NMEA 0183 Data from Lowrance Chartplotter Received as Garbage

[boybert]

Do you have correct polarity?

You can use an LED to check: https://digitalyachtamerica.com/download...4129&ind=0


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Thanks for the feedback and inspiration, tkurki!  The LED trick resulted in no illumination so I tore out the wires (which I had carefully aligned following instructions from both Lowrance and the RS-422/USB converter) and started attaching different combinations.  At the third or forth iteration, success! I am now getting good GPS and other NMEA data in and out of the Raspberry Pi, OpenPlotter, and OpenCPN!

For posterity, here is the configuration that is working for me:

Code:

+--------------------+--------------------+
|      Lowrance      |      DSD Tech      |
|    Elite-4 HDI     |   RS422 Converter  |
+--------------------+--------------------+
| Blue (TX_B)        | 1 (TXD+)           |
+--------------------+--------------------+
| Yellow (TX_A)      | 2 (TXD-)           |
+--------------------+--------------------+
| Green (RX_B)       | 3 (RXD+)           |
+--------------------+--------------------+
| Orange (RX_A)      | 4 (RXD-)           |
+--------------------+--------------------+
| Shield/Ground      | 5 (GND)            |
+--------------------+--------------------+

Not sure if I just don't understand the wiring or if one or both sides is mislabeled, but this is currently working, bidirectionally.
Thanks again all for the support.