Dear Experts,
Hi
I use the ADC channel of an ATXMEGA32A4U chip to capture audio data and send it via USB port to Computer,
The problem is that I see a periodic noise on it that I could not find what is the source of .
I disconnect the analog circuit from ADC pin and find that noise still exists,
Could you please tell me what is the source of this noise and how I can remove it.
Please listen to attached wave file.
But about the Xmega program:
1. Micro clock is set to 32MHz.
2. ADC is set to : Signed, 12 bit, right hand side, 200000 clk, Manual triggered, ADC_PIN1
3. a timer is set with frequncy of 8000 sps and in every interrupt a manual ADC capture is triggered and samples are put into a circular Queue,
Then by USB port, those data are sent to PC program.
ADC Init code:
#define MY_ADC ADCA
#define MY_ADC_CH ADC_CH0
static void adc_init(void)
{
struct adc_config adc_conf;
struct adc_channel_config adcch_conf;
memset(&adc_conf, 0, sizeof(struct adc_config));
memset(&adcch_conf, 0, sizeof(struct adc_channel_config));
adc_set_conversion_parameters(&adc_conf, ADC_SIGN_ON, ADC_RES_12,ADC_REF_VCC);
adc_set_conversion_trigger(&adc_conf, ADC_TRIG_MANUAL, 1, 0);
adc_set_clock_rate(&adc_conf, 200000UL);
adc_write_configuration(&MY_ADC, &adc_conf);
adcch_set_input(&adcch_conf, ADCCH_POS_PIN0, ADCCH_NEG_NONE, 1);
adcch_write_configuration(&MY_ADC, MY_ADC_CH, &adcch_conf);
}Interrupt routine to capture audio:
static void tc_callback(void)
{
int16_t result;
adc_start_conversion(&MY_ADC, MY_ADC_CH);
adc_wait_for_interrupt_flag(&MY_ADC, MY_ADC_CH);
result = adc_get_result(&MY_ADC, MY_ADC_CH);
if(result < 0)
{
result = 0;
}
result -= 0x0510;
result *= 16;
SendQ0[wsendidx]= result;
wsendidx++;
if( wsendidx >= QSIZE )
{
wsendidx = 0;
}
tc_clear_overflow(&TCC0);
}
Thanks for you kind help,
Mehrdad,
