Dms Load Cell Deut 3 6HC

Anawandur

Hello,
i am planning my own printer. Since I want different nozzle diameters, a Biqu Hermit Grab is installed so that I can easily change the print head. Since the nozzle has a different Z height when the print head is changed, I don't want to measure this via BL Touch but via a DMS load cell directly via the nozzle. I couldn't find anything about this in the documentation. Can you tell me if sawas works at all?
Many greetings

droftarts

@Anawandur Can you post a link to the specification sheet of the load cell you are using, and how you want to wire it to the 6HC? Most likely it can signal an analogue output of 3.3, 5 or 12V (the inputs on the 6HC can cope with up to 30V) or digital output (on/off) which can be read by the 6HC.

If it works like an NPN or PNP probe, see https://docs.duet3d.com/User_manual/Connecting_hardware/Z_probe_connecting#npn-output-normally-open-inductive-or-capacitive-sensor

Ian

Proschi3D

@droftarts

https://www.reichelt.de/entwicklerboards-a-d-wandler-waage-10-kg-debo-hx711-10-p316339.html?PROVID=2788&gclid=CjwKCAiAkrWdBhBkEiwAZ9cdcLFM3DD1dQWSU0LuUAF_v1Psl3LpLEHYqo34M-Dr-wWQQkWzFB5PzxoCVAMQAvD_BwE&&r=1

droftarts

@Proschi78 I don't have any experience connecting a load cell and/or sensor board to Duet. There are some other threads on the forum about load cells that may give you ideas:
https://forum.duet3d.com/topic/9081/load-cell-for-z-probe-and-hot-end-pressure-messuring
https://forum.duet3d.com/topic/24349/load-cell-z-probe
https://forum.duet3d.com/topic/25211/load-cell-data-acquisition-with-duet-3-6hc
https://forum.duet3d.com/topic/26334/duet3-6hc-load-cell-amp

Generally, the approach seems to be to use the load cell and sensor board connected to an Arduino board for collection, then pass the data to the Duet. However, this may not make a very good Z probe, as the response time may be too slow. @dc42's advice here seems to be about the best for a direct connection: https://forum.duet3d.com/post/262562 but it's only measuring a spool weight, and fast response from probing isn't a requirement.

Ian

dc42

@Proschi78 as @droftarts says, we don't recommend load cell amplifiers based on the HX711 chip for use as Z probes because of the slow response time. Also these devices are normally used with the offset voltage zeroes immediately before use, to compensate for any temperature-induced drift.

As a Z probe needs fast response time but only needs to detect a sharp change in load, it's better to use a low noise op amp to read the output from the sensor instead of a load cell. You could take a look at the schematic of our Smart Effector to see how we do it. The Smart Effector uses an on-board microcontroller for signal conditioning and to perform self-test functions, but for a basic Z probe you could probably use just the voltage regulator and op amp.