Piezo probe not working
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I've noticed that if you have to press hard by the bed, then your piezo is wired backwards. I haven't figured out a rhyme or reason why this happens, but I have had similar issues where just switching the piezo polarity fixed those problems. Not really sure, I have 4 hotends wired the same way and 3 want the piezo wired backwards to trigger properly and 4th wants it wired normally.
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I can shed some light on it. When the polarity is correct the circuit detects the first rising edge of what is an AC electrical pulse generated by bend/compression in the PZT ceramic. If its inverted the first edge is not detected as it essentially is inverted, but the rebound second wave gets picked up instead a few ms later resulting in a dull, heavy contact.
However, I think with zerogee's issue since a light finger tap up on the hotend gives a trigger its probably the right way around.
There is another sure-fire test. Press upwards firmly and keep the pressure on, and see if you get a trigger as you push up, then release the pressure and see if you get a trigger when you let go. If you get a trigger on release this is a 100% diagnosis of the wrong polarity.
Certain implementations can change this behaviour if the piezo is bent in an unusual way for example. In this case, try both ways around and select the most sensitive or change to a more predictable mounting. Compression works well for underbed, bending works best for hot ends.
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So DjDemonD is correct, when i tap lightly on the side it triggers But i did try pushing straight up on the hot end as the bed would do but it did not trigger right away. I did not notice (or wasn't paying attention) if it was triggering after a lot of upwards pressure or maybe triggering when i started to let off. either way I'm going to try and reverse polarity, as kazolar suggested, tonight and see what happens.
thx guys. -
DjDemonD, on another note, i did speed up the bed probe speed to your suggestion of 420 mm/min and it seem to help a little, but the bed is still pushing way to hard to trigger.
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I have my probe speed at F100. Don't think going faster should be necessary. These things are very sensitive, you want it to trigger as soon as it taps the bed. I've had the same thing happen with 2 setups. I can touch the nozzle and see it trigger, but the it is compressing way too much to trigger when testing. Since I already seen this behavior with my other printer and reversing polarity worked there, I tried doing that this time and was able to find the orientation it liked where just the slightest tape of the bed triggered it. Very happy with these boards. And my configuration is far from simple. I have 4 hotends each with piezos in my custom designed extruder mounts on the same machine, and it works beautifully, each hotend is able to trigger the probe, so I was able to get z offset calibrated for each within a few microns. Next is to figure out if I need to calibrate a mesh for each hotend.
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Zerogee just reverse the piezo polarity then retune with vr2 (or left pot if on Piezo20 pcb) and see if it helps. Let's rule it out.
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Kazolar be nice if you could probe a mesh then define an offset for each nozzle.
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Kazolar be nice if you could probe a mesh then define an offset for each nozzle.
I'm going to try it – just having some issues with homing which DC42 is fixing. Moved my Z axis to the Duet of from the external drivers -- feels a lot more precise. Looking forward to seeing how the precise the probe is now.
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so switching the polarity worked. it now triggers with a light touch of the bed. But now my x axis move is all crewed up. I haven't changed the code except for turning on the power when i got home, now x axis is screaming across the axis. if i select a 1mm movement if move about 20mm VERY fast. I going to move this issue to the appropriate section. as for the probe i consider it fixed.
thx everyone.
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Great result with the probe sounds like steps/mm or microstepping are wrong for x.
