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) ?

[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 ...

[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

[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 15:37

Hello AvaTar,

I have started to use cube when i switched to F7,  before i have only worked with F103 and i also did not used mxcube.

Until i will find examples that are not cube based i will have to stick to it due to the F7 complexity.

Now, if you have example that are not cube based can you share them? On the F7 i will use I2C, UART in DMA RxTx, EXTI and ADC, i have figure it myself how to deal with GPIO

:)

.

Once again, if you have non cube based examples please share them if you can.

Thanks

[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

[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.

[Grozea.Ion]

Posted on June 13, 2017 at 18:10

Hello all and thank you for your support. I have found the issue of my ADC problem, is not software, it is the poor soldering of the CN5 connector on both boards, basically only PF6/PF7 can be used on my boards, for the other to work i need to apply pressure on the connector from side. I will return the boards a ask for new ones because all Arduino connectors are faulty.

Best regards,