A very small signal from a sensor is amplified through a series of analog amplifiers. The final signal is an audio signal which is sampled by a microcontroller. This signal is then sent digitially over i) a USB line audio connection to a PC, ii) to the BC127 module, which transmits is wirelessly to a PC.
When operating with the BC127 Bluetooth module, there is alot of noise in the audio (the system work fine in the ‘USB’ mode). The module has its own 3.3V regulator and sufficient decoupling capacitors. The entire system operates off a 3.7V li-ion battery. The noise fluctuates when parts of the circuit are touched or moved around.
Is there a way to get rid of such noise and what could be the root cause of it?