ATMega32 50 Volts DC Digital Voltmeter

Analog To Digital Converter (ADC) Module

The ADC module relates only with analog voltage value from any analog-output sensors or other analog circuits. Analog voltage value could be scaled to a smaller range value by using a two-resistor voltage divider circuit. For example a 50 V DC voltage could be scale to a range of lower than 5 V DC because the maximum analog reference voltage of ADC module of this device is +5 V DC.

ADC Scaling Circuit Using Voltage Divider Rule

For the voltage divider of two resistor, I do a calculation as follow.

 

x2

x1.5

x1

x0.5

00:00 / 00:00

• Pause
• Unmute
• Fullscreen
• Fluid Player 3.51.0

V (ADC) is the analog voltage fed to the ADC pin. It's the measuring voltage divided by 11, or 0.09 of the measuring voltage.

Using these two values of resistor, we could measure the analog voltage up to 50 V DC.

Program For Digital Voltmeter

A sample of program. The voltage reading is 26.37 Volts.

Atmel Studio C source code. Click here to download source file.

 

	#include <avr/io.h>
	#define F_CPU 4000000UL
	#include <util/delay.h>
	int adcResult;
	void displayVoltage(){
	char ssd[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x07,0x7F,0x6F};
	float voltage;
	unsigned int voltageDisplay;
	/*make the input voltage with some error correction
	the actual value is 0.09*/
	voltage=0.11*(adcResult*5)/1024;
	/*convert the floating-point voltage to integer
	for displaying*/
	voltageDisplay=(voltage*10000);
	PORTD=0x00;
	PORTC=ssd[voltageDisplay/1000];
	PORTD=0x01;
	_delay_ms(10);
	PORTD=0x00;
	PORTC=ssd[(voltageDisplay%1000)/100]|0x80;
	PORTD=0x02;
	_delay_ms(10);
	PORTD=0x00;
	PORTC=ssd[(voltageDisplay%100)/10];
	PORTD=0x04;
	_delay_ms(10);
	PORTD=0x00;
	PORTC=ssd[voltageDisplay%10];
	PORTD=0x08;
	_delay_ms(10);
	PORTD=0x00;
	PORTC=0x3E;
	PORTD=0x10;
	_delay_ms(10);
	}
	int main(void)
	{
	//PortC as output
	DDRC=0xFF;
	//PortD as output
	DDRD=0xFF;
	//PORTA is analog input
	DDRA=0;
	//Select AD7
	ADMUX|=0x07;
	//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);
	_delay_ms(25);
	//Read the result
	adcResult=ADCL+(ADCH<<8);
	displayVoltage();
	}
	}

view raw m32Adc50vDvm.c hosted with ❤ by GitHub

Schematic diagram is here.

The CPU clocks at 4 MHz. The display made up to five distinct single-digit SSDs.

Back to main tutorials page.