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Assembling a Wire harness for a CAN Bus with 3 or more devices.

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joewiki

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I'm working on a car project where I need to connect multiple devices ( more than 3) to the same CAN bus. One of these devices is supposed to go in the engine compartment and the rest of them inside the car (possibly as far as the trunk). Each device is an electronic board, like the CAN-BUS-Shield-V1.2 for Arduino, with screw terminals for the CAN-H and CAN-L signal wires.


Specifically:


(1) How should I make a 3 way connection to tap a device into the bus? Do I need any special connectors? I've search for Female-Male-Male DB9 Tee-connectors, but can't find anything online. What about M12 or 5 pin mini Circular connectors? Or doing soldered Tee splices (maybe Y splices).

Please include links to any online parts you would recommend.


(2) Any special wire/cable characteristics to look for such as..

- Gauge (considering that the signal has to go from trunk to engine compartment)?

-Shielded cable vs unshielded twisted pair?

- Characteristic impedance?

Again, links are greatly appreciated.


(3) All of the boards already have the CAN signals connected with 120 ohms resistors, but those resistors can be switched out. I understand that two and only two terminations should exist between the two CAN signals . Should I consider switching out the resistors in the boards, and instead use external 120 ohm terminators?


(4) Lastly. I never done any hands-on work. Anybody has an idea how to run wires through the firewall?. The car we are working on is a Kia Soul.


Please note that this CAN bus is separate from any CAN bus already in the vehicle and has nothing to do with the OBD connector that is found in the vehicle's cabin.


Thanks so much
 

dr pepper

Well-Known Member
Most Helpful Member
Doesnt really matter what connector you use, obviously under the bonnet it would need to be airtight and water resistant, 9 way D types are sometimes used for can, I'm pretty sure theres a standard pinout for it too.

Shielded might be a good idea, it depends on the value of pullup resistors the car has on the bus and the amount of noise present, twisted pair for a car length probably isnt required.

Are the resistors in series, pullups or pulldowns?, if the canbus is independent then if they are inline switch them in it will protect the line drivers.

Be prepared to have sore and cut hands!, the best way in my opinion is to find an existing rubber bung in the bulkhead that doesnt have any wires through it, theres usually a couple, and use that to put the wires through, if you drill a hole in metal/plastic its important to use a rubber grommet.

Vehicles these days often have 2 canbuss's, a low and a high speed, the former for body systems and the latter for the powertrain.
 
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