Having successfully installed a SiK radio, I decided to try connecting a BT module to perform the basic function of modifying Ardupilot parameters using my Android phone.
My first mistake was to buy a BLE (low energy) module. After some frustrating time, I concluded that this was not going to work which was confirmed by a fellow RCG member. Fortunately I was able to get a refund from Amazon and then purchased a HC-05 "classic bluetooth" module.
First step was to confirm the wiring between the BT module and the F405. I am using the S5 UART so:
5v to 5v
Ground to ground
T5 to BT RX
R5 to BT TX
Since the default baud rate of the HC-05 is 9600 baud, I preset the Ardupilot parameters:
SERIAL5_BAUD 9 (9600)
SERIAL5_PROTOCOL 1 (MAVLINK1)
N. B. The serial ports require power from the battery, not USB.
I use Qgroundcontrol to modify parameters via my Android phone. In order to do this via BT, I first paired the module via Android Bluetooth settings. The HC-05 PIN is 1234 by default.
In Qgroundcontrol, it is necessary to add a new "Comm Link" which can be found in the "Q" menu. It is only necessary to set the Type to Bluetooth. The name can be changed if desired. The device should be found by selecting "Scan" and selecting the HC-05 which will then populate the Bluetooth link settings.
Returning to the "Comm Links" page, it is now possible to select the HC-05 device and Connect.
Switching to the main Qgroundcontrol screen will show the vehicle connection has been made and the parameters from the flight controller being downloaded. Full functionality of the ground station is then available via BT with a range of 20+ metres.