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simple question with a probably complex answer, can I extend a cars CAN network and wire in additional sensors to it? If yes can I get pressure and temperature senders for a CAN network (oil, water etc)

I am thinking about using a Raspberry PI and a CAN Bus connector to make a display, and along with what might be available I want to add some additional information that the ECU might not provide.

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As you wrote, this is a complex problem.

  • From the electrical side there are restrictions on the length of the CAN bus cable, and in general, one should avoid stub cables from the main cable. At work, I have an automotive CAN bus working at 500kBaud, which allows for 100m cable length. I doubt the cable in a car is that long, so extending it a little should work. Also, if a stub cable is not that long, it should not be a problem.
  • Of course, all devices on a network have to use the same speed setting. You can't run a device at 125kBaud while the rest on the bus uses 500kBaud.
  • Each device on a CAN bus has a node ID, which is the address used to communicate with it. Your new devices should of course have IDs which are not yet used by other devices on the same bus.
  • Consider how busy the bus already is, and if it could handle the additional traffic
  • You need do know how to communicate with all the devices, i.e. what bytes do send so they send back their data. This is especially important for the ECU, and you don't want to confuse the ECU.
  • Finally, today there's often more than a single CAN bus in a car. Be sure to know which cable belongs to which.

As you see, it's very tricky, especially since it's quite impossible to get some information about this.

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  • Thanks for the info. Thinking about it it might be safer to run a separate bus for my additional sensors. – Rob Sep 14 '18 at 0:46

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