ADC reading change rapidly

[Linda]

Posted on July 25, 2014 at 00:44

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[Tesla DeLorean]

Posted on July 25, 2014 at 02:02

Sample it slower, and less frequently. Reduce the ADC clock, increase the sample time.

[Linda]

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

[Tesla DeLorean]

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);

[raptorhal2]

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

[Linda]

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

[Tesla DeLorean]

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

?