The Roving Networks RN-41 was chosen to implement the Bluetooth interface for the VI because:
The only major design impact of the RN-41 is that it requires a large “keepout” area near the antenna of the module. In this area, there should be a minimal amount of traces or copper blocking the radio signal. The RN-41 Datasheet illustrates the suggested keepout zone on page 9. Otherwise, the RN-41 is controlled with a serial UART bus with similar bitrates to the CAN data (230kbps
In our testing we discovered that hardware flow control is necessary to fully saturate the bluetooth link. The firmware on the RN-41 does not respond well to buffer overruns - if data is written to the RN-41 faster than it can be sent over the bluetooth link, the module will eventually overflow and reset without warning. Adding the RTS and CTS lines to UART1 on the LPC1769 fixed this problem
The tradeoff of a simplified Bluetooth module is that the implementation details of the SPP profile limit the throughput of the bluetooth link. While the underlying Enhanced Data Rate (EDR) bluetooth link can technically operate at 3Mbps, the asynchronous nature of SPP limits the RN-41 to 240kbps in slave mode. In our testing, the RN-41 only hit this speed for brief peak bursts. The sustained average speed was 202kbps. Future designs may consider using a more complicated Bluetooth chipset with an HCI interface implemented on the MCU for greater throughput. An example of a test run:
VI Reference Design