Re: [avr-chat] ADCW only returns 1023

[Ormund Williams]

On Wed, 2008-01-30 at 22:10 -0700, Mikey Sklar wrote:
> I recently built a circuit board to measure the temperature of the
> grease flowing through my car. The car is a old Mercedes running on
> Waste Vegetable Oil from restaurant dumpsters. I was able to upload my
> code and single step with gdb then I found a issue. The ADCW register
> reports back 1023 despite my sensors running a wide range of values
> between 1.9V - 5V.
> 
> Has anyone else seen this behavior before? 
> 
> Setup:
> - atmega169 (TQFP)
> - avarice (v2.5)
> - avr-gcc (4.0.2)
> - avr-libc (1.4.5)
> - avr-gdb (6.5)
> - jtag clone serial based programmer (MK-I only)
> - Mac OS/X 10.4.11
> 
> Code:
> 
> #include <avr/io.h>
> #include <avr/interrupt.h>
> 
> 
> #define SENSORS 2     // three thermistors measuring temperature (0-2)
> 
> 
> SIGNAL(SIG_ADC);
> int main (void);
> 
> 
> unsigned int adc_data;                //variable for ADC results
> unsigned int illuminate;      //led display pattern
> 
> 
> SIGNAL(SIG_ADC)               //ADC ISR
> {
>       
>       adc_data = ADCW;        //read all 10 bits into variable
> 
> 
>       /* ADC data from thermistors translated into five different hex values.
>          Hex values are stored for display to appropriate output LED port.
>          Shows driver grease temperature by illuminating LEDs.
>          The more LEDs that are on, the hotter the fuel is. */
> 
>       if ( adc_data <= 432 )
>               illuminate = 0x00;      // less than 65F - all lights off
>       else if ( adc_data > 432 && adc_data <= 530)
>               illuminate = 0x01;      // 65F - 85F   bin: 0001  dec: 1  hex: 
> 0x01
>       else if (adc_data > 530 && adc_data <= 770 )
>               illuminate = 0x03;      // 85F - 105F  bin: 0011  dec: 3  hex: 
> 0x03
>       else if (adc_data > 770 && adc_data <= 827)
>               illuminate = 0x07;      // 105F - 125F bin: 0111  dec: 7  hex: 
> 0x07
>       else if (adc_data > 827 && adc_data <= 1023)
>               illuminate = 0x0F;      // 135F+       bin: 1111  dec: 0  hex: 
> 0x0F
>       else 
>               illuminate = 0x00;      //error all lights off
> 
> 
>       if ( ADMUX == 0 ) {
>               PORTA = illuminate;     //store sensor results for display
>       }
>       else if ( ADMUX == 1 )  {
>               PORTC = illuminate;     //store sensor results for display
>       }
>       else if ( ADMUX == 2 ) {
>               PORTD = illuminate;     //store sensor results for display
>       }
>       else {
>               PORTA = 0x0A;           //MUX Error: 0101 (led pattern)
>               PORTC = 0x0A;           //MUX Error: 0101 (led pattern)
>               PORTD = 0x0A;           //MUX Error: 0101 (led pattern)
>       }
> 
> 
>       // rotate through sensors
>         if ( ADMUX < SENSORS  ) 
>               ADMUX += 1;             //change mux to next sensor
>       else 
>               ADMUX = 0;              //reset mux to first sensor
>               
> 
>       ADCSRA = ADCSRA | 0x40; //start the next conversion
> 
> }
> 
> 
> int main(void)
> {
>       DDRA=0x0F;              //LED output (first four pins)
>       DDRC=0x0F;              //LED output (first four pins)
>       DDRD=0x0F;              //LED output (first four pins)
>       ADCSRA=0xCE;            //ADC on, /64, interrupt enable, and started
>       ADMUX=0x00;             //ADC registers PF0, PF1, PF2 one at a time
You've cleared the bits REFS0 and REFS1 so you must connect a refrence
voltage to AREF (pin 62).
> 
>       PORTA = 0x0F;           //power on: 1111 (led pattern)
>       PORTC = 0x0F;           //power on: 1111 (led pattern)
>       PORTD = 0x0F;           //power on: 1111 (led pattern)
> 
>       sei();                  //global interrupt enable bit
> 
>       while(1) {
>       }
> }

__
Ormund