I am working on doing this myself. There are some challenges.
Because the piezo sensors rely on movement, the larger the base that you can cover within the sensors, the better. I had a relatively small base for my bed size, and that ended up with unacceptable results.
So say that a piezo sensor requires 0.1mm of movement to trigger a response that the board can pick up. (Other options, like speed play a factor, too, but assuming that probe speed is constant, it will come down to movement.)
If you probe directly over top of a sensor, you'll need 0.1mm of deflection to register a touch. for anything that is outside of the polygon defined by your sensor locations, there will be an axis of deflection, probably made up by the two most distant mount points. We'll assume zero bending of the bed itself, probably close enough for the forces and spans involved on most 3D printers. For my old setup (I'm changing it to be better) it might be possible to probe 80mm away from a sensor, which in turn could be 80mm away from the axis line. In that case, it would require 0.2mm of movement to get the same signal. Actually, since it tried to use an axis of deflection in between 2 sensors, I found that I needed over 0.35mm of deflection in one corner, which was a clearly unacceptable deviaton over the surface of the bed. In addition, probing in the centre of the 3 sensors that I was using needed an even smaller deflection, almost zero, which would otherwise be almost ideal.
For temporary use, I decided to use a 3 point probing system, directly over each of the 3 underbed sensors, which resulted in useable leveling.
I am currently constructing a solution where I am stiffening the support, and placing sensors under the head bed mounting scews. 4 in a 209mm square, under a 220mm by 275mm heated build platform. It will still be possible to probe outside of the sensor polygon, but I will probably define my mesh leveling to stay within that polygon in order to achieve the maximum consistency in probing. I don't have results yet, I'm still in the actual build process for this.
Follow up update! I have submitted a revision to the Firmware, which hopefully will be accepted: https://forum.duet3d.com/topic/7151/linear-adc-thermocouple-improvements
It is indeed possible to use the MCP3204 or MCP3208 ADC chip with the Duet!
Once the firmware is updated, it should also be possible to use all 4 or 8 channels of ADC in either single mode or differential mode. (Right now, only 1 channel is able to be used at a time).
The circuit is very sensitive, contact with the screwdriver can cause triggering. I think that the potentiometer is damaged, I have sent you a replacement PCB. When the new PCB arrives, try your mount before adjusting the potentiometer. In most cases the standard position for the board as manufactured will work well enough to make sure that your firmware settings are good.
Here is my latest probe run after thoroughly cleaning the glue off of the plate and doing 2 probes per point with bed at 70c and hot end at 180. I also increased the trigger threshold to 600 so it hits slightly harder. And it now has a stiffer Piezo upper mount I printed in Taulman 910. My BuildTak magnet system will be here tomorrow. I ordered an extra steel plate so I can have a Buildtak and a PEI option. At this point I won't be attempting to make the plate any flatter than it is.
I did a calibration print for square, and it appears I'm good other than a fraction of a degree off 90 degrees Z to Y. So my Z uprights are not quite vertical.
You can connect up to 7 stepper drivers to the expansion connectors of the Duet. The outputs are 3.3V with limited current capacity, so we recommend you use this https://www.duet3d.com/DuetAddons/Expansion_Breakout to boost the signals to 5 external large stepper drivers.
You can use the M584 command in the boot-time configuration file to remap axes to your external drivers, and reallocate the spare internal drivers as additional extruders if you wish.
If I level my bed with the 0,15 mm metall sheet, my first nozzle height, if I print 0,2mm should be 0,35mm or?
0,15mm is the distance I gave with the metall sheet, where the printer thinks it is Z0
0,2mm for the layer height.
It is working fine. In the link is the code of the lcd where the leveling is coded.
I wonder where the gap of 0,15mm would be with my HEVO?
https://www.dropbox.com/s/ccreium22rki3cq/JGAurora A5 Custom LCD firmware - 20180111.zip?dl=0&file_subpath=%2FJGAurora+A5+Custom+LCD+firmware+-+20180111%2Fmks_config.txt
Thanks for the input, guys. I've since had a brief conversation with Haydn, and he stated that he hasn't had a single request for larger diameter arms in 360mm length or shorter. He did state he's done larger diameter with longer arms, though. He again stated that his normal 0.230" is plenty sufficient for 360mm & below, and likely somewhat longer, too.
I did see on his site that he recommends a dab of lube in each joint (he applies with a Q-tip). I think I'll try that soon.
@snowcrash said in FSR Controller Module for Auto Bed Leveling:
So, assuming I have version 2.01 of the firmware, I can use: M42 P60 S0/S1 to control pin CS5, and M42 P65 S0/S1 to control pin z_mod_probe? Is this correct?
Yes, but you will have to wait for 2.01beta3 to use M42 P65.