Resistor needed for probe on 1.04 boards?



  • getting ready to install the BLTouch on my Duet wifi 1.04 board. I think both the board and the BLT are the most recent version. A friend tells me that I don't need the 240 ohm resister on the newest Duet and BLTouch. Is he right?

    Also, if I do need it, then this resister would go between the probe pins 1 and 2 on the Duet board, correct?



  • If it's the newest BLtouch it wouldn't come with a resistor, it would have a trace on the probe that can be cut to enable 3.3v logic.

    The Duet would work with it without the resistor, or even the trace cut, but there are so many versions and clones that it's hard to really say. Some people have had success without, some have said that adding the resistor or cutting the trace made it work.

    Check this out: https://duet3d.dozuki.com/Wiki/Connecting_a_Z_probe#Section_BLTouch

    For all Duet 2 WiFi/Ethernet boards prior to version 1.04
    If you have the older BLTouch, also connect the 240 ohm resistor between Probe GND and Probe IN. On the newer BLTouch, cut the PCB trace on the BLTouch to reduce the output to 3.3V as described in the BLTouch instructions.

    The Z probe input on the Duet 2 Maestro and Duet 2 WiFi/Ethernet rev 1.04 and later is 30V tolerant, so it doesn't matter whether you reduce the output of the BLTouch to 3.3V or leave it at 5V.


  • administrators

    You do not need to cut the trace or use the resistor when you connect it to a revision 1.04 Duet WiFi/Ethernet or a Duet Maestro.



  • Great. Thank you. I cut the trace before submitting this question, but glad I don’t have to fuss with the resistor.


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