STM32F091RC-Nucleo ADC Sequencer example not producing correct results

[MBill.1]

Hi,

I'm using the STM32F091RC-Nucleo ADC sequencer example to understand the ADC initialization but I'm not getting accurate results. It looks like the example uses PA4 on the board:

/* main.h */

#define ADCx_CHANNELa_GPIO_PORT        GPIOA

#define ADCx_CHANNELa_PIN              GPIO_PIN_4

I have a power supply connected to a PA4 and when I adjust the voltage from the 0 -> 3.3 volts (which should be Vref for the ADC), I get meaningless results. These are the results for the ADC values read at PA4, when I apply 1.0 V:

/* main.c */

uhADCChannelToDAC_mVolt   = COMPUTATION_DIGITAL_12BITS_TO_VOLTAGE(aADCxConvertedValues[0]);

1441

1441

1437

1438

1444

And these are the values read when I apply 2.0 V:

1432

1428

1427

1427

1437

The ADC readings are effectively the same for 1.0 volts or 2.0 volts.

Can anybody advise on what's going wrong?

[TDK]

> I have a power supply connected to a PA4 

Is your power supply ground connected to the board ground as well?

You could also just connect PA4 to GND or 3V3 to test.

[MBill.1]

Yes, the power supply ground is connected to the board ground. I connected 3.3 volts from the board to PA4 and these are the results (I'm expecting something close to 4095 - full-scale):

1728

1797

1854

1793

1831

And these are the readings when ground is connected (I'm expecting something close to 0):

1824

1757

1809

1874

1769

[MBill.1]

Can anyone advise on how to debug this issue? I imagine that the hardware on the Nucleo boards is correct.

[TDK]

You haven't really posted enough information to debug. Clearly something is wrong, probably in code, but it's not any of the 3 lines of source you've provided.

[MBill.1]

I've posted that "I'm using the STM32F091RC-Nucleo ADC sequencer example" (it's the first line in the post), and I'm targeting the STM32F091RC-Nucleo development board. Should I post the relevant initialization from the example? Those lines are posted were from where I was extracting the ADC readings.