51 lines
2.0 KiB
Markdown
51 lines
2.0 KiB
Markdown
# Working with CAN bus
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## Adapters
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You will need a CAN bus adapter for your Raspberry Pi (or other board you run klippy on). There are many options available.
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The adapter must support Linux socketcan
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### USB CAN adapter
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There is a very good open source firmware for STM32 based USB adapters, https://github.com/candle-usb/candleLight_fw. Any board running this firmware should work fine. There are plenty of open source hardware alteratives that runs this firmware.
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Get one at https://openlightlabs.com/products/canable-0-4 or find a clone on aliexpress.
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Innomaker has an USB CAN bus adapter widely available. It had a firmware bug that was reported and fixed March 2020, newer boards should have this fixed.
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### MCP2515 based CAN HATs
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The MCP2515 is a very common SPI connected CAN bus chip. It is a pretty bad options since it has very small buffers on chip and creates a lot of CPU load on the Raspberry Pi, and has a tendency to drop packet. It is not recomended if you use more than 1 or 2 boards or if you plan to use the accelerometer.
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You have to run the CAN bus at 250kbits/s or possibly 500kbits/s. An older Pi, or a Pi Zero will not work reliably, it has to be a Pi3 or Pi4 or better.
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An easily available option is "Waveshare RS485 CAN HAT"
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TBD: Is the MCP2517/MCP2518 based HATs any better? They are made for CAN-fd but are backwards compatible. As the drivers are not in the mainline kernel it's non-trivial to get an MCP2517/8 to work.
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## Linux and Klipper setup
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Please read https://github.com/KevinOConnor/klipper/blob/master/docs/CANBUS.md
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## Wiring
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### Cables
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CAN bus is a bus, it must be terminated at each end with 120ohm resistors.
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Twisted pair ... Ethernet cables or specifically made CAN bus cables. If shielding is used it should only be grounded at one point.
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As we run default at 500kbits/s each stub length can be up to 1.6m long.
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