Graphing with node red and signalK

[JD1]

The TX+ line goes to RX+ on the converter, the TX- goes to ground on the converter. Since the talker's output on TX- is grounded, it has to be to ground on the converter with the converter's RX- left floating.
In my case, the talker is a Raymarine E80 chart plotter, which seems quite popular. It uses RX+/RX-/TX+/TX- nomenclature but should use data/ground nomenclature instead. The E80 NMEA0183 end is optically isolated but the inexpensive converter from China to go to USB is not optically isolated. The RX- and TX- lines from the E80 need to go to the ground pin on the converter.

For those that are curious for the technical reasons, the converter input chips sense the differential between RX+ and RX-. Since RX- leads to ground on the E80, it effectively is grounded. The RX+ line of the converter then moves between zero volts and some positive voltage (around 8V in my case). The receiver chip can sense the differential between zero and 8V but can not properly decode the second state where both lines are zero. If the RX- end is left floating, it moves to +5V so the input chip sees 8V-5V or 3V in one state and 0V-5V or -5V in the second state.

I hope that makes sense ....