Local Communication Link

Once the basic navionics package was assembled it became clear that we'll need some means of real-time monitoring of the system for tuning the command-and-control algorithms of the boat. The primary satellite link has a fairly steep cost factor associated with it and the SBD channel has an inherent delay which makes it impractical for real-time feedback and control. In order to maintain two-way real-time communication with the boat during development and testing (short of chasing the prototype in the pool with a laptop and USB cable :) we decided on a low-power radio link. This piece will evolve once boat moves on to large-scale testing as Bluetooth has limited range but for now it provides an easy way for communication with any BT enabled host device. 

• Current selection: JY-MCU Bluetooth Serial Port
• Status: Temporary / Stage solution
  
  
• Criteria: Convenience, compatibility, power consumption, cost 
• Finalists: JY-MCU Bluetooth, SainSmart Bluetooth XBee Shield, Pair of generic NRF24L01+ 2.4GHz transceivers
• Main decision factors: Availability, cost, ease of integration

 (click image for larger view) 

Spec highlights:

• 1.73 in x 0.63 in x 0.28 in (4.4 cm x 1.6 cm x 0.7 cm)
• 0.25 oz (7 g)
• Emulates standard COM port

Caveats:

• Limited range suitable for close-range monitoring and control;
• As the project evolves, we will be switching to the Nordic 2.4GHz transceivers. Those will require a separate host micro-controller on the PC/Tablet side to interact with, which makes the setup a bit heavier;