Ender 3 v2 with BLTouch intermittent failure



  • I am having the same intermittent issue with my OEM boxed Creality branded BLTouch kit, on my Ender 3 V2. It came with the five wire flat ribbon interconnect cable, and the BLTouch looks to be a genuine ANCLABS part. I am using the stock 4.2.2 system board, and the latest firmware as of 1/29/2021 from Creality's web site. This seems to be a fairly common problem, from other forums like Reddit. One part of why this problem has been so tough to track down could be that it is also influenced by the temperature of the BLTouch device. Thanks to the cold snap here, my ambient room temp dropped to 65F, and guess what, no more random failures after doing a dozen or so sequential bed level tests, with a cold bed and nozzle. Then I heated the bed to 90C, and the nozzle to 210C, and after an hour I repeated the tests, just after setting the bed and nozzle back to 0C. This time I now had the same random failures. Since I always do what is recommended by setting my bed temp to the temp I am printing at, which is usually 85C, before and during leveling, I think this is a contributing factor to the failures.

    Although this is certainly not excessively hot for the device, I know from my electronics engineering experience that semiconductor junctions decrease as temperature goes up, and thus become more voltage sensitive. So here is where I am going with this... I found a post where one person used a separate length of shielded sleving around the BLTouch cable, and it eliminated the intermittent issues. So I am thinking, that since it also fails when I disabled the nozzle and bed (after a warm up) that it is the X and Extruder stepper motors that are generating electrical noise, since even when not moving and parked, they are still pulsed by PWM to conserve power, and minimize heating. (I confirmed this with a current probe on a scope) I know it was previously mentioned that the cable was re-routed to eliminate interference, and it did not help, but unless great care was made to keep the cable way clear of the stepper motors, and that first section of cable sleving where it exits the controller, interference might still be induced into the BLTouch interface cable.

    Near as I can decipher from reading some threads on the Marlin site, is that this kind of problem can be caused what a fairly tight timing handshake does not happen from the BLTouch, or is interfered with after a probe Z touch is sent, and it expects an acknowledgement. Looks like Marlin has done great work on the code side, and it is outside of their control, when external stuff goes wrong.

    Here is a quote from the ANTCLABS BLTouch 3.1 technical pdf document;
    ※ If noise, etc. interference is expected, you should use an anti-interference extension cable (Shielded or Twisted Cable).

    With that in mind I ordered a twisted pair BLTouch interface cable to replace the stock flat ribbon one, and will give it a try and later report my findings. I will also do some more extensive probing and see what electrical noise levels are really present on the BLTouch lines. It could be that just the additional distributed capacitance of a twisted pair, or shielded sleving around the flat ribbon BLTouch interface cable is enough the dampen noise generated from someplace else, like the system board for instance, and it is not stepper motor driver/cabling induced like I theorized. Or it is something else entirely, and not interference. That is what I hope to test further and either confirm or eliminate as a cause. (Just have to find the time to tear it apart)



  • @admin OK thanks for the tip. I am afraid that I will just get on a rant with your support folks though, as to why ANTCLABS and the Creality BLTouch branded kit did not offer either a twisted pair or shielded cable solution from the beginning. And to take it one step further, a properly designed Differential signaling interface for noisy electrical environments, on both the part of ANTCLABS and Creality. This problem has caused me a lot of frustration, lost time, and damaged beds, and I see no reason to compound it by agonizing over convincing your support staff that it is indeed a real problem.

    Thanks.



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  • My apologies, I dorked this up with my original brain dead topic reply. New to the forum tools, sigh...

    I have replied to the OP, and this was resolved by replacing my OEM BLTouch flat ribbon control cable, with a twisted pair cable.


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