analog.c

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/*--------------------------------------------------------------------------*
* Analog input helpers
*---------------------------------------------------------------------------*
* 15-Apr-2014 ShaneG
*
* These functions provide simple and accurate analog value reading.
*--------------------------------------------------------------------------*/
#include <avr/io.h>
#include "iohelp.h"

void adcInit(ANALOG adc) {
  // Make sure the ADC convertor is setup
  ADCSRA = (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0);
  // Switch off digital for the appropriate pin
  uint8_t mask, didr;
  if(adc==ADC0) {
    mask = 1 << PINB5;
    didr = 1 << ADC0D;
    }
  else if(adc==ADC1) {
    mask = 1 << PINB2;
    didr = 1 << ADC1D;
    }
  else if(adc==ADC2) {
    mask = 1 << PINB4;
    didr = 1 << ADC2D;
    }
  else if(adc==ADC3) {
    mask = 1 << PINB5;
    didr = 1 << ADC3D;
    }
  else // ADC4 or invalid pin, just ignore it
    return;
  // Make sure the pin is an input and pull up is disabled
  PORTB &= ~mask;
  DDRB &= ~mask;
  // Disable digital input for the pin
  DIDR0 |= didr;
  }

uint16_t adcRead(ANALOG adc, uint8_t skip, uint8_t average) {
  // Change the reference voltage and select input
  uint8_t muxval = adc;
  if(adc==ADC4) // Need 1.1V reference
    muxval = 0x80 | adc;
  ADMUX = muxval;
  // Start the conversion
  uint8_t count = skip + average;
  uint16_t value, total = 0;
  while(count) {
    // Start the conversion, then wait for it to finish
    ADCSRA |= (1 << ADSC);
    while(ADCSRA & (1 << ADSC));
    if(count<=average) {
      // Read the current value and add it to the running total
      value = ADCL;
      value = value | (ADCH << 8);
      total += value;
      }
    count--;
    }
  return (total / average);
  }