How to connect NMEA-0183 boat-instruments to an Rpi4 to use data in Signal KServer-Openplotter

[RobVerhoog]

Hello,

I'm new to the community and enthousiastic about DIY-projects, but not an engineer or developer....Hope I'm in the right place to search for some help.
I have started a project for my sailboat. The goal is to create a little network using the Rpi4-Openplotter distribution as a base. I have the Rpi running with Openplotter and SignalK server, etc. I can connect wireless from my laptop to the Rpi. Now, one by one, I want to connect the boat's equipment to the Rpi so that the Signal KServer can work with the available data.
My question is which is the best choice for me to connect various NMEA0183 instruments to the Rpi system. I have a Pican-M HAT with only 1 serial port available. On the internet I read about an 0183-to NM2K converter. But what can also be done is an RS485-to-USB cable for each instrument. I have 4x USB available on the Rpi. I prefer to use the SignalK-server power to handle with the data, instead of using more hardware components... See the sketch for my configuration. Thanks in advance for reactions.

[andyrbarrow]

Either option will work. OpenPlotter is fine at taking in NMEA0183 and converting it to SignalK, and then to NMEA2000 for your MFD. RS485 - USB adapters are inexpensive, or you can use a HAT on your PI that does both 2000 and 0183.

[RobVerhoog]

Thx Andy, see below for other reply's if you're interested.

[tkurki]

What is the MFD going to be? Is it going to need access to wind & depth & speed data? It does not appear to be connected to the NMEA2000 bus.

Seems like all your data is originally in 0183 format, why do you have NMEA2000 in the picture? Is it just for feeding power to the RPi?

Converting all 0183 to N2K then feeding to Signal K introduces the 0183-to-NMEA2000 converter. If it does what you want fine, but then you don't have access to the original data from the 0183 in case there is something missing in the conversion. With just these basic sensors you probably won't have any trouble, but that is kind of fundamental difference in the solutions.

There multi-port usb serial adapters that would take up only one usb port.

[sailoog]

Powering from a NMEA 2000 network is not a good idea, you can only take 1A from there and you will have to power many USB devices + Raspberry + MFD?

[RobVerhoog]

The 1A as maximum seems so low to me. Because my knowledge in electronics is low, I looked up some examples of networks on sailboats that are powered over NM2K. In the picture below you see on 1 N2K-backbone 7 devices that are powered over the N2K (the red lines have direct DC-power). I looked up the power consumed by each device in this picture on internet and I come to +/- 10W. Then I calculate for a 12V-system, 10W/12V = 0,8A.. The NM2K-powercable is secured on 3A. Can you explain why the 1A-max is the reason not to power to many devices over NM2K...? Thx.

[tkurki]

A concise summary: https://digitalyacht.net/nmea-2000-networking-guide/ => NMEA 2000 Network Current

Note that even devices with separate power source consume some current, for practical LEN calculations every device has LEN of 1.

[sailoog]

3A total and approximately 1A for drop cables are the maximums of the NMEA 2000 specification. We designed the MacArthur HAT v1.0 to be powered from N2K but we realized that a touchscreen + Raspberry (specially model 5) + USB devices will be easily over 1A, so we fixed that and now we power directly from battery in v1.2. This is why almost all MFD are auto powered.

[RobVerhoog]

Thx to all for the reply's. I'm a lot wiser now to make the best choices while I'm only designing and testing the basic configuation I have in mind. The MacArthur HAT cought my attention earlier but it's not on the market yet, caused by what you say about the RPi5...I look forward to when this fully-featured HAT will be released for users...
The summary link on N2K ins-/outs is very usefull as well.