rhaine
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Receiving NMEA sentences from Garmin Echomap

Thu Dec 31, 2020 2:52 pm

Background: The original Raspberry Pi in 2012 has been used successfully by Biologists in the past connecting a Garmin Echomap GPS fishfinder to record NMEA 0183 sentences. Using the shared data wires from the Garmin (RX/TX) and a serial to usb cable bathymetry has been performed on lakes.

I've connected an RPi 4 to a Garmin Echomap's shared data cable and cannot receive data with GPSD. I'm using a TTL to serial converter and a USB to Serial connector that uses the FTDI control chip. I've tried every recommendation but GPSMON and CGPS will not read the NMEA sentences.

any ideas would be most appreciated doing research in Florida.

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joan
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Re: Receiving NMEA sentences from Garmin Echomap

Thu Dec 31, 2020 6:32 pm

How have you tested each piece of hardware?

rhaine
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Re: Receiving NMEA sentences from Garmin Echomap

Wed May 05, 2021 5:27 pm

So sorry for timely responding. I wanted to get more complete nformation before posting hardware status of everything.

I successfully connected the Garmin Echomap 63cv to the Raspberry Pi and was able to retrieve NMEA 0183 sentences and record them on Florida canals. In answer to your question, I found a simple Serial to TTL converter. The Garmin only requires the black (GND) and the blue (RX) connected to the converter GND and RX pins to work. The converter module that worked was the DZS Electric RS232 DB9 female to TTL Converter Max232. I connected this to Plugable's USB Serial Adapter. When connected the tiny LED on the converter pulses every second as it is receiving the NMEA Sentences. With GPSD I was able to record data from the Garmin on a boat using their GT24UHD transducer. We collected GLL and DBT sentences in order to map the canal depths (Bathymetry).

I've learned these Serial to TTL Converters are not all created equal. Either Prolific or FTDI appear to own the chip industry in China. You never know if you're getting the real stuff or clones when you purchase on Amazon. it took me (8) different Serial to TTL Converter modules before I got one that worked. So.............attempted to purchase another of the exact same..............and it didn't work.

Thus, I'm exploring different alternatives. I felt ADAFRUIT's hardware was more adaptive to the Raspberry Pi environment. Their 954 USB to TTL Serial Cable for Raspberry Pi would combine everything in to one cable from the Garmin to the Raspberry Pi's USB Port. I connected Garmin's RX to the white RX of ADAFRUIT cable and the black Ground to the black of ADAFRUIIT cable and it doesn't work.

dmesg | grep -i usb shows me the converter cable on ttyUSB0 so we know the cable hardware looks ok
here are the commands I ran with the Serial to TTL converter module that work and give me the NMEA data

sudo systemctl stop gpsd.socket
sudo systemctl disable gpsd.socket
sudo gpsd /dev/ttyUSB0 -F /var/run/gpsd.sock
gpsmon /dev/ttyUSB0 (doesn't work. This is the command that gives me all the right NMEA data from the Garmin)

why doesn't ADAFRUIT serial to usb cable work for me?

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scruss
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Re: Receiving NMEA sentences from Garmin Echomap

Wed May 05, 2021 6:21 pm

I connected Garmin's RX to the white RX of ADAFRUIT cable and the black Ground to the black of ADAFRUIIT cable and it doesn't work
You want to connect the Garmin's TX to the Adafruit Interface's RX, otherwise nothing will be received.

Do you still have details of how you connected the Echomap to the original Raspberry Pi? What did you change to make it stop working?

I'd start from basics: is your chartplotter sending NMEA signals? Looks like Garmin use 5V TTL, and they recommend using a multimeter to check for signals: https://support.garmin.com/en-CA/?faq=7 ... nT69kmSXH6

If you have a MAX(3)232 in there, what comes out of the 9-pin serial connector is not a TTL signal. You'll need an RS232 to USB interface to get the signal back to something usable.

Raspberry Pi OS is pretty good at detecting serial interfaces. I've never found an FTDI or Prolific (real or knock-off) that didn't work with it. More of a problem is working out if the interface shows up as /dev/ttyUSB0 or /dev/ttyUSB1 or ... If you have only one serial device connecting, it will almost always be /dev/ttyUSB0

Is there a /dev/ttyUSB0 device showing up on your system?
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scruss
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Location: Toronto, ON
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Re: Receiving NMEA sentences from Garmin Echomap

Mon May 10, 2021 6:19 pm

Is this the same question as your other one: Garmin ECOMAP connected to RPi 4
?
‘Remember the Golden Rule of Selling: “Do not resort to violence.”’ — McGlashan.
Pronouns: he/him

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