I wrote this code a little while back and have found it quite useful for sampling at defined sampling frequencies. It over samples to get 12 bit values from the 10 bit ADC. The basics of oversampling is that for every n bits you want to add you have to sample at 2^(2*n) times the desired sampling frequency. So, if you want to get 12-bit data from a 10 bit adc at 10Hz you would have to sample 2^4 = 16 times faster (160Hz). This is exactly what this code does for you. To initialize you must first declare the analog pin as an input as you would do normally, then call the setupADC() function. If you wanted to sample channel 2 at 40Hz (actually sampling at 640Hz) you would declare A2 as an input and then call: setupADC(2,40). Then you can do what ever you please with the data by changing the code after the comment "DEAL WITH DATA HERE" in the adc interrupt service routine. The code below is setup to simply output the data over a serial port connection every time the oversample buffer fills. This is all interrupt driven so you main loop is open to do whatever in between sampling events.
/*
#define BUFFER_SIZE 16 // For 12 Bit ADC data
volatile uint32_t result[BUFFER_SIZE];
volatile int i = 0;
volatile uint32_t sum=0;
ADC and Timer1 setup function
Argument 1: uint8_t channel must be between 0 and 7
Argument 2: int frequency must be integer from 1 to 600
WARNING! Any value above 600 is likely to result in a loss
of data and could result in a reduced accuracy of ADC
conversions
*/
void setupADC(uint8_t channel, int frequency)
{
cli();
ADMUX = channel | _BV(REFS0);
ADCSRA |= _BV(ADPS2) | _BV(ADPS1) | _BV(ADPS0) | _BV(ADATE) | _BV(ADIE);
ADCSRB |= _BV(ADTS2) | _BV(ADTS0); //Compare Match B on counter 1
TCCR1A = _BV(COM1B1);
TCCR1B = _BV(CS11)| _BV(CS10) | _BV(WGM12);
uint32_t clock = 250000;
uint16_t counts = clock/(BUFFER_SIZE*frequency);
OCR1B = counts;
TIMSK1 = _BV(OCIE1B);
ADCSRA |= _BV(ADEN) | _BV(ADSC);
sei();
}
ISR(ADC_vect)
{
result[i] = ADC;
i=++i&(BUFFER_SIZE-1);
for(int j=0;j<BUFFER_SIZE;j++)
{
sum+=result[j];
}
if(i==0)
{
/****DEAL WITH DATA HERE*****/
sum = sum>>2;
Serial.println(sum,DEC);
}
sum=0;
TCNT1=0;
}
ISR(TIMER1_COMPB_vect)
{
}
