No BlTouch readings



  • Hello,

    I have set up my Bl Touch like descriped in the wiki. So far everything works fine. I can manually deploy and retract the probe and if I click on Home Z (in the Web Interface) the Probe deploys and bed is moving up. So far perfect. But the probe does not trigger. I want to use it as probe and as Z endstop. I think it is something with the configuration. Because I am extremly new to Duet I am not so familliar with it (used smoothie bevore and bltouch worked).

    config.g
    ; Endstops
    M574 S0 ; Define active low and unused microswitches
    M574 X1 Y1 Z1 S1 ; Define active high microswitches
    M558 P5 X0 Y0 Z1 H3 F120 T6000 ; Set Z probe type to unmodulated, the axes for which it is used and the probe + travel speeds
    G31 P50 X0 Y-64 Z1.15 ; Set Z probe trigger value, offset and trigger height
    M557 X15:290 Y15:318 S20 ; Define mesh grid
    M307 H3 A-1 C-1 D-1 ;

    bed.g
    ; Clear any bed transform
    M561

    ; Deploy the mechanical Z probe
    M98 Pdeployprobe.g

    ; Probe the bed at 4 points
    G30 P0 X15 Y15 H0 Z-99999
    G30 P1 X15 Y318 H0 Z-99999
    G30 P2 X300 Y318 H0 Z-99999
    G30 P3 X300 Y15 H0 Z-99999 S
    ; Retract the mechanical Z probe
    M98 Pretractprobe.g

    homez.g
    ; Lift Z relatively to current position
    G91
    G1 Z5 F6000

    ; Back to absolute positioning
    G90

    ; Go to first bed probe point and home the Z axis
    G1 X15 Y79 F6000
    M98 Pdeployprobe.g ; Lower Z probe BLTouch
    G30
    M98 Pretractprobe.g ; Retract Probe

    ; Uncomment the following lines to lift Z after probing
    ;G91
    ;G1 Z5 F100
    ;G90

    Would be very nice if someone could help me 🙂


  • administrators

    That configuration file looks correct to me, assuming that you have connected the probe output correctly to the Z probe connector, Can you post a photo showing that connection?

    When you have deployed the probe, what Z probe reading does the web interface show, both when you push the probe up and when you don't?



  • This is the wiring.

    The webinterface reads always 0. Except when pull the probe connector (black and white cable from Bl, GND and signal). And with M119 it tells me that: Z: at min stop, Z probe: not stopped
    Maybe this helps. I have also conntacted Antclabs because after some more investigation this night I found out that there is no voltage between GND and Signal out. Even when it is in alarm mode. I did read it should send a continous signal when in alarm mode. Maybe some one who has a defenetly working Bl touch could also test this



  • In my experience witht eh BLtouch, the web interface rarely responds fast enough for the probes super fast pulse, to get it to register occasionally i would have to deploy the probe, and then manually press the pin multiple times to get it to register once. Also, unlike a mechanical switch, 2-wire output for the touch seems to be polarity sensitive. On both my Rambo boards and the duet, polarity has mattered.



  • I already checked polarity and wiring a few times…
    What happens with the output of your Bltouch when it is in Alarm mode? I did read that it then has continuos Signal output so we should be able to measure some kind of voltage.
    I also checked it with pushing the pin like 300 times up und the webinterface didn´t react once...
    I only get a reading if I disconnect the output wires


  • administrators

    It does sound as though your sensor is not producing any output on the signal wire.



  • Right now I am setting the Touch up with the old board to see if it still works.
    But the config is right yes? Becaus it says : "Z: at min stop, Z probe: not stopped"
    And one more thing because I didn´t find something about this. Were do I need to home when I home with the probe? From Smoothie I am used to home at the first probe point.
    And will the IR sensor be in stock soon? Might wanna try it out


  • administrators

    Is the IR sensor out of stock at duet3d.com? I wasn't aware of that. You can still order it from me direct at escher3d.com.

    If you are using a Z probe to do Z homing, I suggest you do it at the centre of the bed.



  • As a way to test the output of the probe



  • Finaly I got it working.
    I took the Touch unter the microscope to see if there is anything with the solder connections. And there it was. A little part of the Signal wire did a short to the GND wire next to it (really no human could have seen this with his eyes). Seems like a bad soldering job. So signal pin always was pulled down to GND. Its working fine now. Thanks for the help guys 🙂
    Setting up now all the rest. How do I need to name the mesh leveling macro for G29?


  • administrators

    Unless your printer is a delta, the simplest approach is to put your gcode to deploy the probe, run G29 and retract the probe in file bed.g. Then you can use G32 or the Auto Bed Comp button to execute it.



  • @dc42:

    Unless your printer is a delta, the simplest approach is to put your gcode to deploy the probe, run G29 and retract the probe in file bed.g. Then you can use G32 or the Auto Bed Comp button to execute it.

    Just for clarification, as I've been fighting with configuring a cartesian printer using a bltouch, is the G29 going to negate the need for the z-home, or is there a simple routine to use the bltouch (or any z-probe) for z-home probing as well?


  • administrators

    You need to home the printer completely before you run G29, but you can use the Z probe to z-home. See https://duet3d.com/wiki/Configuring_RepRapFirmware_for_a_Cartesian_printer#Homing_Z_using_a_Z_probe for details, but add M401 and M402 commands around the G30 command to deploy and retract your probe.



  • Thank you, FlowerBob and DC42. This thread helped me get my printer zeroing and bed probing after digging through the wiki I don't know how many times, only to end up off in the weeds trying to figure out what I was doing wrong.

    Now, if I can only figure out how to prevent my bed sagging so far due to the overly thin material provided by the kit maker…


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