Hello,
First of all, I am new to this forum, so sorry for possible vagueness and possible misleading AVR terms in my post, but I will try to do my best.
I am currently creating a device that would be able to detect the direction of incoming sound (sound source). This is just a part of final project, but I am stuck with this problem FOR DAYS....
I am using: Arduino Uno (ATMEGA328P), simple electret mics (~1, 5 cm), mic amps: LM358.
Since I am quite new at AVR, it took me awhile to figure out ways, how to read sound at fixed, and equal intervals using ISR (instead of using simple analogRead). I managed to setup registers and write code that was able to read data using only one mic. Below, I present my code (my description is below the code), which was modified a bit (code that is not important for this problem was removed).
#define SAMPLES_QTY 64 // Qty of samples to be picked from ADC.
#define TIMER_INT 64 // Timer 1 OCR. 64 cycles at 16Mhz -> 4us.
#define CHANNELS 3 // Mic number.
volatile uint8_t adcMSB = 0;
volatile uint8_t adcLSB = 0;
volatile uint16_t acqSamples[CHANNELS];
volatile bool readCompleted;
double realData[CHANNELS][SAMPLES_QTY];
double imagData[CHANNELS][SAMPLES_QTY];
void setup()
{
Serial.begin(115200);
doSetup();
}
void loop()
{
readData();
//dummy loop
for (int j = 0; j < SAMPLES_QTY; j++) {
Serial.print((int)realData[0][j]);
Serial.println(" ");
}
}
void readData() {
for (int i = 0; i < CHANNELS; i++) {
acqSamples[i] = 0;
for (int j = 0; j < SAMPLES_QTY; j++) {
realData[i][j] = 0;
imagData[i][j] = 0;
}
}
readCompleted = false;
uint8_t originalTIMSK0 = TIMSK0; // Recording Timer0 Mask;
TIMSK0 = 0x00; // Disable Timer0.
TCNT1 = 0;
//now_time = micros();
TIMSK1 |= (1 << OCIE1B);
while (!readCompleted) {};
TIMSK1 &= ~(1 << OCIE1B);
//dur = micros() - now_time;
TIMSK0 = originalTIMSK0; // Enable back Timer0.
}
void doSetup() {
// Setup Timer 1
cli();
TCCR1A = 0x00;
TCCR1B = 0x00;
TCCR1C = 0x00;
TIFR1 = 0x00; // Timer/Counter Int. Flag Register. to enable Out. Comp. A Match Flag: TIFR1 |= (1 << OCF1B);
TCCR1A = ((0 << COM1A1) | (0 << COM1A0) | // OFF. Compare Match Output, Timer 1, A1:A0 (control of OC1A pin).
(0 << COM1B0) | (0 << COM1B1) | // OFF. Compare Match Output, Timer 1, B1:B0 (control of OC1B pin).
(0 << WGM11) | (0 << WGM10)); // Waveform Generation Mode, Timer 1, 0:1. Mode: CTC; TOP: OCRA.
TCCR1B = ((0 << ICNC1) | // Input Capture Noise Canceler, Timer 1, (used by ICP pin).
(0 << ICES1) | // Input Capture Edge Select, Timer 1, (used by ICP pin).
(0 << WGM13) | // Waveform Generation Mode, Timer 1, Mode: CTC; TOP: OCRA.
(1 << WGM12) | // Waveform Generation Mode, Timer 1, Mode: CTC; TOP: OCRA.
(0 << CS12) | (0 << CS11) | (1 << CS10)); // Clock Select. Arduino UNO 16Mhz / 1 = 16 Mhz.
TIMSK1 = 0x00; // Out. Comp. Match Int. to enable Out. Comp. Match A Int.: TIMSK1 |= (1 << OCIE1B);
TCNT1 = 0x00; // Timer/Counter.
OCR1A = TIMER_INT; // Output Compare Value.
OCR1B = TIMER_INT - 2;
// Setup ADC
ADMUX = 0x00;
ADCSRA = 0x00;
ADCSRB = 0x00;
ADMUX = ((1 << REFS0) | // Setting reference voltage (Vcc).
(0 << ADLAR) | // ADC right adjust (for ADCL and ADCH).
(0 << MUX3) | (0 << MUX2) | (0 << MUX1) | (0 << MUX0)); // Analog channel select: ADC0.
ADCSRA = ((1 << ADEN) | // Enable ADC.
(1 << ADATE) | // Auto Trigger enable.
(1 << ADIE) | // ADC Interrupt enable.
