STM32F7 Disco ADC issue

[Grozea.Ion]

Posted on June 13, 2017 at 08:09

Hello all,

I am trying to read the ADC value from PA0 pin on a STM32F7 Disco board but without any success.

The issue is that the ADC reading is acting as the pin is floating

I suspect that the initialization code is not correct due to the fact that if i change the the Pull parameter to PULLUP/DOWN the behavior of the ADC value stays the same.

I have try to run also the example ADC_RegularConversion_DMA from STM32Cube_FW_F7_V1.7.0 but the behavior of the value is the same (i run the code on 2 different new boards)

I have attached the ADC code for review.

Can someone help me figure it out what is wrong here?

Thanks

#adc-reads #stm32f7-discovery

[AvaTar]

Posted on June 13, 2017 at 08:18

  sConfig.SamplingTime = ADC_SAMPLETIME_3CYCLES;

Perhaps the ADC input is actually 'floating'.

What are your timing requirements and attached analog input hardware (impedance) ?

[Grozea.Ion]

Posted on June 13, 2017 at 10:22

Hi,

Thank you for your replys. 

With ADC I intend to read a battery voltage from time to time

I have also tested 480cycles and the result is the same, also i am using a 10k to test the ADC, the pot is connected to 3.3V

[Jan Waclawek]

Posted on June 13, 2017 at 09:24

IMO 5V-tolerant pins disconnect pullup/pulldown when switched to analog mode.

JW

[AvaTar]

Posted on June 13, 2017 at 09:44

Perhaps I was a little cryptic.

I meant, 3 cycles is a

very

short sample time. If there is no adequate analog input driver, the value seems to float ...

[waclawek.jan]

Posted on June 13, 2017 at 10:08

[AvaTar]

Posted on June 13, 2017 at 10:20

Thinking I agree with you.

It has nothing to do with pull-up/pull-down configuration. It rather sounds like a deeper understanding of a SA-ADC is missing.

[waclawek.jan]

Posted on June 13, 2017 at 13:23

int main(void)

{    HAL_Init();    SystemClock_Config();    MX_GPIO_Init();    MX_ADC3_Init();    HAL_ADC_Start(&hadc3);    while (1)    {        //HAL_ADC_Start(&hadc3);        HAL_ADC_PollForConversion(&hadc, 100);        ADCValue = HAL_ADC_GetValue(&hadc);        //HAL_ADC_Stop(&hadc3);    }}

Where is hadc defined?

JW

[AvaTar]

Posted on June 13, 2017 at 12:05

I don't use Cube, so I won't comment on the full code.

I used to take provided examples for a specific peripheral (ADC in this case) and compared it with my code in such cases.

Assuming a proper signal on the ADC input pin, the issue was usually with the configuration.

Not sure what Cube is supposed to do here automatically, and how reliable ...

[Grozea.Ion]

Posted on June 13, 2017 at 15:28

Hi,

It is in main, extern ADC_HandleTypeDef hadc3;

Edit: Sorry, i have copied/paste the code, but the hadc 3 is correctly defined in adc.c and main.c

in the archive the 

extern ADC_HandleTypeDef hadc3; is missing.