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How to determine device protocols
I have OP installed on my Pi 3B+ with a Sense Hat, am learning Node Red and starting to make progress. I'm trying to figure out how to get my knot meter into the mix. 

My sloop has a traditional thru-hull paddle wheel knot meter, and I have climbed through all the documentation I can find without locating a single reference to its communication protocol. Do I assume based on its era of manufacture (late 80's/early 90's) that it is NMEA 0183? Do most devices include the protocol in their documentation, or is there a better location or method to determine it? 

Here is a link to the device in question - any help appreciated on how to register it in OP:

and THANKS to everyone who is contributing here! Great stuff!!!
It uses a reed type switch or similar. It sends a pulse every rotation i guess. The voltage will have to be checked a but if you can get it below +5v it could be read via a digital pin on the RPI. I would look at wind speed sensor code for some ideas.
Look here

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(2019-02-19, 01:04 AM)Igetit Wrote: through all the documentation I can find without locating a single reference to its communication protocol.

The communication between the padle wheel and the log is probably very basic : the pulses of the padle contact ! One way to check that is to use an analog mulimeter like  this one
At low speed you should see the beat of the needle at the rytm of the pable revolutions...
Then you may have 2 possibilities :
- connect  the signal (with great precautions -level adaptation) to a GPIO pin, and code ...
- go for an airmar DST800 which offers a NMEA output - both NMEA 0183 and NMEA 2000 versions exists ...
If you are lucky, as a bonus, you may be able to connect its paddle signal to your existing log (to be checked in the doc, level adaptation may be necessary) ...
Didier B
Pi4, SSD USB3, OP 2.6.2, OC  5.2.4


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