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How To Add Bluetooth to your MultiWiiCopter

For not much more than $10, a Bluetooth adaptor is  a cheap and easy way to get in-flight real time feedback from the onboard sensors and allows quick and easy modification to PID values via the MultiWiiConf software. Here's how to do it.

1. Buy a serial to bluetooth adaptor - "Serial Bluetooth RF Transceiver Module RS232 w/ Backplane Enable & State Pin". The one from goodluckbuy.com is simple and works fine with the Arduino. 

2. Connect the USB FTDI adaptor to the BT adaptor. I used my breadboard wiring leads to hook up the pins in the following order.

3. FTDI	BT
   VCC	VCC
   GND	GND
   TXO	RXD
   RXI	TXD

4. Connect the FTDI USB Adaptor to a PC. The BT adaptor should now be powered with a blinking red led. Before using it with an Arduino running muliwii software, the baud rate of the BT adaptor has to be changed to 115200 from the default 9600. Now this is the part that stumped me for ages and sent me off looking up forums, updating bluetooth stacks etc etc until I figured out what I was doing wrong. To configure the BT adaptor, you need it physically connected to the PC via the FTDI USB adaptor but you don't want to connect the PC to the BT adaptor .... yet. The BT adaptor can only be configured when it's in an un-connected state. In your "Bluetooth Places" you should be able to see the device (by default called "Linvor") but it should show "not connected") and the red light should be flashing on the BT adaptor.
5. I used Advanced Serial Port Terminal to connect to FTDI USB. The AT commands must be copy and pasted to send to the device because it constantly polls and if you can't type fast enough to complete a command before it reads it in.
6. Send the "AT" command. BT responds with "OK"
7. Send "AT+NAMEMultiWiiCopter" to change the default from Linvor.
8. Send "AT+BAUD8" to change the Baud rate to 115200.
9. Now connect to the Arduino as per the connections in the table above.
10. Run the MultiWiiConf software and choose the BT COM port. 
11. Now you can fly around and see the gyro and accelerometer inputs change while in flight!

I found a page with quite a lot of detailed information on the BT adaptor during my searches. While it's native language looks Chinese, the Google Chrome browser seems to do a pretty good job translating it.