I am using a Mega88 running on its internal 8M clock to measure 2 voltages, using 10bit resolution, and output them on a LCD. Sounds simple enough.
ADC(1) and ADC(2) are used.
I get strange results. the output on the display seems to be unstable and varies over a wide range. if I comment out the first conversion, ADC(1), I get the correct result for ADC(2). Likewise if I then comment out the second conversion ADC(2), I get the correct result for ADC(2).
Here is my code to set up the ADC
ADMUX=(1<<REFS0); // For Aref=AVcc; ADCSRA=(1<<ADEN)| (1<<ADPS2)| (1<<ADPS0)| (1<<ADPS1); //prescalar div factor =128 DIDR0 = 0xff; // Disable the digital Function for PORTC
This is how I am reading the ADC
uint16_t ReadADC(uint8_t ch)
{
//Select ADC Channel ch must be 0-7
ch=ch&0b00000111;
ADMUX|=ch;
//Start Single conversion
ADCSRA|=(1<<ADSC);
//Wait for conversion to complete
while(!(ADCSRA & (1<<ADIF)));
//Clear ADIF by writing one to it
ADCSRA|=(1<<ADIF);
return(ADC);
}
and finally this the portion of my main code
int16_t temp; temp = ReadADC(1)*40; utoa( temp , dig, 10); lcd_gotoxy(2,0); lcd_puts(dig); temp = ReadADC(2)*5; utoa( temp , dig, 10); lcd_gotoxy(2,1); lcd_puts(dig);
I understand the output on the display will be unformatted.
I think maybe I am running out of stack but am not sure. Any pointer as where I should look to fix this would be greatly appreciated.
