Reading ADC

[pranathi1091]

Posted on November 27, 2012 at 07:39

Hello All,

I am using STM32F2 series of controller. I want to monitor the battery voltage of my device which is connected to GPIO Pin 3 of port A which has alternate function of ADC1. Here is my code void RCC_Configuration(void) { RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);   //Enable ADC1 Clock   RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_DMA2, ENABLE); } void GPIO_Configuration(void) { GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;   GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;   GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;   GPIO_Init(GPIOA, &GPIO_InitStructure); }

volatile uint16_t ADC1ConveretedValue[64]=0;

volatile uint32_t ADC1ConvertedVoltage=0;  

 void DMA_Configuration(void)

  {      DMA_InitTypeDef DMA_InitStructure;

  /* DMA2_Stream0 channel0 configuration **************************************/

  DMA_DeInit(DMA2_Stream0);   DMA_InitStructure.DMA_Channel = DMA_Channel_0;    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)ADC1_DR_Address;   DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&ADC1ConveretedValue;   DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;   DMA_InitStructure.DMA_BufferSize = 64;   DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;   DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Disable;   DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;   DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;   DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;   DMA_InitStructure.DMA_Priority = DMA_Priority_High;   DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;           DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;   DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;   DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;   DMA_Init(DMA2_Stream0, &DMA_InitStructure);   /* DMA2_Stream0 enable */   DMA_Cmd(DMA2_Stream0, ENABLE);

   ADC_DMACmd(ADC1, ENABLE);

  }

void AdcInit(void)

  {   ADC_InitTypeDef       ADC_InitStructure;   ADC_CommonInitTypeDef ADC_CommonInitStructure;     /* ADC Common Init **********************************************************/   ADC_CommonInitStructure.ADC_Mode = ADC_Mode_Independent;   ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;   ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_Disabled;   ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_5Cycles;   ADC_CommonInit(&ADC_CommonInitStructure);

   /* ADC1 Init ****************************************************************/

  ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;   ADC_InitStructure.ADC_ScanConvMode = DISABLE;   ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;   ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;   ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;    ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;   ADC_InitStructure.ADC_NbrOfConversion = 1;   ADC_Init(ADC1, &ADC_InitStructure);

  ADC_RegularChannelConfig(ADC1,ADC_Channel_1,1,ADC_SampleTime_3Cycles);

  ADC_DMARequestAfterLastTransferCmd(ADC1, ENABLE);

  ADC_DMACmd(ADC1, ENABLE);

}

int8_t ReadADC1(void)

{  uint8_t TimeOut=2000;   ADC_RegularChannelConfig(ADC1, ADC_Channel_3, 1, ADC_SampleTime_3Cycles);    ADC_SoftwareStartConv(ADC1); // Wait until conversion completion    if(TimeOut>0)    {     while(ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC) == RESET); //Check End of Concersion Flag  return ADC_GetConversionValue(ADC1);  // Get the conversion value  TimeOut--;  }  else  return ADC_TIMEOUT_ERROR; }

int main(void)

{   ADC_InitTypeDef   ADC_InitStructure;  DMA_InitTypeDef DMA_InitStructure;    TIM_TimeBaseInitTypeDef   TIM_TimeBaseStructure;   TIM_OCInitTypeDef         TIM_OCInitStructure;    ADC_CommonInitTypeDef ADC_CommonInitStructure;   /* System clocks configuration ---------------------------------------------*/   RCC_Configuration();     /* GPIO configuration ------------------------------------------------------*/   GPIO_Configuration();     DisplayInit();

  DMA_Configuration();

  AdcInit();

      while(1)   {  uint8_t ConvertedValue;   ConvertedValue=ReadBatteryVoltage();  DisplaySetPos(0,0);  DisplayWriteData(ConvertedValue);  Delay_M(200);  DisplayWriteCmd(DISPLAY_CMD_CLR);  delay(20);   }       /* does not exit - kind of important */       return 0; }

int8_t ReadVoltage()

{ uint8_t ConvertedValue;   ConvertedValue=ReadADC1();   return  ConvertedValue; } I cannot see any output from ADC.Could anyone pls let me know if anything is missed out or something wrong #vbat-monitoring #adc #stm32

[Tesla DeLorean]

Posted on November 27, 2012 at 16:07

3 Cycles is probably too quick to get a stable measurement.

Decide if you're using DMA or polling, DMA will copy values into the buffer defined for it, read the values in the buffer and convert the 12-bit value by scaling against VDDA (VREF). The ADC will not be able to measure voltages that exceed VDDA The ADC has a VBAT channel for the battery supply pin of the device. Don't use 8-bit variables to pass 12/16-bit content.

[pranathi1091]

Posted on November 28, 2012 at 05:45

Thanks Clive

I have changed sampling time to ADC_SampleTime_15Cycles. I have decided to use DMA.DMA will copy values into the buffer defined for it, read the values in the buffer    The buffer i have defined is ADC1ConveretedValue DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&ADC1ConveretedValue;So i have to read this. Please let me know if i am correct. Could u pls tell me more about converting 12 bit value by scaling against VDDA. Thanks

[Tesla DeLorean]

Posted on November 28, 2012 at 06:28

Well it's reading constantly into an array, you'd probably want

DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&ADC1ConveretedValue[0]; // For a 3.3V reference/supply something like float voltage; voltage = ((float)(ADC1ConvertedValue[0] & 0xFFF) * 3.3) / 4096.0; int millivolts; millivolts = ((int)(ADC1ConvertedValue[0] & 0xFFF) * 3300) >> 12;

[Nickname12657_O]

Posted on November 28, 2012 at 11:20

Hi,

In the STM32F2 StdPeriph_Lib package, there is a similar example (VBAT_Measurement). It takes into account that the VBAT pin is internally connected to a bridge divider by 2 to avoid exceeding VDDA (VBAT/2 connected to ADC1_IN18). Cheers, STOne-32