Speed-Data directly from Sensor

[michael.trilling@gmail.com]

Hi there,

I'm a total newbie to this whole think. But now - after some weeks of learning - I've made myself a OP Sailcomputer.
The whole thing sits in a watertight case, having a step up/step down converter for power and a USB-Hub for internal
connections.

Photos here:

https://drive.google.com/open?id=1_aU9Ev...0wGgJ51YPA

https://drive.google.com/open?id=1hwZKbc...vcTAaL8unw



There is a USB-Plug, a Ethernet plug and a HDMI plug at the side of the case.
Here I have Internet conection over the Ethernet, coming from a Ubiquiti Bullet M2 and a Antenne which connects to harbor wifi.
The HDMI plugs in my monitor on board and the USB-plug is used to connect via another hub the GPS, AIS and the AP.
Cirrently I'm waiting for Jean's weather sensor and his AP-controller for steering my Simrad TP22.

Besides Monitor and Keybord at the chart table, I have a 10" tablet in the cockpit under the sprayhood with a VNC-Viewer.
Also I have a small mobile in a arm pouch, on which I have the polar data, the ideal course to the appearent wind and all tactical data.
I use sailinstruments and the nke app.

One of my problems was, how to get the data from my old speed sensor into the system. The old Bidata ST30 is working with seatalk and my first idea was to use a seatalk to nmea converter. I found some code on the internet I had to alter a bit and programmed my arduino, but it was not working out.
Then, instead of buying a converter cable for 100 bucks, I thought of getting one step deeper into the system.
The speed sensor is a hall sensor.Three wires. You put voltage and ground in and recieve a signal in the same voltage on the third line whenever the little wheel in the water spins.
Luckily I found a ready to use C-scetch for the arduino that reads this signal and makes a nmea string from it:

http://www.holdentechnology.com/2017/09/...eedometer/

Easy to install on the arduino. Only thing left was the issue of the ST30 using 12V and the arduino only working with 3,3V-5,5V. So I used a selfmade voltage devider, that gets everything from 11v to 14V and devides it down by 3.

Now I have a simple Y-split in the signal cable and the data is still on the display of the Bidata ST30 and additionaly as nmea data in the OP.
Works fine when my wife is simulating the water current and spins the wheel under the boat. ;-)) Can't wait to use it in the water and calibrate it. 

Its not my invention. All credits go to Mr Mike Holden and its code. But maybe it will help anybody here with the same problem.