UNSOLVED BL Touch Self Test Speratic



  • On power up I see that some times the BL touch will run a self test and other times it will not. When it does not self test it will not extend during the Z home. If I power cycle the printer once or twice the BL touch will then self test and work properly.

    Is it possible that there is a background command being issued at startup that may be preventing the self test?

    Is it possible to add logic to the home routine to check that the pin is extended? I know that the trip value P is set in the G31 command, is it all possible to interigate the P value manually? My thought process is to extend the probe, wait some time, then check that P is equal to some value, if not error.



  • Hi,

    Did you try adjusting the grub screw at the top of the unit?

    Check the docs for how this is done.

    Frederick



  • I'll give their manual another read. I thought that set screw just adjusted sensitivity.

    It still would be nice to have positive feedback on the extend with it being so critical for homing.



  • Hi,

    I mentioned the grub screw because that is the only adjustment that you can make - it may or may not help but what else can you do.

    Did you add an "Alarm Release" command to your config.g file?

    Frederick


  • Moderator

    It could be a loose wire connection or failing probe. Having a spare probe to test against isn't a bad idea.



  • I replaced the BL touch unit and I still this. I've also seen this on separate printers. And I've quadrupedal checked the wiring. If i power cycle 2-3 times the self test will run and everything works fine. If I then power cycle again the unit will not do anything and no commands will work. If then disconnect and reconnect the two power pins the self test will perform.

    Looking at the BLT timing diagram I see that there is a minimum 100ms delay before setting PWM so an internal power check can be run. I'm running using a 24 V power supply for the duet and a seperate 5V power supply for the duet logic. Is it possible that there is some power delay on the 24V or 5V side of the board which is cutting into that 100ms wait time.



  • I disconnected the PWM cables and powered the BL touch direct from my 5V power supply. I still see the same results of the self test only occasionally being performed on power up. Looks like it is an issue on the power side.



  • Did this ever get sorted out? I am having issues with my BLTouch not deploying off my Duet3/Toolboard setup.
    My BLTouch clone self tested fine, updated to a Genuine BLTouch v3.1 and now no self test...



  • @I_Jedi

    I found that the 5V signal to the BL touch was not instance on, but instead "slowly" ramping up to 5V. The BL touch was not seeing 5V fast enough and going in to error. I added a time relay to create a slight delay before powering the bl touch and it remedied my situation.



  • @Eduma Thanks - a time relay is not realistic on the Toolboard, so I'll just have to run with it 🙂 Appreciate you sharing your solution though!



  • @I_Jedi said in BL Touch Self Test Speratic:

    @Eduma Thanks - a time relay is not realistic on the Toolboard, so I'll just have to run with it 🙂 Appreciate you sharing your solution though!

    There is a servo position you can send to the BLTouch to force the self-test.

    Frederick



  • @fcwilt Thank you... the question at hand is should the BLTouch automatically do an unprompted self test as soon as it has power. Several of us are having an issues with the v3.1 on the Toolboard. There is a suspicision that it is not getting sufficent 5V immediately during boot up to run test. So fallback appears to force a M280 P0 S120 in the startup gCode



  • @I_Jedi said in BL Touch Self Test Speratic:

    @fcwilt Thank you... the question at hand is should the BLTouch automatically do an unprompted self test as soon as it has power. Several of us are having an issues with the v3.1 on the Toolboard. There is a suspicision that it is not getting sufficent 5V immediately during boot up to run test. So fallback appears to force a M280 P0 S120 in the startup gCode

    Well put. I have confirmed the same behavior with the toolboard.



  • I am also still investigating why the BL Touch goes into an alarm state (blinks red) so often when connected to the toolboard even though everything appears to work fine and it responds to all commands..



  • @oozeBot I am not quite that far... still finishing first time start up... That is quite frustrating. I hope we get someone from Duet to let us know what to try/look for/patch firmware...



