Making a simple +5 V voltmeter with ATMega32 ADC module

In the previous post, we have introduce about the ADC module of ATMega32. Actually the maximum reference voltage of the ADC is +5 V in usual. From this concept we can measure an input analog voltage input to any ADC channel at +5 V full scale reading.

The reading ADC value in the single ended conversion could be obtained from:

Reference voltage VREF is normally +5 V. Input voltage must not exceed +5 V.

To calculate the voltage, we can obtain it from:

 

In this example, I use ADC0 to read an analog input voltage fed from a POT. The POT varies an analog output voltage from 0 V to +5 V DC. The MCU displays the reading result of the voltage from 0.0 V to 5.0 V.

ADC0 read the input analog voltage. PortC and PortD drive a two-digit
SSD. The voltage reading is from 0.0 V to 5.0 V.

Source code is here:

#include <avr/io.h>
#define  F_CPU 4000000UL
#include <util/delay.h>
int main(void)
{ float voltage;
 char _voltage;
 char ssd[16]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,
  0x07,0x7F,0x6F,0x77,0x7C,0x39,0x5E,0x79,0x71};
    //PortC as output
    DDRC=0xFF;
    //PortD as output
    DDRD=0xFF;
    //PA0 or ADC0 as an analog input
    DDRA=0;
    //Turn on the ADC module
    ADCSRA|=(1<<ADEN);
    while (1)
    {
     //Start the conversion
     ADCSRA|=(1<<ADSC);
     //Wait for the completion
     while((ADCSRA&(1<<ADSC))==1);
     /*Convert ADC to voltage*/
     voltage=(ADCL+(ADCH<<8))*5.0/1024;
  voltage*=10;
  /*convert float to SSD data*/
  _voltage=(char)voltage;
  /*Displaying the Data*/
  PORTD=0x00;
  PORTC=ssd[_voltage/10]|0x80;
  PORTD=0x01;
  _delay_ms(10);
  PORTD=0x00;
  PORTC=ssd[_voltage%10];
  PORTD=0x02;
  _delay_ms(10);
    }
}

The ADC reading is 2.5 V analog voltage.

Back to main tutorial page ATMega32 tutorials in C with Atmel Studio 7.