[SOLVED] wrong voltage on adc in atmega 8!

[samna_asadi]

hi
i have written a program to read lm35 temp sensor from adc4 on atmega8.
i`ve already set the DDRC to 0x00 but its giving me wrong number.i tried to manually measure the voltage on lm35 and atmega`s pin , on lm35 side it was 0.34 that was good but on the atmega it was 1.2 or 3 and when i connect lm35 to adc4 pin the voltage change to something else that is not right!
i`ve connected lm35 straight to atmega.
what can i do with it , what`s the problem?
tnx

 

[bigdogguru]

Post your entire code listing so that we can review and offer advice.

BigDog

 

[john120]

Post your entire code listing so that we can review and offer advice.

BigDog

Try to submit all of your codes for advice.

 

[samna_asadi]

ok tnx for reply...

#define  F_CPU 8000000UL
#include <avr/io.h>
#include <avr/interrupt.h>
#include "d:\D\e\electronic\library\lcdlibv20\lcd.c"


void screen();

int main(void)
{
	_delay_ms(1000);
	
	
	
	
	
	DDRC=239;
	DDRB=254;
	DDRD=31;
	PORTD=248;
	PORTB=255;
	ADMUX=0b00000100;
	ADCSRA=0b10100110;
	

	LCDInit(0);
	LCDCmd(12);

	ADCSRA |= 64;
	
   while(1)
   {
	screen();
	 _delay_ms(1000);  
   }
   
}


void screen()
{
		
	LCDWriteStringXY(10,1,"      ");
	LCDWriteIntXY(10,1,(ADCL+(ADCH>>8)/2),-1);
	
	
}

it just show 4 or 5 on the screen.
tnx.

 

[jayanth.devarayanadurga]

---

Code C - [expand]
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unsigned char lowbyte;
unsigned int adcres;
 
 
lowbyte = ADCL;
adcres = ADCH;
adcres = adcres<<8 | lowbyte;
LCDWriteIntXY(10,1,adcres);

---

 

[samna_asadi]

---

Code C - [expand]
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unsigned char lowbyte;
unsigned int adcres;
 
 
lowbyte = ADCL;
adcres = ADCH;
adcres = adcres<<8 | lowbyte;
LCDWriteIntXY(10,1,adcres);

---

can u explain more?

 

[jayanth.devarayanadurga]

lowbyte is 8-bit waid, adcres is 16-bit wide. ADCL is stored in lowbyte. ADCH is stored in adcres and shifted 8 bits so that ADCH will be in the high byte of adcres. adcres is ored with lowbyte. result is adcres.

eg: lowbyte = 0xAB, ADCH = 0xDE.

adcres = 0xDE
adcres = 0xDE00
adcres = 0xDEAB

 

[samna_asadi]

tnx for for the replay.that right shift was my mistake but the problem still exist.its my first time for using adc, and i don`t know how its gonna be but the adc4 is on 1.295 volt and when lm35 with 0.34 volt connect to this pin its 1.293 volt and adc doesn`t get the right result!!
i don`t know whats wrong if u could help!

 

[jayanth.devarayanadurga]

Post schematic and full code so that it can be fixed.

 

[samna_asadi]

#define  F_CPU 8000000UL
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util\delay.h>
#include "d:\D\e\electronic\library\lcdlibv20\lcd.c"


void screen();

int main(void)
{
	_delay_ms(1000);
	
	
	
	
	
	DDRC=239;
	DDRB=254;
	DDRD=31;
	PORTD=248;
	PORTB=255;
	ADMUX=0b00000100;
	ADCSRA=0b10100110;
	

	LCDInit(0);
	LCDCmd(12);

	ADCSRA |= 64;
	
	while(1)
	{
		screen();
		_delay_ms(1000);
	}
	
}


void screen()
{
	
	LCDWriteStringXY(10,1,"      ");
	LCDWriteIntXY(10,1,((ADCL | (ADCH<<8))/2),-1);
	
	
}

 

[alexan_e]

You should comment your code so that we know what you are trying to do
code like

DDRC=239;
	DDRB=254;
	DDRD=31;
	PORTD=248;
	PORTB=255;
	ADMUX=0b00000100;
	ADCSRA=0b10100110;

doesn't make any sense unless you use a calculator to convert decimal to binary for the ports and check the datasheet for the function of each bit of the ADC registers.

You are using an LCD library, are you sure it is not messing up the pin direction of the PC4 pin?

 

[jayanth.devarayanadurga]

Where is ADC read routine?

 

[samna_asadi]

You are using an LCD library, are you sure it is not messing up the pin direction of the PC4 pin?

i was going to say that "i`ve already check the header file" but i figured maybe there is something wrong with the micro and there was, i changed the micro and problem solved, maybe it was some power leakage...
tnx any way for giving me your time.