Doing a whole lot inside an interrupt is usually a bad idea. I'd suggest setting a flag in the interrupt, and testing the flag in loop(). There are more sophisticated approaches, adding a "job" to a queue, but setting a flag should be fine for this.

What happens if you reverse the wires? That is, wire X to a1 and Y to a0?

Possible but not easy.

Can the person be wearing some sort of beacon. Say rfid or an xbee. You can then triangulate using multiple stations.

If no beacon, how about pressure sensors under the floor tiles.

Otherwise, you might need to do object detection using vision processing.  I think the CMU cams can do this. Not sure though. This is moderately difficult.

Give it a shot, but if it doesn't work don't get frustrated and give up on arduino. Try another, but simpler, project.

1. What do you mean by "bugging out"
2. By "separate sources" do you mean separate power supplies? Are the grounds connected?
3. You might want to use an hbridge rather than relays

In nmea.h, after including WConstans.h, add
#undef abs
#undef random

wiring.h redefines some macros defined in standard c/c++ headers. When the "real" definitions are parsed, it barfs. The #undfines "fix" it.

Check out http://ladyada.net/make/xbee/arduino.html. Basically, you need to reset when the upload starts. You need the connect DTR to a digital I/O on the transmitter, configure the transmitter to forward the digital I/O to the receiver, then connect the digital I/O on the receiver to reset. The xbee won't provide enough current to reset, so you'll need to use a transistor to bump the current.

If I recall correctly, avrdude can be configured for multiple protocols. I suspect that what you need to do is: 1) add your protocol to the avrdude program and 2) edit the config file to add your protocol. I think arduino has its own copy of avrdude, so getting your changes accepted by the arduino folks may not be as hard as getting them accepted by the avrdude folks.

NOTE: To be very clear, "If I recall correctly ...". This is based on a 2-3 month old recollection of a quick peek at the avrdude code ... I'm likely lying through my teeth ;->

It would be very simple. Change LibraryManager's "private File libDir" to "private File[] libDirs". Then in refreshLibraries walk all the libDirs rather than the single libDir.

I've added the following requests to http://www.arduino.cc/playground/Main/SuggestionsBugs:

1) Look for "user" libraries in the folder "libraries" that is a sibling of sketch folder. That is, if the current sketch is ~/arduino/robot/robot.pde, look in ~/arduino/libraries for libraries. So, #include "pid.h" will find pid.h in ~/arduino/libraries/pid/pid.h. It's a pain when I copy my sketches and libraries from machine to machine, or try to give them to friends or classes, that I have to install them into <ARDUINO>/hardware/libraries. It's an easy change. If given the "go-ahead" I'd be glad to do it myself.

2) Libary path. Add a property for library path, so I can have libraries somewhere besides <ARDUINO>/hardware/libraries. It's an easy change. If given the "go-ahead" I'd be glad to do it myself.

I've added the following request to http://www.arduino.cc/playground/Main/SuggestionsBugs:

Per sketch properties. When opening SKETCH.pde, add the properties from SKETCH.properties. It's an easy change. If given the "go-ahead" I'd be glad to do it myself.

The arduino must be reset just before uploading the program. You need to get the bluesmirf's DTR or RTS signal connected to the arduino RESET. I believe that Lady Ada has some info on doing this. Not sure if it was for bluetooth or an XBee.

What's the library? Can you post a link? If you can I'll take a look and might be able to tell you what to do next.

Try to get it working on the Arduino. If it doesn't, try a Sanguino. sanguino.cc. It's basically an arduino that uses an atmega 644p, which has 64k of flash and 4k of RAM. At least I think its 4K, not sure off the top of my head.

Thanks! I'll try it later tonight. Their stuff is windows only, but their site turned up the right thing for me to look for: RFC2217.

There are several "proxies" out there, including the "Serial Proxy" at the bottom of the arduino Software page, that are really bridges. They monitor a serial port and a TCP port and whatever they read on one they send to the other.

I want something slightly different: a device driver that looks like a serial port, but rather than connecting to a piece of hardware is a proxy for a telnet session. Opening the port will initiate the session. Closing it will end the session. Need some sort of stty interface to set the remote IP:PORT on *nix. Something equivalent for Windows.

"Why do you want this?", you ask. I've got one of lady ada's ethernet shields. This shield looks like a serial port to the arduino, including DTR. By connecting the XPORT DTR to arduino RESET, I think I can remotely upload programs to the arduino.