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Problem with ADC in atmega8 (multimeter)

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Kaminari

New Member
Hello.

I've got problem while measuring voltage.
First of all, ADC3 is working perfectly BUT ADC4 and 5 not.

I don't think it's a problem from circuit because I measured voltage on the pin and it was about 1.55V
Voltage ref = 2.73V so it should be about (result/1023) = 0.567. Yet it shows something like 0.005

When I disconnect anything it shows full 1. I think it's a problem with my code or it's optimization by compiler.
I don't think I could destroy ADC inside Atmega because it's basicly one with MUXED input.

THIS code works:
Code:
ADMUX = 192 | 3; //ADC3 with internal reference
		ADCSRA = ADCSRA | (1<<ADSC);	// Start ADC conversion
		while(!(ADCSRA & (1<<ADIF)))	// Wait for AD interrupt flag
			;		
		adResult = ((ADCL) | ((ADCH)<<8));	// Shift high and low to 10-bit	
		voltage = (0.0252113*adResult);
But not the others. Maybe MUX is not 3 2 1 0 but 0 1 2 3 ?
What is wrong here?

Here is my code:
Code:
#include <avr/io.h>
//#include <math.h>	// Needed for trunc function
#include <util/delay.h>
#include <stdlib.h> 
#include <D:\Archiwum\AVR\Projekty\Multi\HD44780.h>

/* Function Definitions */
void ioinit(void);

// SBI and CBI to set/clear bits
#define sbi(port_name, pin_number)   (port_name |= 1<<pin_number)
#define cbi(port_name, pin_number)   ((port_name) &= (uint8_t)~(1 << pin_number))

uint8_t DPStatus = 0x00;
volatile uint8_t resDP = 0;


int main()
{
	float adResult = 0;
	float voltage = 0;
	float current1 = 0;
	float current2 = 0;

	ioinit();

	LCD_Initalize();


	while(1)
	{	// Every loop starts with ADC measurement
		// measurement is processed and display updated
		ADMUX = 192 | 5; //ADC5 with internal reference
		ADCSRA = ADCSRA | (1<<ADSC);	// Start ADC conversion
		while(!(ADCSRA & (1<<ADIF)))	// Wait for AD interrupt flag
			;		
		adResult = ((ADCL) | ((ADCH)<<8));	// Shift high and low to 10-bit	
		current1 = (adResult/1023);

		
		ADMUX = 192 | 3; //ADC3 with internal reference
		ADCSRA = ADCSRA | (1<<ADSC);	// Start ADC conversion
		while(!(ADCSRA & (1<<ADIF)))	// Wait for AD interrupt flag
			;		
		adResult = ((ADCL) | ((ADCH)<<8));	// Shift high and low to 10-bit	
		voltage = (0.0252113*adResult);

		
		

		ADMUX = 192 | 4; //ADC4 with internal reference
		ADCSRA = ADCSRA | (1<<ADSC);	// Start ADC conversion
		while(!(ADCSRA & (1<<ADIF)))	// Wait for AD interrupt flag
			;		
		adResult = ((ADCL) | ((ADCH)<<8));	// Shift high and low to 10-bit	
		current2 = (adResult/1023);

		float mcurrent = (voltage - current2);

		LCD_GoTo(1,0);
		if (voltage <10) LCD_WriteText("0");
		char volt[5] = "     "; 
		dtostrf(voltage,3,3,volt);
		LCD_WriteText(volt);
		LCD_WriteText("V ");

		if (current1 <10) LCD_WriteText("0");
		char amp[5] = "     "; 
		dtostrf(current1,3,3,amp);
		LCD_WriteText(amp);
		LCD_WriteText("A ");

		char mamp[5] = "     ";   
		dtostrf(mcurrent,3,3,mamp);
  		LCD_GoTo(1,1);
		LCD_WriteText("Limit: ");
		LCD_WriteText(mamp);
		LCD_WriteText("A ");
		_delay_ms(50);


	}

	return 0;
}

void ioinit(void)
{

	DDRD = 0xFF;	// Set data direction for port D (A,B,...,G)
	PORTD = 0;	// Initialize all segments off

	DDRB = 0b00000111;	// Set data direction for digits and button (PB5)
	PORTB = 0;	// All digits off, button high

	DDRC = 0b00000000;	// PC0-2 are input, rest output

	/* Set up ADC */
	ADCSRA = (1<<ADEN);	// Enable ADC

}
 

BillBodw

New Member
microchip

microchip site wen i last looked had heaps of full working circuits and software for there line of products u could download there script for it then mod it for ur chip
 

wkrug

Active Member
I would put a little Capacitator at the Input Pins about 1..10nF should be enough.
After switching the A/D Input Multiplexer wait a little, bit before start A/D Conversation.
That should solve the Problem.

The 100nF Capacitator at the AREF Pin is included and AVCC has power?
 
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