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Pablito Parseval
Pablito Parseval
Associate II
May 8, 2019
Question

Noise problem with ADC

  • May 8, 2019
  • 4 replies
  • 1984 views

Good morning,

I have a problem with the adc converter of the microcontroller stm32L053. I am in the prototype state and am using the Discovery Board.

I only have the analog AN0 pin connected to ground. When I execute the reading the converter does not return 0 and I have ./- 5LSB of noise. Is there something I'm wrong about?

0690X000008BQzUQAW.png

Below the ADC Configuration:

/* ADC init function */

static void MX_ADC_Init(void)

{

 ADC_ChannelConfTypeDef sConfig;

  /**Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion) 

  */

 hadc.Instance = ADC1;

 hadc.Init.OversamplingMode = DISABLE;

 hadc.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV16;

 hadc.Init.Resolution = ADC_RESOLUTION_12B;

 hadc.Init.SamplingTime = ADC_SAMPLETIME_39CYCLES_5;

 hadc.Init.ScanConvMode = ADC_SCAN_DIRECTION_FORWARD;

 hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc.Init.ContinuousConvMode = DISABLE;

 hadc.Init.DiscontinuousConvMode = DISABLE;

 hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;

 hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;

 hadc.Init.DMAContinuousRequests = DISABLE;

 hadc.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

 hadc.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 hadc.Init.LowPowerAutoWait = DISABLE;

 hadc.Init.LowPowerFrequencyMode = DISABLE;

 hadc.Init.LowPowerAutoPowerOff = DISABLE;

 if (HAL_ADC_Init(&hadc) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

  /**Configure for the selected ADC regular channel to be converted. 

  */

 sConfig.Channel = ADC_CHANNEL_0;

 sConfig.Rank = ADC_RANK_CHANNEL_NUMBER;

 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

  /**Configure for the selected ADC regular channel to be converted. 

  */

 sConfig.Channel = ADC_CHANNEL_VREFINT;

 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

}

This topic has been closed for replies.

4 replies

Uwe Bonnes
Uwe Bonnes
Chief
May 8, 2019

Do not look at the translated values. Look at the digits. If the steps in tour diagramm translate to digit and are not by some calculation clipping that is +/- 4 LSB max. That does not sound to bad.

RomainR.
RomainR.
ST Employee
May 9, 2019

You should do an ADC Calibration (on time) before start a conversion​. This will remove ADC Offset Error.

Take a look in your STM32Cube Repository ADC example.

/* ### - 2 - Start calibration ############################################ */
 if (HAL_ADCEx_Calibration_Start(&hadc, ADC_SINGLE_ENDED) != HAL_OK)
 {
 Error_Handler();
 }

Also, if you use STM32L0538DISCOVERY kit, note thay WakeUp Blue user button is shared with PA0 pin.

Best regards

rrom

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Pablito Parseval
Pablito ParsevalAuthor
Associate II
May 9, 2019

I try the calibration and the offset return to 0. The noise is alwais +/-5 digit.

I try to implement a mean to 8 sample, but i don't like this solution.

RomainR.
RomainR.
ST Employee
May 11, 2019

Hello Pablito,

I've tried to reproduce by using NucleoL053, and PA0 wired to GND.

My code use the same ADC setup (but without VREF_INT Channel) and perform ADC conversion on PA0 and fill a buffer of 64 samples.

Below my resuts are 0 with +2 lsb max .

Could you share your code please ?

BR

rrom

0690X000008BYlHQAW.png

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