Anyone sending Signal-k from Arduino?

[LarsD]

Using ratiometric cable and voltage signal..   if the cable is bad  the wind speed will be 0, and the direction random.   It is usually obvious there is a problem if the wind direction never changes.

It is nice to detect a problem in the cable.  It is annoying to read 40mA though.   Unless you have an amplifier and low ohm resistor, you need at least 30 ohms.   This wastes quite a bit of power, up to 100mW, not to mention losses in the cable.

It might make more sense to put the uC in the sensors and send digital data down the cable.

For wireless...  I don't really like it, because you already need a cable to supply power.   Maybe 2 wires instead of 4, but wireless links also may have lag which can be bad and may be difficult to diagnose problems.

For signalk vs nmea0183...  You probably are going to want both anyway for the foreseeable future.  kplex converts nmea0183 to signalk.  So for this reason, unless you have more interesting data than only speed and direction, what do you gain by using signalk here?

For wasting a usb port.   It's possible to use any pin on the raspberry gpio header as a virtual serial port.  It consumes a few % cpu, but it isn't really an issue with low data rates especially with 4 cores

pypilot can get the wind data from different sources, It can receive from opencpn, or kplex for example, but this adds lag.  lag is bad in the autopilot control loop, so for this openplotter defaults to setting kplex to read the wind data from pypilot which reads the data directly from the sensor on a serial port. So the autopilot has it first.   If you don't use the autopilot, then it's not important, and can be configured differently.

Thanks for your reply,
OK, the lag might be an serious issue as you say - I hadn't understood that you "squeezed" pypilot in between the windsensor and openplotter - I assume it is still ok to run the main pypilot sw on the same RPI3 as where openplotter/OpenCPN is running?
 - Are you handling the GPS in the same way?
 - What about the rudder sensor? I'd like this data also to be available to OpenPlotter - do you send that onwards??
 - How do you interface the motor controller - is that also nmea? In that case I will be short of one USB/RS422 adapter and need to share with the AIS tranciever...

All my other sensors on the boat will use WiFi but if this would be an issue for wind then cables it will be.... I just got my 4 port USB extension for my RPI so I guess I could "afford" nmea0183 for wind. (1 for my AIS tranciever, 1 for the VHF, 1 for my STD Horizon plotter, 1 for wind instruments, 1 for GPS, 1 for kbd/mouse - that's 6 -> one spare - two if/when I retire the old plotter)

I thought you used signalk converted data in pypilot so I didn't think signalk was an issue but if you take nmea directly then I agree that doing a diversion through signalk makes no sense.... This would make use of one of my Arduino Nanos  in the first place anyhow....

On the wasted power issue, in my current test implementation i use the Arduino VCC as reference but I planned to turn to the internal 1.1 V reference and with 40 mA max current that would be like a 25 ohm resistor and if i didn't go absolutely wrong that would mean around 40mW + losses in the cable - assume a few more ohms there - say 5 -> 44 mW --- Not so bad.... 

How did you get to 100 mW?? Perhaps I've missunderstood something....