AVR-Chat

Hello Everyone,

I am trying to measure the temperature on STK502 on
Atmega169P. I have followed the diagrams and I believe
the connections are right, but I am getting the wrong
results!  The function I am using to do the
calculations is:

float Temp_calculation(int ADC_value)
{
    float V_ADC;
	float Temperature;
	char  oper;

    if((ADMUX & 0x1F) == SingleEnded)       // check
if Single_ended operation

        V_ADC = (ADC_value * V_ref)/1024;      //
calculate the voltage over the NTC

    else if((ADMUX & 0x1F) == Differential) // check
if Differential operation

        V_ADC = (ADC_value * V_ref)/512;       //
calculate the voltage over the NTC

	    Temperature = (Beta /
(((log(V_ADC/(V_ref-V_ADC))/log(__E)) +
(Beta/T_amb)))) - T_zero;   // calculate the
temperature

	return Temperature;
}

where     V_ref     1.263    voltage-reference
          Beta     (3450.000)    // the Beta-value for
the NTC transitor
          R_th     (10000.00)    // the thermistor
resistance @ 25 degree Celsius
          T_amb    (298.0000)    // the temperature in
Kelvin for 25 degree Celsius
          T_zero   (273.0000)    // the temperature in
Kelvin for 0 degree Celsius
	  log(__E) (2.303)

This is the formula given in the manual, so I am not
sure why this is not working! Please let me know what
formula you may have used in your code.

Thanks,

Irene






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