It's far too late at night to be writing this, so I apologise in advance for the rambling nature of this post.
One of the key things to know while sailing, funnily enough, is the state of the wind: direction and speed. On smaller cruising yachts this is usually done with masthead mounted equipment, either wired or relying on simply looking at it in the case of some weathervanes. The hassle of retrofitting such a system through a 20-30ft mast puts the vast majority of people off, and sometimes involves taking the mast down completely, a lengthy and costly process.
There are some wireless systems out there, but the price is incredible for something which could be done far cheaper using an Arduino.
This idea's just something I've been playing around with for a bit, but by sending the pulses from a non-detented rotary encoder via an Xbee to the Arduino base station it would be child's play to determine wind direction, wind speed is another issue though, suggestions are welcome, possibly involving a thermal flow meter of some sort.
My main issue though, is how to interface the mast mounted sensors with the Xbee module: whether the module is capable of sending this data without an additional Arduino.
Yet again, apologies for lack of clarity here, feel free to grill me about this all :
This sounds feasible, but surely you'll need to supply power to the sensor/Arduino at the top of the mast? Will you use batteries? Or is there a ready-made power supply already up there?
Power will be an issue I think; there's power for the navigation lights up there, but I'd rather make it a stand-alone system to make for easier installation.
Over on the Sparkfun forums someone suggested a simple wind turbine to charge the batteries, I'll look into this. Also I plan to only transmit every half second instead of more often, hopefully this will require less power.
Any other suggestions for the power problem would be more than welcome, although the size is an issue, no huge solar panels :
A pot built for position-sensing applications or magnetic pot is probably the best choice -- you need absolute position and those will give it. That's about $30 or so for a mag pot.
If you get clever with the power, a small solar panel plus a substantial battery should do for a recreational sailboat that is not cruised extensively.
Also I plan to only transmit every half second instead of more often
Isn't this a bit frequent for wind direction and speed?
I assume, if the wind changes appreciably, it will be you taking some action. If that's the case, it seems like an average speed and direction would be more useful.
But the above post does mention a "sleep" mode. Maybe do not transmit periodically -- only transmit when the wind spd & direction changes appreciably. Of course if you do this, a missed transmission would mean bad data.
I've been looking into the CYRF7936 which uses half the current during operation and sleeps at 1uA. But I haven't built a prototype or anything yet.
Also I plan to only transmit every half second instead of more often
Isn't this a bit frequent for wind direction and speed?
I just picked half a second out of the blue, it would probably make much more sense to update when it changes by over a set value.
I've been doing some research as well, and it seems that marine navigation units and sensors adhere to NMEA 0813 to communicate. Would it be feasible to transmit in NMEA format for compatibility with other systems on the yacht?
In other news, I got the Freeduino from NKC Electronics through today, great little kit, but I'm having trouble uploading a simple sketch to it. I've loaded the Blink sketch in the IDE, but when I try to upload to the board, the editor screen goes white and freezes and the TX and RX LEDs on the board blink rapidly until unplugged. I've left it for an hour and still come back to nothing. Any ideas?
I've been doing some research as well, and it seems that marine navigation units and sensors adhere to NMEA 0813 to communicate. Would it be feasible to transmit in NMEA format for compatibility with other systems on the yacht?
While I cannot directly answer your question, I did notice some NMEA messages on the Parallax forums. If you don't get a definitive answer here, it seems likely that you would get one there.
This sounds like an interesting project. However, I ask you since it greatly effects your transmission scheme etc., what device are you going to use to display the info from the masthead unit?
Most wind systems on the market use a proprietary format between the masthead unit and the main control box. How they transmit to the display unit is another question. Some use NMEA, some use a highly bastardized form of NMEA, and others use a proprietary format. Best to decide on what display head you will use before deciding how you want to do this...
I like the idea though! Why could you not use continuous pots for both the wind direction section and the wind speed? I don't know what the life is on the pots though... 10MM cycles might be a problem. Most commercial units use a jewel bearing and a hall effect sensor to count rotations of the wind-cups. You might be able to hack some cheap anemometer unit like this one: http://www.partshelf.com/la-crosse-tx15u.html
or http://www.digitalkitchenstore.com/tx23u.html
or http://www.partshelf.com/ub-wgr968.html
The last one even has a 915MHz transmitter & solar cell unit. Only theirs is only designed to update the info every minute, so you would definitely need to hack...
