Hi, lately I've been thinking about using CAN bus to send data to and from the xy carriage on my 3d printer to reduce the number of wires needed to control the hotend.

To do that I need to get some data (fan speed, set hotend temperature, step and direction signals for extruder stepper driver etc . . .) from the control board running Marlin firmware to an STM32 board that supports CAN bus witch will send it to another board on the xy carriage over the CAN bus. The CAN bus stuff should be relatively simple but the main problem I have is getting that data from Marlin.

I'm thinking I could use I2C to get that data out but the firmware is rather large and I don't know where (in what file) to get that data from. Can anyone here offer some good advice?

You could save yourself a lot of work by using a Duet 3 Mini main board and a CAN-connected Duet 3 Tool Board. [docs.duet3d.com]

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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].

... or insert an ESP32 Devkit inbetween -- could even replace most of the "high level" functions

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

I thought about that but it is solution for single extruder only and it only works with the duet board.

Ok, so I've found it in the Marlin_main.cpp file. I've made it to output the set hotend temperature and fan speed, but I can't get the extrude distance out over the I2C. Does anyone have any idea as to how to do that?