[AllyCat]

Many thanks, perhaps a good one for the FAQ   [or the Wiki]

Yes, +1.   I also had to "find out the hard way" that the Wind cable connections of the Davis need to be modified.

The problem is that Fine Offset and Davis have their Anemometer pulse (digital interrupt) and Direction Vane (Analogue) input connections swapped in the RJ11 plug.  With some microcontrollers this could be "fixed" purely within the software, but unfortunately the Arduino (Nano) appears to use separate dedicated pins for Analogue and Digital inputs.  It might be possible to "double up" (link) an analogue and digital pin (CMOS inputs have a very high input impedance) for each signal, but the Nano appears to have very limited interrupt capabilities (only two pins, one for the Anemometer the other for Rain?).  So it looks as if a (PCB) switch/link or plug rewiring may be the only solution.

Another difference is that Davis use a potentiometer (3-terminal voltage divider) whilst FO use a (2-terminal) variable resistance (which needs the addition of another resistor to make a voltage divider) for sensing the Wind Direction.  On the Weatherduino Transmitter PCB the variable resistance is connected to earth, with an additional resistance to the supply rail.  So there are two earth connections on the "RJ11" (4 contacts) part of the socket and the Davis plug must use another pin with an "RJ12" (6 contacts) connector for the supply voltage.  However, in the Fine Offset transmitters, the variable resistor is effectively connected to the supply rail, which could also be done with the Weatherduino transmitter (it's just necessary for the software to subtract the ADC value from 1023).

This could give several advantages; firstly the Davis and FO could use the same (4) pins with an RJ11 (4c) plug.  Also, there is an alternative version of the FO Wind Vane which appears to use Hall (semiconductor) switches instead of the 8 magnetic Reed switches.  I've never been able to test one, but it possibly NEEDS a positive voltage supply on the cable, in the same way that the Davis potentiometer needs both supply and ground connections (shared with the anemometer switch).  Similarly, the more recent Davis Anemometers now need both supply and ground rails to feed their Hall switch.

Cheers,  Alan.