I think to join TMC2130 conversation in parallel thread and use them on a RADDS board. Then you have the new hardware and a first implementation. And when V2 firmware comes out it will even improve support I think.
  • edited January 2018
    I'm going to make new CPU board (atmega2560) and to use existing emf detection. As as wrote before this is one chip solution (some operational amplifier in comparator configuration). All the magic is happening in cetus firmware. I have to modify repetier firmware to do the same thing.

    And i'm aware i could replace drv drivers or even everything. I simply don't want to do this. My goal is to change cpu board (as it's separate module) and nothing more.
  • Ok, good luck.
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