I have an expansion board by ST mounting an analog mic (MP23ABS1). The mic out pin (via a diff. amplifier) is given on a connector. I take that signal and feed it to the AIN5 (P0.29) on nrf52810. I want to continuously sample the analog mic data at 8000Hz and store the data in a buffer and transmit that over BLE. I've implemented a solution but I'm not getting the right values (already tested analog signal independently over oscilloscope). What I have done is, I initialized the ADC and the configured the channel with default values in single ended mode. Created an application timer with repeat mode and period of timer as 0.125ms(1/8000Hz) and in the timer callback function I sample the ADC(nrf_drv_saadc_sample()). After buffer (96 bytes of int16_t) is full, I check for NRFX_SAADC_EVT_DONE and convert the buffer, in the saadc handler. And this process repeats after every 0.125ms.
The issue is that the buffer is filled with starting 4-5 bytes as 0x0000 and some random values in between as 0x0000 which get filled gradually. Also the digital values don't change much with changes in the sound I make (while I check in the buffer in the debug mode). Can you help me identify where I am going wrong with the implementation ?
Init Routine:
bool SDL_Mic_Init(void)
{
uint32_t ret_code=false;
ret_code=nrf_drv_saadc_init(NULL, mic_callback); //ADC Initialization
if(ret_code==NRFX_SUCCESS)
{
nrf_saadc_channel_config_t adc_channel=NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(MIC_INPUT_DATA_PIN);
ret_code=nrf_drv_saadc_channel_init(MIC_ADC_CHANNEL,&adc_channel);
if(ret_code==NRFX_SUCCESS)
ret_code=true;
app_timer_create(&test_timer,APP_TIMER_MODE_REPEATED,sampling_callback);
nrf_saadc_continuous_mode_enable(2000); //for 8K sample rate (16000000/2000=8000Hz)
}
return ret_code;
}
When I send a start streaming command from app
bool Mic_DataAcq_Start(void)
{
uint32_t ret_code=false;
//Set the buffer in RAM that will acquire adc data(raw datamic)
ret_code=nrf_drv_saadc_buffer_convert(mic_handler.audio_sample , AUDIO_SAMPLES_BUFFER_SIZE);
if(ret_code==NRFX_SUCCESS)
{
ret_code=true;
}
app_timer_start(test_timer, ticks, NULL); //ticks=APP_TIMER_TICKS(0.125)
return ret_code;
}
After 0.125ms, timer handler will call nrf_drv_saadc_sample() and after buffer is full the following will be calledvoid mic_callback(const nrf_drv_saadc_evt_t * p_event)
{
if(p_event->type==NRFX_SAADC_EVT_DONE)
{
//copy mic_handler.audio_samples buffer into a copy buffer
// memcpy(SRV_DATA_state.txLogFrame3.txStreamFrame.mic_rawaudio.audio_raw_val, mic_handler.audio_sample, AUDIO_SAMPLES_BUFFER_SIZE);
//Set a flag to indicate FSM process that data is ready to be sent over BLE
//MSG_SetFlag(MSG_TYPE_SRV_DATA, DATA_FLAG_AMIC_DATA);
nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer , AUDIO_SAMPLES_BUFFER_SIZE);
}
}
