NMEA2000

Here is some of the NMEA2K testing you can do with the sniffer:

Voltage Test – Ensure your NMEA2K system power supply is turned off. Plug the device into the NEMA2K port using the standard drop line cable (or a SimNet to NMEA2K cable). Connect your multimeter (set for DC Voltage) across the Red and Black power binding posts. Turn on your NMEA2K power. You should see a value around 12V. It will be higher if your electrical system is charging and lower if you are running of battery. While NMEA2K is tolerant of a supply as low as 9V, I would be concerned about bad cabling or connections if it was much below whatever your battery voltage is measuring at.

Termination Resistance Test – Ensure your NMEA2K system power supply is turned off (and leave it off for this test). Plug the device into the NEMA2K port using the standard drop line cable (or a SimNet to NMEA2K cable). Connect your multimeter (set for Resistance ) across the White and Blue CAN-L and CAN-H binding posts. You should see a value around 60 Ohms. 

Each end of your NMEA2K needs a 120 Ohm termination resistor. If these are properly installed then you will get a combined resistance (both 120 Ohm resistors in parallel) of 60 Ohms. If one of the termination resistors is missing then you will see a resistance of around 120 Ohm.

If you see a much higher resistance (possibly 50K Ohms or higher) then you may be missing both terminator resistors. If you see a lower resistance (say 40 Ohms) then you may have 3 terminators. Both of these conditions are typically problematic though if your boat has SimNet cabling and you add a SimNet noise filter you are effectively adding a third terminator (YMMV).

If you really want to get into the details of the various things you can measure for then check out the Maretron manual for their N2KMeter tester as it goes into a fair bit of depth of what values are allowable for the various signals.

NMEA2000 Sniffer – First download and install the NMEA Reader software from Actisense. Connect the USB cable from the ESP32 module to your PC. Take a note of the COM port it uses (you can check this using the Windows Device Manager). Fire up the NMEA Reader app and select the correct COM port and set the  speed rate to 115200.

Ensure your NMEA2K system power supply is turned off. Plug the device into the NEMA2K port using the standard drop line cable (or a SimNet to NMEA2K cable). Turn on the NMEA2K power supply.

You should now see the streaming NEMA2K data in the Data View window of NMEA Reader. You can see all the devices, the addresses they are using, the refresh rate and the various PGNs that they are using the send data. You can enable logging and it will save the data in a format that you can open later using the Actisense EBL Reader software.

NMEA0183 Sniffer – First download and install the NMEA Reader software from Actisense.  Since the NMEA0183 system is not a bus style backbone like NMEA2K you may need to disconnect your NMEA0183 device data wires from whatever it is connected to and ensure it is powered up. Connect a RS485 or RS232 to USB interface to your PC (depends on the version of NMEA0183 you are dealing with). Connect the RX and GND leads of the interface to the TX and GND leads of the NMEA0183 device. Select the correct serial port of your interface in the adapter in the application and adjust the speed to match your system (typically 4800 or 9600). You should now be able to view the streaming NMEA0183 data.

Saving A Capture – You can log and save the NMEA2000 (or NMEA0183)  data using the logging function of the NMEA Reader software and then review it later using the Actisense EBL Reader software.