Bluetooth serial instead of USB serial

Hi. I have an Arduino Duemilanove with Atmega328 and would like to use a bluetooth connection to replace the default USB connection. I need this for both uploading sketches and serial communication.

So I have 2 problems: How do I connect the board to a serial plug, and then where will a find a cheap bluetooth serial convertor?

If I want to connect the board to a serial 25pin D-sub, do I just connect: - d-sub pin 7 to arduino gnd - d-sub pin 2 to arduino pin 0 - d-sub pin 3 to arduino pin 1 or is it not that simple?

And now to begin my search for a cheap bluetooth serial convertor. It would help if I knew what these things are actually called so that I can google for them :)


Hi tpot,

there is already an Arduino with bluetooth interface called Arduino-BT which does exactly what you want. It is not cheap, but I don't think your own solution will be cheaper. Have a look at its curcuit in the hardware section:

The serial interface of the ATmega requires TTL level signals (0V and +5V). Some bluetooth chips use 3.3V signals with 5V tolerant inputs (e.g. WT-11) which is also ok.

You cannot directly connect a 25pin/9pin RS-232 cable to the ATmega because the RS-232 signal levels are around -12V and +12V which will fry your Arduino inputs. A MAX232 chip is needed for level conversion.


Thanks Mike T.

I've had a read about the Arduino-BT but it doesn't quite do what I want. I need to program an Atmega328 and remove it from the board. So it looks like I need a bolt-on BT solution after all.

Hi tpot,

some others were working on a bluetooth shield:

Many people are using Xbee as wireless communication (, I never tried it.

The problems is always that bluetooth modules are expensive. You can find some examples of modules here:

You should also read the comments on those product pages because it is not easy to get them running.

Using wireless connections for loading new sketches has always been a problem because you need to reset the ATmega just before starting the download. With the USB and serial connections, the DTR handshake line is used for the reset (refered as Auto-Reset). When you search the forum, you will find many problems.

I modified my Arduino-BT to make use of the Auto-Reset feature ( which solved my upload problems. Modifying the hardware is not enough, you also have to change the bootloader.