Trying to read VREFINT using STM32F103C8t6 (Blue pill) and getting wrong value.

Forum|Forum|4 years ago
April 14, 2022
7 replies
5221 views

Hey,

I'm trying to read VREFINT value using internal ADC channel for vrefint, I'm converting data from ADC to voltage and getting 1.34-1.38 V. Datasheet says it should be 1.2-1.24 V. Why my reading has such error ? I'm using 238.5 sampling time for 8 MHz ADC clock, here is data reading code :

void ADC_VAL () {

HAL_ADC_PollForConversion(&hadc1,1);

ADC_VAL=HAL_ADC_GetValue(&hadc1);

voltage = (ADC_VAL*3.3/4095);

}

This topic has been closed for replies.

Michal Dudka

Lead

a) Your calculations are based on the 3.3V supply voltage. Are you sure that supply voltage is exactly 3.3V ?

b) Blue pill is often equiped with fake/clone STM chip and its internal reference does not have to be in specified limit.

c) ... some mistake in code (sampling time is not what you think etc.)

DSimp.1Author

Associate III

I'm using ST_LINK to power mcu and it is 3.3V . It might be fake chip but I quite trust shop where i bought this board. And what about mistakes in code? Why sampling time is wrong?

Michal Dudka

Lead

I dont mean to say that your sampling time is wrong, but just mention that it can be also your software bug. Just take voltmeter and measure "blue pill" VDD (VREF+) to rule out a). To rule out b) take some another board with same chip, like discovery or nucleo board where you can be sure that chip is genuine. Run your program and look for results.

Peter BENSCH

ST Technical Moderator

Then you divide by 4095, presumably because you set the ADC to 12bit, right? But why 4095 if it is 12bit, i.e. 2^12=4096?

Furthermore, did you perform a calibration as recommended by RM0008 in section 11.4?

It is recommended to perform a calibration after each power-up.

Regards

/Peter

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