Reading temperature from adc value(Non linear)

[sireevenkat1]

Hi,

I am using STM32G491RE. I have to read temperature values from ADC. We  used voltage divider circuit to map the voltage values with temperature values it is non linear change between volatge and temperature.

I tried below way

const uint16_t adc_values[182] = {/* mention all voltage values*/};

const uint16_t temperature_values[182]={/* mention corresponding temperature values*/};

const int calibration_points = sizeof(adc_values) / sizeof(adc_values[0]);

float mapADCtoTemperature(uint16_t adc_value) {

for (int i = 0; i < calibration_points; i++) {

if(adc_value==adc_values[i])

{

return temperature_values[i];

}

}

return -1.0;

}

 

while(1)

{

HAL_ADC_Start(&hadc1);

HAL_ADC_PollForConversion(&hadc1, HAL_MAX_DELAY);

uint16_t adc_value = HAL_ADC_GetValue(&hadc1);

float voltage=(float)adc_value/4095.0 * 3.3;

float temperature = mapADCtoTemperature(voltage);

char buff[100];

sprintf(buff,"ADC value: %d,voltage:%.2f V,Temperature: % .2f C\r\n",adc_value,voltage,temperature);

}

 

With above code I am getting only few correct temperature values.Is there any other way to do it.
Can anyone suggest.

Thanks

 

[######]

Edited as I misread the question.

[sireevenkat1]

HI @###### ,

Thanks for the suggestion but I am not using internal temperature sensor for temperature values reading. I am using voltage divider circuit(it has two resistor and one variable resistor) for temperature and voltage values mapping.
What will be the TS_CAL2 & TS_CAL1 values if I am not using internal temperature sensor?
I already have manually calculated temperature values for given voltage values . I just want to know how to get that temperature values for given voltage values through programming with stm32G491RE.

Thanks

[######]

Sorry, didn't read your question properly, I'll edit. The only thing possibly useful in what I posted above might be the internal reference data that is also stored.

I would guess if you are getting a non-linear result then you are using a non-linear NTC thermistor? I think there are some packaged linear thermistors available that have a PTC.

Alternatively I would suggest you create and store a Look Up Table in ROM of calibrated values and then a function to interpolate and find an estimate nearest value.

There might be a mathematical method to fit a curve to the response but I wouldn't know how to do this.

[Billy OWEN]

Hi @sireevenkat1 

 

The forum moderator had marked your post as needing a little more investigation and direct support. An online support case has been created on your behalf, please stand by for just a moment and you will hear from us.

 

Regards,

Billy

[sireevenkat1]

Issue is solved. Thanks for suggestions. In my application voltage mapping with temperature already done by hardware team I just need to check the voltage values based on that need to perform the action.

Thanks