Question
STM32F103RET6 ADC reads voltage with no voltage at pin
Posted on April 06, 2014 at 20:01
If i read any of the ADC's i see a voltage of about 1736mv it changes a little depending on the sampling speed, i've used non continuous reads, and continuous DMA , both mostly the same, reads the same in circuit or out. if i put 2v6 on it, it'll read it exactly correct, same at 0v
i've used stm32lib, in different ways but always the same. i have all the vss gnd, vdd 3v3, vdda via a ferrite to 3v3 with a 10uF and 100nF cap to vssa. 72mhz speed with external 8mhz xtal. am i just completely misunderstanding something? input voltages are stable schematic http://i.imgur.com/AfaWwpng its a larger project, i cut out the adc part, i can make a simpler full example if nothing obvious or misunderstand on my part.ADC_RegularChannelConfig ( ADC1, ADC_Channel_0, 1, ADC_SampleTime_55Cycles5 );
ADC_SoftwareStartConvCmd ( ADC1 ,ENABLE ); //Start the conversion
while ( ADC_GetFlagStatus ( ADC1, ADC_FLAG_EOC ) == RESET ); //Processing the conversion
return ADC_GetConversionValue ( ADC1 ) /4; //Return the converted datavoid ADC_Configuration ( void )
{
ADC_InitTypeDef ADC_InitStructure;
#if DMA_ADC == 1
DMA_InitTypeDef DMA_InitStructure;
memset ( &DMA_InitStructure,0,sizeof ( DMA_InitStructure ) );
memset ( &ADC_InitStructure,0,sizeof ( ADC_InitStructure ) );
/* Enable DMA1 clock */
RCC_AHBPeriphClockCmd ( RCC_AHBPeriph_DMA1, ENABLE );
/* Enable ADC1 clock */
RCC_APB2PeriphClockCmd ( RCC_APB2Periph_ADC1, ENABLE );
/* DMA1 channel1 configuration ---------------------------------------------*/
DMA_DeInit ( DMA1_Channel1 );
DMA_InitStructure.DMA_PeripheralBaseAddr = ADC1_DR_Address;
DMA_InitStructure.DMA_MemoryBaseAddr = ( u32 ) &ADC_Ampl[0];
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
DMA_InitStructure.DMA_BufferSize = 2;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
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_Low;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init ( DMA1_Channel1, &DMA_InitStructure );
/* Enable DMA1 channel1 */
DMA_Cmd ( DMA1_Channel1, ENABLE );
/* Disable the DMA1 Channel1 Transfer complete interrupt */
DMA_ITConfig ( DMA1_Channel1, DMA_IT_TC, DISABLE );
#else
/* Enable ADC1 clock */
RCC_APB2PeriphClockCmd ( RCC_APB2Periph_ADC1, ENABLE );
#endif
/* ADC1 configuration ------------------------------------------------------*/
ADC_InitStructure.ADC_Mode = ADC_Mode_Independent;
#if DMA_ADC == 1
ADC_InitStructure.ADC_ScanConvMode = ENABLE;
ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;
#else
ADC_InitStructure.ADC_ScanConvMode = DISABLE;
ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;
#endif
ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None;
ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
ADC_InitStructure.ADC_NbrOfChannel = 2;
ADC_Init ( ADC1, &ADC_InitStructure );
/* ADC0 regular channel configuration */
ADC_RegularChannelConfig ( ADC1, ADC_Channel_0, 1, ADC_SampleTime_239Cycles5 );
/* ADC1 regular channel configuration */
ADC_RegularChannelConfig ( ADC1, ADC_Channel_1, 2, ADC_SampleTime_239Cycles5 );
#if DMA_ADC == 1
/* Enable ADC1 DMA */
ADC_DMACmd ( ADC1, ENABLE );
#endif
/* Enable ADC1 */
ADC_Cmd ( ADC1, ENABLE );
/* Enable ADC1 reset calibaration register */
ADC_ResetCalibration ( ADC1 );
/* Check the end of ADC1 reset calibration register */
while ( ADC_GetResetCalibrationStatus ( ADC1 ) );
/* Start ADC1 calibaration */
ADC_StartCalibration ( ADC1 );
/* Check the end of ADC1 calibration */
while ( ADC_GetCalibrationStatus ( ADC1 ) );
}memset ( &GPIO_InitStructure,0,sizeof ( GPIO_InitStructure ) );
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1 ;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init ( GPIOA, &GPIO_InitStructure );