Happy New Year 2026 to everyone!
I accientally used NMEA2000 standard on M12-5 pinout, so I am adapting my power connector to be a M12-5 with Power and CAN.
NMEA2000 has a Power/CAN pinout as standard that I want to adapt to my ECU designs with the difference that I allow 8-36V rather than only 12V. The later gives me the option to use 12V or 24V, while the PSU tollerate 8-36V input. You also need some tollerance even on 12V since “12V” can be anything from 10V to 14 coming from a battery. What to watch out for is that we cannot mix 12V/24V components, so if we use other NMEA2000 devices we must be strict about 12V.
The 2nd change is bitrate. NMEA2000 bitrate is strict while I allow bitrates up to 12Mbps and CAN-FD as selected by user. In SW we have a NMEA2000 Compability Mode to use if this is NMEA2000. Otherwise we are more free to use what our design wants. I should warn that higher bitrates makes distance and multiple devices more of a challenge.
- Pin 1 : Shield
- Pin 3 : Power Input –
- S1 : Shield
You need to watch out for the 3 pins above. Pin3 is power and signal ground and a common mistake would be to connect the two shield pins on M12-5 to this. Shield should only be grounded in one end of a cable to avoid ground loops so this must be selectable to adapt to the design. CAN is very robust so it don’t normally need shielding, but automotive standards suggest shielding due to PWM signals and other noise that can create challenges.
The CAN port is in this case is isolated to 5000V++ while PSU itself is a bit lower. Isolated to 5000V means you can connect 5000V between pin 4 & 5 for 1 minute, sufficient to survive most EMI/lightning spikes.