One great thing about Multiwii is, you can connect it to your computer, or Android phone/tablet via Bluetooth! It means you can adjust PID and other settings via the wireless Bluetooth connection, and there is no USB connection required. However the Bluetooth module might require some change of default settings (baud rate) beforehand.

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I have an Arduino bluetooth transceiver module lying around, so I decided to give it a try. It connected successfully, but the Android app prompted there is no data received. I realized the Serial connection baud rate of Multiwii by default is 115200, but the default baud rate of the Bluetooth module is at 9600. That means I would have to change the default baud rate on the BT module for it to work.

A couple of ways to do this, first way is using a ISP programmer to connect the BT module and use Hyperterminal on Windows to send AT commands. Second way is to use Arduino as the programmer, and its serial monitor to send AT commands.

I prefer the second way (using Arduino), because I don’t have an ISP programmer, so here I will describe how I did it.

Connecting Arduino with Bluetooth Module

WIRING

• BT Module GND — Arduino GND Pin
• BT Module VCC (5V) — Arduino 5V
• BT Module TX — Arduino Pin 10 (soft RX)
• BT Module RX — Arduino Pin11 (soft TX)
• BT Module Key (PIN 34) — Arduino Pin 9

Arduino Code

This Arduino code takes the AT commands from Serial Monitor and sends those commands to the BT module, then reads the output of the BT module and displays it on the Serial Monitor.

The Arduino communicates with the BT module using the SoftwareSerial ports while the Arduino communicates with the user via the Serial Monitor.

#include <SoftwareSerial.h> SoftwareSerial BTSerial(10, 11); // RX | TX void setup(){ pinMode(9, OUTPUT); // this pin will pull the BT Module pin 34 (key pin) HIGH to switch module to AT mode digitalWrite(9, HIGH); Serial.begin(9600); Serial.println("Enter AT commands:"); BTSerial.begin(9600); // your own BT Module default speed in AT command more } void loop(){ // Keep reading from BT Module and send to Arduino Serial Monitor if (BTSerial.available()) Serial.write(BTSerial.read()); // Keep reading from Arduino Serial Monitor and send to BT Module if (Serial.available()) BTSerial.write(Serial.read()); } 

After connected the components and uploaded the code, it’s time to test it. You can do a ping test by entering AT in the serial monitor. If communication is successful the BT module would return “OK”.

Changing Bluetooth Default Baud Rate

If we have passed the ping test above, we can now attempt to change the baud rate of the BT module.

The bluetooth module baud rates are set by an hexadecimal index from ‘1’ to ‘C’.
Indexes are: 1:1200, 2:2400, 3:4800, 4:9600, 5:19200, 6:38400, 7:57600, 8:115200, 9:230400, A:460800, B:921600, C:1382400

To set a default baud rate, enter this command

AT+BAUD<index>

For example for multiwii, we need 115200 as the BT baud rate, we would enter AT+BAUD8.

If successful you should be returned “OK” in the serial monitor.

More AT Command for HC06 (Linvor 1.5)

Set Bluetooth Device Name

Send: AT+NAME
Response: OK

Set Bluetooth PIN Code

Send: AT+PIN
Response: OK

Check Firmware Revision

Send: AT+VERSION
Response: Linvor1.5

Examples

AT
OK

AT+VERSION
Linvor1.5

AT+BAUD4
OK9600

AT+NAMEBlueBee
OKBlueBee

AT+PIN1234
OK1234