driving via canbus Eltek 2kW Flatpack2 supplies

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Joined: 02/02/2017
Location: Australia
Posts: 1117
Posted: 02:55am 29 Mar 2020      

Another project that I need to get going is to develop some custom code and hardware
to control a number of Eltek power supplies.
Wiseguy and I have been looking at a problem he has.
Commercial products are available that can and do control these supplies
via canbus. But our needs are special so it means do it yourself.

Step 1
get some SPI to canbus transceiver boards. Connect one to an Arduino Uno.
Note well that canbus transceiver earth/ground needs to be tied to Eltek supply DC output ground

step 2
observe data flows.

I am stuck at step 2

Here is what is on canbus High and low wires. This is output even if the
canbus transceiver is unpowered. I have 200R termination present and when absent
there are spikes in the hi/low or low/hi transitions as well as rounded risetime.
So the termination resistors stay.

it is 125KHz canbus speed.

and the supply spits this particlar data stream out continuously
Here is the signal. No idea what it means.

Anybody here know much about canbus?
Is this signal suitable for input into the MCP2515 canbus transceiver chip
to be detected correctly and converted to data?
wronger than a phone book full of wrong phone numbers