Reading ADC with STM32H750 Discovery Kit

[RHerg.1]

i want to read out a single ADC (temperature sensor) via polling method and want to display the result on the Display. On the backside of the board are some standard arduino connectors, i used them to connect the temperature sensor (CN7 -> A0 -> PC0 ).

The problem is, that it is not working despite i used only standard code in the default task for reading it:

void StartDefaultTask(void *argument)
{
 /* USER CODE BEGIN 5 */
 uint16_t adcvalue;
 /* Infinite loop */
 for(;;)
 {
 
 
 HAL_ADC_Start(&hadc1);
 HAL_ADC_PollForConversion(&hadc1, 100);
 adcvalue = HAL_ADC_GetValue(&hadc1);
 HAL_ADC_Stop(&hadc1);
 
 
 
 int resolution = 4096;
 
 
 resistance1 = 10000*((adcvalue/(double)resolution)/(1-(adcvalue/(double)resolution)));
 
 
 Temp1 = 1/((1/298.15)+((double)1/3435)*log((double)resistance1/10000));
 
 
 
 Temp1 = Temp1 - 273.15;
 
 
 
 osDelay(20);
 }
 /* USER CODE END 5 */
}

[RHerg.1]

Hello, i don't want to read out the internal temperature Sensor. I want to read 3 external Sensors, but first i started with 1 sensor.