This week my main task is debugging the audio signal quality.
I have plotted the audio data sampled by the ADC, with no audio or sine wave audio. It turns out that we have a larger than acceptable noise which is constantly affecting the signal.
(y axis: ADC readings, 3.3V corresponds to 32767 (uint16 max))
With some probing in the lab and with the new pre-amp, Adam confirms in the lab that the signal before the ADC has only a little noise introduced. So I focus on checking sampling errors or Bluetooth transmission errors in the digital domain, since that is where most of the noise is introduced. I am setting up a program to stream the ADC sampled audio onto the I2S bus on my stm32 discovery board, so that I can directly hear it through the on board DAC; in this way I can isolate whether the ADC or the BT module is faulting. This is what I will report on next week.
I have also updated the software diagram, and performed the quantitative tests for ADC sampling, signal latency, and BT range that we will present in our final presentation.
(Noooo! Most of my time I am exhausted in the sea of 3~4 circuit boards and jumper connections and I feel I am growing succinct/lazy on status reports :O )