Reefmaster Live - NMEA 0183

Hello Everybody,
I am completely new here, and found this place by googling as I am looking for a solution for the following problem: I have bought a Garmin Echomap 62CV (incl. GT20-TM transducer) because it can send out a NMEA 0183 signal which enables me to do a bathymetric survey with Reefmaster. I had intended to use a old laptop with two serial ports.

I connected ground and Tx (transmit) from the Garmin to the respective ground and Rx of the DB9 RS422 serial port through a OPTO-4 isolator (as advised by Actisense) as per below:

The strange thing is I am not getting any signal into Reefmaster, although with Putty I can see NMEA stream is being send out (ref below)

I tried all sort of settings, different laptops and even a serial to USB adaptor but the GPS and depth sensor data is just not coming through. I cannot ask a question on the Reefmaster forum which can not be accessed due to some strange bug (please complete CAPTCHA which is not being generated)

Is there anybody who perhaps could advise me what could be the problem because I am about to throw in the towel

Thanks a lot


Data being received:

$PGRMM,WGS 84*06

The power cable of the Garmin has the NMEA 0183 functionality build in by providing the Rx and Tx ports as follows (the NMEA 2000 signal comes straight out of the back through a separate connector) Below snapshot is from the manual

My set-up:


@oaamaas may be able to help

If it’s working on Putty that’s a good sign. Make sure reefmaster is set to the same port and baudrate, and also that Putty is closed or disconnected before reefmaster tries to use the port.

On the reefmaster side, is it set to read the GPGLL message? The configuration shown in the docs here make me think maybe the default is GPGGA for position which isn’t in your sentences. Make sure that reefmaster is looking for sentences that your gps is sending, or that your GPS sends the sentences reefmaster is looking for.

Also the SDDBT sentence has a blank for the actual depth numbers so maybe it needs to be in the water and reefmaster is ignoring it until the data is good? See example of a good sentence here.

Finally your SDDBT sentence has no * which is the separator for the checksum, that is weird too and could cause reefmaster to ignore it, I assume reefmaster uses that and commas to parse the data but don’t know for sure.

I don’t know if any of these are the problem, let us know if you get it working!

Thank you very much Mike!

Reefmaster is set to read both the GPGLL and GPGGA messages, but you are correct as in my example I did not send the GPGGA. I am making sure I am reading what I am sending.

The SDDBT sentence is not giving proper data indeed, probably because I am testing it in a bucket with only 40cm of water. Howver, it does display a value on the Garmin (1.2m) but apparently does not send anything out in NMEA 0183. (Also the live screen is very crappy and scattered)

But even so, Reefmaster should be able to read the GPS (without getting anything usefull in for depth?)

With regards to your last remark , its strange indeed that there is no checksum separator in the example I send, but in below example it is present (p.s. I now I only allow Garmin to send DBT, GPGLL and GPGGS)

Kind regards,

data dump NMEA 0183


p.s. I see a very strange effect in my editor as checksums do not always appear, I will show screen-dump of what I see, seems to be a bug in the forum software? Which makes me think there were checksums also at the previous example only not showing?

My Reefmaster screen :sob: :sob:

And you are sure that baud rate of 4800 as configured in Reefmaster is correct? Ref Mike’s suggestions.

Hi Olav
I am certain of it, the Garmin Echomap 62cv has four communication options:

NMEA Std (4,800 baud and selected)
NMEA High Speed (38,400 baud for AIS)
Garmin Standard
Garmin High Speed

This is confirmed with Putty because it only gets the NMEA sentences when I set the baud rate to 4,800

I really don’t understand what the heck is going on

Thanks again

I’m at a loss. You are pressing the “connect” button right (joke)?

I guess I would try to get some good data on the DBT sentence to see if that is required for location to be used as well, even though there are separate indicator lights. You could either take the rig to some deep water, or program something like an arduino to serial print a sentence from one of the examples on the internet and your GP sentences too. I have code that creates the NMEA string from a windvane you could hack if you wanted to get fancy and generate checksums etc. but just printing a known good sentence is easier.

Also out of superstition I would set the GPS to send the RMC sentence and use that in reefmaster too, it’s the best sentence in my opinion, but there is no reason this should be the issue.

I don’t use reefmaster myself so could also be missing something obvious.