  • Hi,

    I would imagine the probe is not seeing the power conditions that it expects to see on power up and is behaving oddly.

    I would use the "reset" and/or "self test" commands as needed.

    Frederick



  • @fcwilt said in BL Touch Self Test Speratic:

    Hi,

    I would imagine the probe is not seeing the power conditions that it expects to see on power up and is behaving oddly.

    I would use the "reset" and/or "self test" commands as needed.

    Frederick

    This does not appear to be a reliable fix. In fact, M280 P0 S160 doesn't even clear the red flashing state most of the time. I'm ignoring it for the moment but really want Duet to weigh in..



  • @oozeBot

    Hi,

    Is this a clone or the real thing?

    Frederick



  • @fcwilt the real thing - v3.1. In fact, I purchased two more this past week and both are exhibiting the same behavior when connected to the toolboard.



  • @oozeBot said in BL Touch Self Test Speratic:

    @fcwilt the real thing - v3.1. In fact, I purchased two more this past week and both are exhibiting the same behavior when connected to the toolboard.

    Sounds like some compatibility issue between the toolboard and the BL.

    Now this doesn't address the problem BUT I've recently replaced my BLTouch v3 units with 12 mm inductive sensors. They take a little bit more space but the results are better than I ever got with the BL units. And they don't click.

    Frederick


  • Moderator

    @oozeBot @I_Jedi

    @dc42 runs a BLTouch on a toolboard in his setup, and as far as I know hasn't had these problems. How are your electronics set up? Is the Duet powering a RPi, with peripherals (eg screen)? Any other boards or sources of power drain/interruption on the 5V power? Can you put a scope on the 5V at the tool board, and see if the voltage is being pulled down?

    @dc42 also suggests: "It would be helpful if some one could test whether putting additional capacitance e.g. 100uF between +5V and GND solves it."

    Ian



  • Here is a picture of my electronics.. using a350w Meanwell power supply, Duet 3, RPI4, tool distribution board, and the toolboard is mounted to the tool head.

    Unfortunately, I don't have access to a scope, nor do I have any 100uf capacitors, but can order some if there is a strong desire to learn if this corrects the issue.

    electronics.jpg

    printhead2.jpg



  • @fcwilt @I_Jedi @oozeBot

    I had found that after machine power up the bl touch would immediately run its self test and begin to flash. If I disconnected power to the bl touch then reconnect it would run its self test and complete the test without issue. This worked 100% of the time. This lead me to connect a scope my cheap 24v to 5V power converter and found that the 5V was a gradual increase instead of an instant on.

    I tried utilizing the reset command but did not have consistent luck. I believe that reset is only intended for probe up/down failures, not power alarms. Would be great if BL touch offered an up/down/error outputs. Would also be nice if you could actual see the blue indicator light.



  • Got a new battery for my multimeter and confirmed it's reading right at 5v. I powered down, plugged back in after 10 seconds, and it immediately read 5v. There is nothing else connected to the toolboard's 5v rail.

    As stated, it has never done a self-test at startup. After rebooting, it glows steady red (with the occasional blink). M401 works. M402 works but the probe immediately begins flashing red. It is doing this on two brand new BL Touch v3.1 probes.

    Again, it is working even in this error state of flashing red, but something is still obviously wrong. At this point, I'd love someone to call me out on some glaring error I should have caught, but I don't know what else could be wrong. The relevant lines are below. Toolboard is on B20. I've tried both with and without the ^ with the same results.

    M950 S0 C"20.io0.out"
    M558 K0 P9 C"^20.io0.in" H5 F120 T10000 A5 R0.1 S0.01



  • @droftarts Thanks for sharing the word from the experts -- I have an extra 120uF from grounding the second twisted pair in the ADSL line. I dont know enough about resisters to know if that is close enough value, but will give it a go. Does direction of the resister matter? For what its worth, I am powering rPI and a 7" screen off of the Duet3 board.


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