Jan 15, 2012

Arduino Bluetooth Link


In a previous Arduino project, I used the BlueSmirf Bluetooth Breakout Board to communicate with my Android phone. There was absolutely no special code on the Arduino to handle Bluetooth since, by default, the BlueSmirf is set as Slave and will accept any connection call. The phone app was doing all the work.

The next logical step was to use the BlueSmirf interface by programming the Arduino. Using a second Bluetooth board, I decided to create a link between two autonomous Arduinos. To make things interesting, I've set a couple of rules for the project. I wanted to heave the same code on both Arduinos and have the whole connection process be automatic. I also wanted the Master device to scan for other devices, retrieve the MAC address, connect and send data.  Here's the video of the final result:



My biggest issue started with the Sparkfun proto shield for Arduino. It has a built-in socket for their Bluesmirf device. Nice marketing move! This socket is hardwired to use the Arduino pins 0 and 1 for communications. It all looks good until you need to use it in the real world. Here are the pros and cons:

Pros:

  • No wiring needed to connect the Bluesmirf board.
  • No extra library needed to do serial communications.

Cons:

  • You must remove the Bluesmirf breakout board every time you need to plug the Arduino board in the computer. Why? Because of the hardwired Bluesmirf socket the Arduino board communications are mixed with the Bluesmirf interface.
  • Another consequence of the previous problem: You can't used the USB serial output to the computer to send debug info. That is really annoying when debugging your project.
  • The power is always ON for the Bluesmirf.

I'll fix this by using different pins for the Bluetooth communication using the NewSoftSerial library. I will also modify the Sparkfun Bluesmirf socket to use any communication pins and to have control on the power usage.

For more details continue reading after the break. (Warning! Geeky stuff about code and electronics)




Tips about BlueSmirf interface
  1. Read the User Manual
  2. Serial speed: By default, BlueSmirf is set to 115200 so you need to call Serial.begin(115200); before sending the first command.
  3. The “$$$” command is the only one that is not followed by a carriage return. Why? To complicate things of course. Use print() for the “$$$” command and println() for all other commands.
  4. Read and validate all the responses that are sent back.
  5. Wait 100ms delay after each command you send and before trying to read the response. This will give Bluesmirf the time to process the command.
  6. Don't forget to exit the command mode (using “---”). Some commands are not effective until you have exited the command mode (e.g. SM command).

A simple test
A quick way to get two Arduino+Bluesmirf connected is by hard-coding the Slave's MAC address into the Master connection command. With this there's no need for code in the loop() function. In the following example, the MAC address of the Slave Bluesmirf is 000666123ABC. The example also assumes that the RX and TX are connected to pins 0 and 1. Here's the code for both Master ans Slave:

To test, start the Slave 5 seconds before the Master. The 'Connect' lights on both Bluesmirfs will turn green when the connection is open.

Instructable
After many questions about this project, I finally decided to make an Instructables about it.