采样值还是和内部参考电压值时差不多？

只看该作者 · 2018-12-2 16:30

用的是官方的EK-LM4F232H5QD评估板
其中PD4（AIN7）外接电池进行AD采样测试，电池电压1.528-1.533V左右，当设置参考电压为内部参考电压时，采样值在1827-1924，1.528/3.3*4096=1896左右，设置为外部3V参考电压时，采样值还是和内部参考电压值时差不多？

只看该作者 · 2018-12-2 16:30

12bit的adc，在参考电压与测试电压值都在较稳定的情况下，为什么AD采样值变化如此大？采用硬件多次平均，效果也不是特别好，ad值偏差也有几十个。
unsigned long ref=0xff;
int main(void)
{
   tContext sContext;
   char cText[8];
   unsigned long ulText;
   unsigned long ulADC0_Value[3];
   FPUEnable();
FPULazyStackingEnable();
SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ |       SYSCTL_OSC_MAIN);
   CFAL96x64x16Init();
   GrContextInit(&sContext, &g_sCFAL96x64x16);
   GrContextForegroundSet(&sContext, ClrWhite);
   GrContextFontSet(&sContext, &g_sFontFixed6x8);
GrStringDraw(&sContext,"ADC Hands On Lab", -1,1, 5, 0);
GrStringDraw(&sContext,"----------------", -1,1, 15, 0);
GrStringDraw(&sContext,"Ad:", -1,20, 25, 0);
SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
   GPIOPinTypeADC(GPIO_PORTE_BASE, GPIO_PIN_4 | GPIO_PIN_5 | GPIO_PIN_6);
ref=ADCReferenceGet(ADC0_BASE);
ADCReferenceSet(ADC0_BASE,ADC_REF_EXT_3V);
ref=ADCReferenceGet(ADC0_BASE);
   ADCSequenceConfigure(ADC0_BASE, SEQUENCER, ADC_TRIGGER_PROCESSOR, 0);
ADCSequenceStepConfigure(ADC0_BASE, SEQUENCER, 0, ADC_CTL_CH7 | ADC_CTL_IE
                     |ADC_CTL_END);
   ADCSequenceEnable(ADC0_BASE, SEQUENCER);
   ADCIntClear(ADC0_BASE, SEQUENCER);
   while(1)
   {
      ADCProcessorTrigger(ADC0_BASE, SEQUENCER);
      while(!ADCIntStatus(ADC0_BASE, SEQUENCER, false))
      {
      }
      ADCSequenceDataGet(ADC0_BASE, SEQUENCER, ulADC0_Value);
      usprintf(cText, " %d ", ulADC0_Value[0]);
      GrStringDraw(&sContext, cText, -1, 45, 25, 1);
      SysCtlDelay(SysCtlClockGet() / 12);
   GrFlush(&sContext);
   }
}