Boat project: Autopilot remote and MOB FOB

Lots of people are sailing around with Autohelm autopilots, for which no wireless remotes are available (to my knowledge anyway).

Hobby sites like sparkfun.com and lipoly.de sells a wireless fob for the 2.4 GHz band that fits the bill nicely with 5 buttons and a programmable Atmel ATtiny 24 on board. On the receiver end, another Avr talks to the receiver radio and the Seatalk bus.

The 5 available buttons may be laid out like:

• Left: Port 1 degree
• Mid + Left or Up: Port 10 degrees.
• Right: Starboard 1 degree
• Mid + Right or Down: Stb. 10 degrees.
• 2 Mid presses followed by left/right within 3 secs: Tack 100 degrees.
  This will be given as 10x10 degree commands on the bus to suit all pilot types.
• The receiver Avr will listen on a uart for GPS XTE (Cross track error) NMEA commands.
• A switch will determine whether these should be used for driving the autopilot from the active route in the GPS.

In addition the remotes can be used as MOB FOB's:

• The att24's watchdog is used to wakeup the uC and send a keepalive message every 30 secs.
• If the signal does not arrive (because the FOB drowned by going overboard) the receiver will issue an alarm as for the AIS SART.
• Some kind of procedure for signing the FOB's in and out needs to be devised. ??
  Maybe provide a USB socket (In AVR Firmware) (com port) and and a windows app?
• When reproprogramming the att24 in the FOB, a serial number must be flashed in.