It looked simple enough from the start – but there are many caveats with the HC-06 BT module. First of all the one I had needed 3.3v rather than 5v. The Rx line needed a voltage divider – so it was not only to plug in directly. Then the trickiest part was to determine the Baud rate while testing the AT command. Different places gave different numbers, but it turned out to be 9600 Baud in the end. The other tricky thing was to enter AT mode – for some reason it only works in the beginning of the HC-06 boot-up cycle – within approximately 2s. Thus trying to send AT commands after that proved to be tough.