MUXing external stepper drivers



  • Hello,
    Can i MUX the En,Step and Dir pins for the external stepper driver ? I guess the breakout boards for stepper drivers would just share the operating 3.3v & GND and wouldn’t be muxed.
    I know i have to disable idle current prior to switching...
    I would like to do it with analog multiplexer and utilize the unused 100-103 GPIO pins on the Duex5 board for multiplexer control.

    I would need only one (13.th) stepper motor, but since 4 GPIO pins can multiplex 16 channels, this might just open new possibilities for me 😉


  • administrators

    In theory, yes if you only need to drive one of the multiplexed motors at a time. You would need to multiplex both the STEP and DIR pins, and keep the drivers permanently enabled. You would need to modify the firmware to set the multiplexer before generating the step pulse.



  • @dc42 yes, it’s one at a time scenario. For extruders.
    Ok, so only step and dir, ok. Even better

    Edit the firmware to send signal through GPIO?

    I thought of just adding muxing sequence in toolchange scripts...
    Like

    M84 E4
    Dwell for like 500 ms
    M42 P100 S1
    M42 P101 S0
    M42 P102 S0
    M42 P103 S0

    So this is not enough?
    What would i need to change in firmware if that’s not ok?



  • with a bit of luck you might get away with an i2c based multiplexer and sending the commands straight from tool change macros?


  • administrators

    @MaracMB said in MUXing external stepper drivers:

    I thought of just adding muxing sequence in toolchange scripts...
    Like
    M84 E4
    Dwell for like 500 ms
    M42 P100 S1
    M42 P101 S0
    M42 P102 S0
    M42 P103 S0
    So this is not enough?
    What would i need to change in firmware if that’s not ok?

    Yes, I think that would be sufficient, in which case no firmware changes would be needed.

    You would not need to turn the drivers off using M84 if you kept them all enabled. Or if you prefer, you could multiplex the Enable line as well, and use pullup resistors to disable the non-selected drivers. It depends on whether you want the non-selected drivers to be enabled or disabled.

    Also, you would not need to multiplex the DIR line. So a single 74HC238 chip to route the step signal may be all you need.



  • @dc42 thank you



  • @bearer exactly.

    Duet3D, the best thing that happened to RepRap.


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