First i bring a simple sample code on an analog to digital conversion
#include <avr/io.h> int ADC_Read; //Variable used to store the value read from the ADC converter #define PB5 5 int main(void){ DDRB |= (1<<PB5); ///PB5/digital 13 is an output ADCSRA |= ((1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0)); //Prescaler at 128 so we have an 125Khz clock source ADMUX |= (1<<REFS0); ADMUX &= ~(1<<REFS1); //Avcc(+5v) as voltage reference ADCSRB &= ~((1<<ADTS2)|(1<<ADTS1)|(1<<ADTS0)); //ADC in free-running mode ADCSRA |= (1<<ADATE); //Signal source, in this case is the free-running ADCSRA |= (1<<ADEN); //Power up the ADC ADCSRA |= (1<<ADSC); //Start converting for(;;){ //The infinite loop ADC_Read = ADCW; //Read the ADC value, really that's just it if(ADC_Read > 512){ PORTB |= (1<<PB5); //If ADC value is above 512 turn led on } else { PORTB &= ~(1<<PB5); //Else turn led off } } return 0; }
This example demonstrates the use of the ADC of a ATmega328 using the internal reference voltage To adapt to other AVR and / or other reference voltages see comments in this tutorial and in the data sheet
// This example demonstrates the use of the ADC of a ATmega169 // using the internal reference voltage of nominally 1.1 V // To adapt to other AVR and / or other reference voltages // see comments in this tutorial and in the data sheet /* Initialize the ADC */ void ADC_Init ( void ) { uint16_t result; // Select voltage reference for the ADC=> Avcc(+5v) ADMUX = (1<< REFS0); ADMUX &= ~(1<<REFS1); // Bit ADFR ("freerunning") in ADCSRA stands at power // already set to 0, ie single conversion ADCSRA = (1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0) ; // frequency prescaler ADCSRA |= (1<<ADEN) ; // enable ADC /* After activating the ADC is a "dummy readout" recommended reading So a value and rejects this in order to "warm up" the ADC */ ADCSRA |= ( 1 << ADSC ) ; // an ADC conversion while ( ADCSRA & ( 1 << ADSC ) ) { // wait for the conversion is complete } /* ADCW must be read once, otherwise the result of the next Conversion is not taken. */ result = ADCW; } /* ADC single measurement */ uint16_t ADC_Read (uint8_t channel) { // channel choose to influence without other bits ADMUX = (ADMUX &~ (0xF0))|(channel &0x0F) ; ADCSRA |= (1<<ADSC) ; // a "single conversion" while (ADCSRA & (1<<ADSC) ) { // wait for the conversion is complete } return ADCW; // ADC read and return } /* ADC with multiple measurement */ /* Note: Range of sum variables */ uint16_t ADC_Read_Avg (uint8_t channel, uint8_t nsamples) { uint32_t sum = 0 ; for (uint8_t i = 0; i< nsamples; i++ ) { sum += ADC_Read (channel) ; } return ( uint16_t ) ( sum/nsamples ) ; } /* Example calls: */ int main ( ) { uint16_t adcval; uint16_t adcval1; ADC_Init ( ) ; while ( 1 ) { adcval= ADC_Read(0) ; // channel 0 // do something with adcval adcval1= ADC_Read_Avg(2,4) ; // Channel 2, mean of 4 measurements // do something with adcval } } Reference (Part. 1) : http://dubworks.blogspot.co.uk/2012/08/beyond-gpio-pins-peripherals-intro-to.html