Openplotter/MacArthur Hat and Volvo Penta Multilink Interface

[Chuncky]

I've spent the long winter playing around with a raspebrry pi 5, MacArthur Hat and some signal sources, creating KIP dashboards.  So far so good, albeit very slow due to my lack of experience in this area.

As a next step I'd like to display my engine data on a kip dashboard.  We replaced the engine on our boat a couple of years ago, so it's a recent (2022) Volvo Penta (V-P) D1-30 with EVC and multilink interface.  It's a very simple network, with a 'black box' on the engine (V-P call it the MDI) and a canbus (V-P speak: 'multilink') cable linking this to the integrated rev counter and small alphanumeric display.  I've sourced a few 6-pin Deutsch connectors (2 x male + 2 x female) with the intention of creating my own Y-connector instead of the expensive Volvo Penta equivalent (part no 3588206) to extend the canbus to my raspberry pi/MacArthur hat.  

The V-P system wiring diagram is here:

https://i0.wp.com/cdn.webshopapp.com/sho...?strip=all

Questions:

1.  Is it 'simply' a case of connecting the Can Hi and Can Lo conductors into the relevant terminals on the Pi/MacA hat?  Once that's done do I access the engine data via something like canboatjs?  OR, do I need some interface hardware?  (I'm not on the boat just now, so I can't check.  I'm also keen not to brick the Volvo Penta hardware).  I've seen a thread talking about this link using a J1939 protocol and additional ESP32, but I have to admit that I have no idea whether this applies to my system or not.

2.  I've found a thread here https://open-boat-projects.org/en/volvo-...interface/, but it's not connected to a MacArthur hat, so uses a canbus transceiver.  Is that required with the MacA hat?

3.  Canbus 120-Ohm Termination resistors - Do these exist on the V-P network?  Their diagrams don't show them anywhere (see diagram link abve) There seems to be no restriction in how the V-P instruments/parts are interconnected to include the termination resistors.

As our boat is pretty old now (30 years), we have no other NMEA2000 systems, so I don't have to concern myself with the implications of the above connections on those.

Any help/suggestions would be greatly appreciated.

[Adrian]

I hope someone else with actual knowledge of MDI will chime in, but here's my 2 cents:

From you second link, it looks like V-P is using regular CAN. However the project seems to use another microcontroller (ESP32) to translate the CAN messages of the V-P to N2K messages. N2K is also CAN, but defines standardized message types (datagrams) for specific information (like engine speed, temperature, etc.).

So technically, yes you can connect the V-P CAN directly to the MacArthur HAT. But there needs to be software (Signal K plugin?) that translates V-P CAN messages. If that doesn't exist yet, the linked project might be a good starting point, and it's only about 200 lines of Arduino code. The Signal-K forum or Discord might be good place to ask about that part.

Termination depends on the topology of your network. There are a few tips here on how to figure that part out:
https://macarthur-hat-documentation.read...00-network