AAR-04 and ARX-BT3: Bluetooth serial connection fails after power on


I already asked this question in the Arexx forum, but without any reaction.

I have successfully used the AAR ROBOT Android application and the corresponding Arduino sketch to control the robot.

After that I used a serial echo test program, and I connected successfully with Putty over Bluetooth to the robot. I also modified an Android application to communicate with Firmata messages between a mobile phone and the AAR robot.

The problem I have is that this only works once directly after uploading the sketch to the Arduino over the USB cable. I can then unplug the USB cable, connect via Bluetooth from the PC or the mobile phone, and the Bluetooth serial connection works as expected. But when I power off the robot and power it back on, the Bluetooth connection does not work. I can connect to the ARX-BT3 module successfully (blinking on the module stops), but nothing is received on the robot's board itself. The LED for serial transmit on the robot board does not blink if I send something from Putty or from the mobile phone. When I use the Firmata sketch, I can see the initial blinking that indicates that the Firmata code has been initialized, so the sketch is indeed loaded.

What can be the reason that the serial connection over Bluetooth works directly after uploading the sketch, but not after the sketch is loader after a power-on? If anybody could explain this behavior and suggest a solution I would be most grateful.

Thanks Stephan

Problem solved after a hint that it could be related to the batteries. With freshly charged batteries the Bluetooth connection works after a power-on without a previous connection via USB.