Precision Piezo sensitivity on Duet Ethernet 2

  • Hi Everyone!
    I have been using a BLTouch on my Folgertech FT-5 R2 for awhile now, and I have recently upgraded to a precision piezo universal kit. The piezo is mounted behind the extruder's stepper motor on precision piezo's NEMA 17 mount.
    I am running into issues when I go to do a probing move (either issuing G30, or running mesh bed grid compensation). When the nozzle is pressed up (my finger barely touches the bottom of the cold nozzle) the red light on the amplifier board goes off, and the blue light lights up (blue stays lit for about .25 seconds, then goes off), then the red light comes back on. I have both VR1 and VR2 set as high as they can go without constantly triggering.
    The trouble is that DWC doesn't register a change (either in analogue or digital mode) until I press up on the nozzle. Hard. (Enough to cause the bed stepper motor to loose steps when moving.) The piezo is connected to the amplifier by wires that are no longer than 100mm.
    Any help you all could offer would be greatly appreciated!

    Duet Ethernet with RRF 2.03 beta 3.
    Precision Piezo Universal 2.85 with 20mm piezo
    E3D Titan Aqua with Volcano Block

    Config.g Section:
    M558 P1 I1 R0.2 F300 X0 Y0 Z0
    G31 X0 Y0 Z-0.1 P300
    M557 X20:275 Y20:275 S50

  • When the red light goes off the Precision Piezo digital signal has triggered. I sounds like the duet is not seeing the signal correctly. I would recommend:

    1. use the digital signal
    2. use the z-probe connector
    3. M558 P8 H3 I1 F300

    You will need to play with the sensitivity to prevent premature triggering during the probe dive.

  • I have the Orion so this may not exactly apply but when you're in analog mode, the adjustment pot only controls the LEDs not the actual signal. Since you seem to have that adjusted correctly based on your "finger touch" test, I'd do as @tj suggests and try digital mode first using P8 as the probe type.

  • if you switch to RRF3 there's a trick I'm using

    before you run any probing you reconfigure treshold:

    G31 P{sensors.probes[0].value[0] + 5}

    it reads current value and sets treshold to +5

    works like a charm (you might want to use +10 depending on what type of interference you have on orion)

  • Thank you all for replying! Okay, so I finally had some time to take a look at it today.
    Unfortunately, the piezo is still requiring about the same amount of high force to trigger the Duet (while in digital mode).
    I am starting to think that there may be an issue with the way that the hotend/extruder is connected to the piezo mount. When I insert the piezo into the mount, it feels like the solder joints are pressing out on the mount, making the hotend assembly have to use even more force to bend/press the piezo. Could this be the case?
    On a somewhat different note, what is the typical resistance or voltage either across VR1 and VR2, or from VR1 or VR2 to ground? (I want to make sure that the pots are set correctly.)

    Thanks again for all of your help!

  • @tbluml orion doesn't have 2 pots, only one, and that one failed me on the first day so I moved to analog output. The old PCB doesn't have an analog output so not helpful 😞

    I have old version on another printer (not duet powered) and there I have:
    VR1 (1M)
    Probe- 173k5 - VIPER - 0M8537 free leg

    VR2 should be 100k but mine measures 16k36 as you have R12 and R11 in parallel. Measuring VR2 I read this:
    vdd - 28k5 - VIPER - 27k gnd

    These are in-circuit measured values so as there are other resistors in parallel results are not showing exact resistance value of the pot itself


    There is, unfortunately, no schematic available for the Orion and its analog output (I asked they are not sharing 😞 ) but if I understand correctly you are using this old version anyhow so this might help you out.

    With regards your comment about mounting:

    • yes, make sure you put the disk in a way that solder joints are "free". If required dig a channel in the holder so that solder joints don't get any force applied on them, not only that the system will work with less precision, bigger issue is that miniature force applied to those solder joints and they will just break off the disk as they are hanging on a super-thin metalized layer on the ceramic, look at them wrong and they just drop off.
    • I had some serious issues with the piezo sensors in the past but after I got them to work they work for years without any tweaking, fixing... they just work. I recently ordered Orion (should be lot better than this old system) and again I had a lot of issues setting it up, guys from PP were very helpful so I made it work using analog output (I think something died on that board as it's not working the way it used to with regards to digital output, also the single pot this one comes with died the first day so if you ever go with Orion just ignore the pot and use the analog output as that pot just craps out after 5-6 turns).

    Things that helped me so far (I have 3 printers using PP ATTM):

    • tightening the screws pressing two parts around sensor disk
    • loosening the screws pressing two parts around sensor disk
    • 2sec " recovery time" for probing M558 P1 C"" R2 H5 F1200 T3000 A3 S0.03 K0 the R2 part here. This way before any Z probe the system will stay still for 2 seconds allowing any triggering happening during the XY move to settle down
    • higher probing speed - F1200 in the config telling the system to probe using 20mm/sec. In my setup, if the bed approaches the nozzle slower than 20mm/sec it will not produce enough voltage from the sensor to trigger. 20mm/sec is triggering sensor properly every time
    • set JERK for Z to zero M566 Z0 according to documentation and discussion here on the forum this should not have an effect but guys from PP told me to put it, I did and it started working better so I'm keeping it. I'm only setting jerk to 0 during probing, I set it back to regular value for the printing.

    Yes, you read correctly, sometimes having PP contraption tighter worked better, sometimes having it looser worked better, you have to experiment.

  • @arhi Thank you! I will take a look at that. I apologize if I didn't say it before, but I am using a Precision Piezo Universal, not an Orion.

  • In re-reading you original post, does the blue LED on the amp board still trigger with only a light touch? If so, your mounting is fine and there's something going on in the interface to the Duet. Can you confirm that you're using the probe connector, it's correctly wired, and M558 P8 (digital mode)? What's the value of the Z-Probe display in the DWC when there's no pressure? What does it jump to when you lightly tap the nozzle?

  • @tbluml said in Precision Piezo sensitivity on Duet Ethernet 2:

    I am using a Precision Piezo Universal

    That's the schematic and the pot values in the post.

  • Interesting, old universal board uses "modern" TLC27L4 while new version 2.0 Orion uses deprecated LM324

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