I have been working for a while with a HC06 bluetooth module along with an Atmega 168A microcontroller and everything was fine until a day ago when the bluetooth transmission just went off. Data is being sent along with the correct protocol and I discovered that transmission ocurred only when I place a finger between the TXD and RXD pins of the module. I have tried to vary pull up resistors, baud rate and capacitors between VCC and GND but only the finger trick seems to work. What could be the problem?
The "finger trick" looks to me like a symptom of an unconnected pin. Unconnected pins in MOS circuits can be very high-impedance, and the resistance (and capacitance) of a finger can affect operation. I'd check very carefully for pins/connections that have become disconnected. The break in the circuit could be a breadboard pin, a connector pin, or even a cracked solder joint on the Bluetooth module itself. If the module has suffered a mechanical impact, also check for completely missing surface-mount components.