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RepRap (Duet2 Wifi) Precision Piezo too slow?

Posted by jlimburg 
RepRap (Duet2 Wifi) Precision Piezo too slow?
November 17, 2021 04:18PM
Hi all, i have a Duet2 Wifi and have the precision Piezo setup as Z Probe as well as Z end stop. Duet is 1.04c, RepRap is 3.3.
Now i have two issues, one is with the time it takes the firmware to realize that the piezo is triggered (blue led on/flickering), the other is with the values read from the Precision Piezo PCB. When i set up the probe as analog (P1) the Z Probe field in the dashboard hovers around 503 untriggered (red LED on). Then when it is triggered, the values go higher, but just for a very short time, then they go into the 400 values. The firmware will trigger the Z Probe on this, but like i said it takes quit long and so the bed will already be higher than it should be, and i have to work with Z offsets of 1.9 or such. My threshold is 510. When i switch to digital (P5 / P8), the Z Probe value on the dashboard will be 0 when untriggered and 1000 when triggered, which is ok, but it still takes too long until the firmware processes the trigger. I can see the blue LED come on while homing Z and another maybe half second will pass until the firmware reacts.
I tried switching the polarity of the disc itself as connected to the PCB but that made no difference.
Hers an excerpt from my config.g:
; Endstops
M574 X1 S1 P"xstop" ; configure switch-type (e.g. microswitch) endstop for low end on X via pin xstop
M574 Y1 S1 P"ystop" ; configure switch-type (e.g. microswitch) endstop for low end on Y via pin ystop
M574 Z1 S2 ;P"zstop" ; configure Z-probe endstop for low end on Z

; Z-Probe
M558 P1 C"!zprobe.in" H3 F50 T6000 ; set Z probe type to unmodulated and the dive height + speeds
G31 P510 X100 Y100 Z-1.7 ; set Z probe trigger value, offset and trigger height
M557 X15:265 Y15:265 S50 ; define mesh grid

I would appreciate any help with this!

Edited 2 time(s). Last edit at 11/17/2021 04:22PM by jlimburg.
Re: RepRap (Duet2 Wifi) Precision Piezo too slow?
November 21, 2021 05:50AM
The response time of the Duet when the Z probe input changes is a few milliseconds when in analog mode (M558 P1) or filtered digital mode (M558 P5), and no more than 1ms when in unfiltered digital mode (M558 P8).

My best guess is that you have a bad connection between the piezo output and the Duet Z probe connector input pin, so that it is taking some time for changes in the signal level to leak through to the input pin. This is most likely due to a bad crimp in the cable. However, It could also be caused by a poorly soldered connector on either the piezo board or the Duet, or a poorly soldered input series resistor on the Duet.

Can you confirm with a multimeter that the voltage on the input pin on the Duet follows the state of the blue LED on the piezo?

For faster response to questions on Duet or RepRapFirmware, post at [forum.duet3d.com].

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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