ADC reading change rapidly

Posted on July 25, 2014 at 13:51

Dear Clive 1

I am using STM32Cube_FW_F4_V1.1.0\Projects\STM32F429I-Discovery\Examples\ADC\ADC_RegularConversion_DMA

How to change frequently and  sample time?

Thanks

Posted on July 25, 2014 at 14:41

  /* 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);

  /* ADC3 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(ADC3, &ADC_InitStructure);

  /* ADC3 regular channel13 configuration *************************************/

  ADC_RegularChannelConfig(ADC3, ADC_Channel_13, 1, ADC_SampleTime_3Cycles);

Posted on July 25, 2014 at 16:09

The example uses ADC3 channel 8 on PF10. On the 429 Disco this pin is dedicated to LCD Enable, with a 4.7K pull down resister. Did you modify the example to use one of the 3 freely available ADC channels ?

Cheers, Hal

Posted on July 26, 2014 at 12:11

Thanks for help.

I change ADC3 channel 8 to PC3. I feel something wrong here.

The voltage being monitored is around 1.4v, but once connect with PC3, the voltage drop to to 0.8v.

How to fix it?

Thanks

Posted on July 26, 2014 at 13:13

How to fix it?

Use an OpAmp, or otherwise figure out why your signal is incapable of providing sufficient current into the unbuffered input.

What is

http://www.planetanalog.com/author.asp?section_id=510&doc_id=559252

?