Transmit sensor information over digital communication



  • Hello,

    My Delta printer is quite large (~1.5m tall) and has "sub-optimal" wiring:

    • Very long wires from effector to board (~2.5m)
    • Unshielded
    • Sometimes running adjacent to noise emitters like fan PWM

    While I am working to improve these issues, some are systemic and can't really be easily improved upon.
    I am also excited by the idea of implementing a strain gauge z probe, which would by design be a very delicate signal.

    Thus I have begun considering the following wiring topology:
    Sensors to some sort of "Analog to serial" device, plus a decoder board next to the Duet, or directly to the duet if it's possible to implement the SPI interface

    Sensors to some sort of "Analog to serial" device, plus a decoder board next to the Duet, or directly to the duet if it's possible to implement the SPI interface.

    Would be interested to hear your thoughts on the matter, and also recommendations regarding possible ways to implement this simply (i.e. smallest board, off the shelf components, etc.)

    My current candidates as an electronics newbie are various tiny arduino compatible boards to act as a2d+I2C transceivers where my hope is to lower the I2C speed in order to have it work with a longer cable length then normally accepted, but also thought it might be possible to utilize the Duet2-Wifi's SPI bus for this, but I'm not sure how (or if) it could be done.

    Thanks!



  • Just thought I'd add a few shots of the noise I'm currently seeing on the thermistor:
    2020-09-28 18_35_55-Goliath.png 2020-09-28 18_30_03-(4.7%) Goliath.png



  • Toolboard could be the solution here, at least for duet3


  • administrators

    The Smart Effector uses a strain gauge and converts the strain gauge signal to a simple digital signal to pass back to the Duet.

    BTW the HX711 is a poor choice for this application because it has a maximum sample rate of 80Hz, meaning that the time that bed contact is detected will have a jitter of 12ms. If you probe at 10mm/sec then this equates to a height uncertainty of 0.12mm.



  • @BoA said in Transmit sensor information over digital communication:

    Toolboard could be the solution here, at least for duet3

    Interesting, didn't know this existed! is CAN not supported on Duet2-wifi? I seem to see some references to CAN in the pinout table, but I'll admit it's not 100% clear to me....

    @dc42 said in Transmit sensor information over digital communication:

    The Smart Effector uses a strain gauge and converts the strain gauge signal to a simple digital signal to pass back to the Duet.

    BTW the HX711 is a poor choice for this application because it has a maximum sample rate of 80Hz, meaning that the time that bed contact is detected will have a jitter of 12ms. If you probe at 10mm/sec then this equates to a height uncertainty of 0.12mm.

    Definitely read your comment regarding the HX711 and that's why I linked directly to it. thanks for the tip! I plan to use an InAmp like you suggested.

    I would love to use the smart effector, but unfortunately that would require a large amount of changes to my design first and foremost as my carriages do not have a 55mm center distance - but I'll have a look at the design to learn how experienced designers tackled the issue.



  • @Leav there are quite a few adaptors on thingiverse for the smart effector when using different carriage spacing.
    I used one on my Anycubic Predator for quite a while before changing the arms too and that had a carriage spacing of ~60mm


  • administrators

    @Leav said in Transmit sensor information over digital communication:

    Interesting, didn't know this existed! is CAN not supported on Duet2-wifi? I seem to see some references to CAN in the pinout table, but I'll admit it's not 100% clear to me....

    CAN is not an option for Duet 2, you need to be running either a Duet 3 Mainboard 6HC or (when it is released) a Duet 3 Mini 5+.


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