Duex4 and Servos / BL-Touch

  • Hi Folks,

    I have a Duet 0.8.5 with the Duex4 expansion board and I am wanting to connect a BL-Touch. From what I can see the usual way is to use one of the heater channels as a servo output by connecting to the expansion connector on the Duet. However, that connector is in use in order to connect the Duex4. A quick look at the schematics shows that the heater outputs on the Duex4 switch between VIN and GND which would let all the magic smoke out of the BL-Touch.

    So my question is this - Which of the following possible solutions would work best:

    • Intercept the signal in the ribbon connector, leaving the input on the Duex4 floating

    • Solder the PWM signal cable for the Bl Touch to the relevant pin on the bottom on the Duex4

    • Add a level shifter to the appropriate H- pin

    • Non of the above (Suggest an alternative please)

    Alternatively, is it possible to output a PWM signal on the PC4_PWML1 pin on the Duex4 expansion port (physical pin 10, Logical pin 69)? If so I could add some additional electronics (arduino, perhaps) to convert this signal into a valid servo signal.



  • administrators

    The DueX4 expansion pins that are available are listed at https://duet3d.com/wiki/Using_servos_and_controlling_unused_I/O_pins. What I can't remember is which ones (if any) are servo-capable. Any that are could drive the bltouch directly because it seems to be happy with a 3.3V signal.

    Other than that, all of your suggestions sound suitable. For a level shifter, a small signal diode and pullup resistor to +5V would probably be sufficient.


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