Selecting wiring hardware for CAN network

by Maple   Last Updated August 16, 2019 18:25 PM - source

I'm having trouble selecting wire, jack and plug for small (up to 6 nodes, 3-4 m) CAN network. Each node will have 2 jacks wired for pass-through and short patch cables will be used to daisy-chain them together.

Previously, we were using CAT5e hardware with 100 Ohm termination for wiring CAN and 26V power. While not exactly up to 120 Ohm CAN spec, it worked just fine for such a short network and was really on a budget.

Right now we are trying to reduce the dimensions of some components and those RJ45 jacks come out as too big. So, the idea is to use 6p6c RJ25 connectors and 3 pair twisted cables. This gives us the same twisted pair for CAN and two pairs for power as before, but in much more compact package.

The problem:

Unlike CAT5e hardware, there is next to zero impedance data on alternative components. For example, here are some parts I've found on digikey: jack, plug, cable. I might be able to calculate wire impedance using one of the online twisted pair calculators and approximate dielectric constant for polypropylene, but this seems to be rather guesswork. I have no idea how to even approach the same question for jack and plug.

The question(s):

Is there a way to find out impedance for those components? Do such components even exist in the desired impedance range (100-120 Ohm)?

And more generic: how do you approach a task like this? I don't believe every engineer who needs to establish communication between two devices bothers with such low level details. Most likely they would use off-shelf components and focus on the software/device functionality.

Unfortunately, unlike Ethernet, the CAN networking solutions seem to be overpriced and oriented on industrial shoppers buying in bulk. Way out of our price range.

Tags : can


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