(1 << ADPS2) | (0 << ADPS1) | (1 << ADPS0)); // Setting prescaler 32 -> 500Khz ADC clock -> Fs = 38461Hz -> T = 26us.
ADCSRB |= ((1 << ADTS2) | (0 << ADTS1) | (1 << ADTS0)); // ADC auto trigger source selection -> Timer 1 Compare Match B selected.
DIDR0 = 0x00; // Turn Off Digital Input Buffer.
sei();
}
ISR(TIMER1_COMPB_vect) {
// Invoked on OCR (CTC).
}
ISR(ADC_vect) {
// If the result is left adjusted (ADLAR) and no more than 8-bit precision is required, it is sufficient to read ADCH,
// otherwise, ADCL mus be read first, then ADCH.
if (!((acqSamples[0] == SAMPLES_QTY) && (acqSamples[1] == SAMPLES_QTY) && (acqSamples[2] == SAMPLES_QTY))) {
adcLSB = ADCL;
adcMSB = ADCH;
switch (ADMUX) {
case 0x40: // ADC0
realData[0][acqSamples[0]] = ((adcMSB << 8) | (adcLSB & 0xff)) - 327;
acqSamples[0] += 1;
ADMUX = 0x41;
break;
case 0x41: // ADC1
realData[1][acqSamples[1]] = ((adcMSB << 8) | (adcLSB & 0xff)) - 327;
acqSamples[1] += 1;
ADMUX = 0x42;
break;
case 0x42: // ADC2
realData[2][acqSamples[2]] = ((adcMSB << 8) | (adcLSB & 0xff)) - 327;
acqSamples[2] += 1;
ADMUX = 0x40;
break;
}
} else readCompleted = true;
}
IMPORTANT: I know that assigning zero bit values is useless, but I did that on purpose, because that is clearer to me. Moreover, some code comments might be incorrect, because I might have made some adjustments and forgot to update comments…
I have chosen to use ADC Auto Trigger (ADATE = 1) mode that will be attached to Timer 1 compare match B event. I have chosen CTC mode for my Timer 1, I have also selected a pre-scaler of 1, so that means I am keeping clock speed at 16Mhz. Since CTC mode compares only OCR1A value and Auto Trigger mode is attached to B event, I set OCR1B to a less value (i.e. -2). I am not quite sure whether that is mandatory, because sometimes I could not feel any difference... Then I setup ADC. I setup reference voltage (Vcc), then I select initial ADC0 port (which is not, obviously mandatory since I cleared all values of this register just above). Then I enable ADC, switch Auto-Trigger mode on, enable ADC interrupt, setting pre-scaler to 500Khz, which should provide me with ~38461 sampling rage (500k/13) [when there is only one mic of course]. Finally I switch off digital filters (I found that as a good habit in such cases) and turn on global interrupts again.
So that's how I understand it “should” work from my POV: every time Timer1 compare match B event occurs, ADC conversion starts, while it is happening, Timer1 compare match B event will occur (my TIMER_INT is equal to 64 so that leads to a period of 4us while my sampling frequency is just 26us) and ADC will just ignore this event and carry on its conversion. After ADC finishes current conversion, ADC ISR is executed. ADC ISR is supposed to be handing multiple channels, so there, I read ADCL and ADCH values, compare, check WHAT channel is currently active, assign data to array and switch to another ADC channel. I do that for three channels and ADC conversion is stopped, when 64 samples are taken for each array/channel.
HOWEVER, that does not work properly. Although each mic is assigned to a corresponding ADCx channel, it seems, that the order and data is totally ruined. For example, when I switch my first mic into ADC0 channel (others are pulled out completely), read ADC0 data (I play 2khz sound very close to the mic), loop it out realData[0], and I see that it looks like being good. When I switch the same mic into ADC1 channel (other are still out), read data, and loop the data of realData[1], it looks like good, BUT.. BUT, when I decide to loop out the data of ADC0 channel (realData[0]) (my mic is still attached to ADC1), IT DOES SHOW SIMILAR DATA TO realData[1], which is total non-sense… and therefore I cannot figure out the order of my mics and my thing does not work. Looks like data is totally ruined and incorrect... I do not know what is wrong here: Does my code have silly bugs? Is this ADC conversion approach for multiple channels correct? Do I read it properly? Is there a simpler way of doing this?
Guys, it just drives me crazy.. 
just a week ago, I knew nothing about AVR registers, internal functionality etc. and I really pushed myself forward, but these things are new to me, so I migh have understood quite a few things not in a way as I was supposed to.
THANKS for your help and patience.