怎么测量AVDD引脚或VDD引脚

是的，但是你可能需要额外的硬件。



      以下为原文

    Yes, but you might need extra hardware.

当Vdd是Rf时，测量一个已知的输入，然后可以从已知的VDIN计算VDD。



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    Measure a know input while Vdd is the ref. You can then calculate Vdd from the known Vinput

一般来说，假设你有一个引用，用Vdd来测量它作为所选的引用。明确地？这取决于你计划使用的实际情况。



      以下为原文

    In general: Assuming you have a reference, measure it with Vdd as the selected reference.
Specifically ? Depends on the actual heck you plan on using.

在没有任何特殊连接的情况下，有可能得到有意义的结果。你忘了告诉我们你在用什么PIC。（你确实知道有大约百万张照片，对吧？）我不想告诉你们，并不是所有的人都有相同的功能和特征。无论如何，这里有一种方法可能是相关的，或者也许不是，这取决于你的照片和你的要求。我经常使用这一点。将AD+加上参考集设置为AVdd，并将参考集设置为AVSSATA ADC通道，读取Vbg（带隙基准电压）。设置带隙基准，使ADC能够正常工作。读取ADC值。例如，10位ADC格式，您可以在Vbg插入VADC。E公式VADC=（ADC读取/ 1024）*AVDD并求解AVDD：AVDD＝VBG＊1024 /（ADC Read），如果您只是测试以查看AVDD在一定范围内，则不必计算程序中的值；只需计算对应于最小和/或最大可接受的ADC读数。AVDD的值，并比较ADC读取的值。计算这些离线，而不是在程序本身。程序只是将ADC读数的值与最小和最大可接受值进行比较。ADC读数＝VBG＊1024 /AVDD例如：我的PIC24FJ1024GB610具有VBG＝1.2伏+ 5%假设我们要验证AVdd等于3.3伏特+-5%标称ADC读数＝1.2×1024 / 3.3＝（大约）32MAX可接受ADC读数＝（1.2×1.05）* 1024 /（3.3 * 0.95）＝（大约）412min接受。ADC读取=（1.2×0.95）×1024（/ 3.3×1.05）=（大约）37A从我的测试程序中摘录如下：结果：VBG读数＝73BaseLoad：漂亮DAN接近这个特定测试的名义，但不要忘记公差。在这种情况下，不可排除标称的+- 10%的读数。如果需要更高精度，请使用外部参考电压源并将其连接到PIC的模拟输入之一。程序和计算是一样的，关于戴夫



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    It may be possible to get meaningful results without any special hookup.  You forgot to tell us what PIC you are using.  (You do know that there are about a gazillion PICs, right?  I hate to tell you that not all of them have the same functions and features.)

Anyhow, here's one approach that may be relevant, or, maybe not, depending on your PIC and your requirements.  I have used this from time to time.

• Set up the ADC with +Reference set to AVdd, and -Reference set to AVss
  
• Set up ADC channel to read Vbg (the Bandgap Reference voltage).
  
• Set up BandGap reference to be enabled for ADC.
  
• Read the ADC value.
  

For, say, a 10-bit ADC format, you can plug in Vbg for Vadc in the formula

    Vadc = (ADC Reading / 1024) * AVdd

And solve for AVdd:

   AVdd = Vbg * 1024 / (ADC Reading)

If you are just testing to see that AVdd is within a certain range, you don't have to calculate the value in your program; just calculate ADC readings corresponding to minimum and/or maximum acceptable values of AVdd and compare the value read by the ADC.  Calculate these off-line, not in the program itself.  The program just compares value from ADC reading with minimum and maximum acceptable values.

   ADC reading = Vbg * 1024 / AVdd

For example: My PIC24FJ1024GB610 has Vbg = 1.2 Volts +-5%

Suppose we want to verify that AVdd is equal to 3.3 Volts +- 5%

• Nominal ADC reading        =    1.2    * 1024 /    3.3     = (Approximately)372
  
• Max acceptable ADC Reading = (1.2*1.05)* 1024 / (3.3*0.95) = (Approximately)412
  
• Min acceptable ADC Reading = (1.2*0.95)* 1024 / (3.3*1.05) = (Approximately)337
  

A snippet from my test program looks like this:

    // Set up your ADC to be ready to read
    // ADC +ref is AVdd, ADC -ref is AVss
    ADC_SetConfiguration(ADC_CONFIGURATION_DEFAULT);

    // Make sure BandGap reference is turned on for A/D
    // For the VBG channel, this sets AD1CON5bits.BREQ to 1
    // For the 'GB610, AEDC_CHANNEL_FBG is 0x1C
    // For ADC channels connected to input pins, makes sure they
    // are set for analog mode
    ADC_ChannelEnable(ADC_CHANNEL_VBG);

    // Perform the conversion for the indicated channel
    int16_t adc_reading = ADC_Read10bit(ADC_CHANNEL_VBG);
    printf("Vbg reading = %dn", adc_reading);


Result:
Vbg reading = 373


Bottom line: Pretty dang close to nominal for this particular test, but don't forget about tolerances.  In this case readings of +-10% of nominal can't be excluded.  If you require more precision, use an external reference voltage source and connect it to one of the PIC's analog inputs.  The procedure and the calculations are the same.


Regards,

Dave

你可以使用一个LDO，比如微芯片MCP1700或MCP1702，它对VDD有0.4%的典型容差。否则，可以使用内部引用（如上文所述）来测量Vdd。即使电源被精确地指定，这仍然是一个好主意，以验证它是“在球场上”。



      以下为原文

    You could use an LDO such as the Microchip MCP1700 or MCP1702, which have typical tolerance of 0.4%, for the Vdd. Otherwise, you can use an internal reference, as described above, to measure Vdd. That is still a good idea even if the power supply is specified accurately, to verify that it is "in the ballpark".

不确定我的问题和答案，但是我的答案是肯定的。你想用万用表测量一下吗？或者你想和PIC自己一起参加奥运会吗？



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    Not sure if i udnersand the question, but my answer is yes. 

Do you want to just measure it once with a multimeter? or do you want to meaure Vcc ongoign with the pic itself

Volker，根据你的照片，答案会非常不同……阅读的准确性是什么？当做



      以下为原文

    Volker,
 
Depending of your PIC the answer will be very different...
What is the accuracy needed for reading ?
 
Regards

您好，谢谢您的回答和抱歉我的问题不准确。我有一个固定的设计与PIC24FJ256GB210。现在我必须测试，如果VCC（3，3V）在2，5V的边缘以上，我做进一步的事情。



      以下为原文

    Hello,
 
thanks for the answers and sorry for my inaccurate question.
 
I have a fixed design with a PIC24FJ256GB210.
 
Now i have to test if the vcc (3,3V) is above an edge of 2,5V before i do something further.
 
 

如上所述，你可能需要一些外部参考。MCU确实有一个“低电压检测”中断，但它更多的是用于监控内部电压调节器（用于核心），但这可能不是你想要的——你似乎想要检测上升的电压而不是下降的电压，并且触发的电压与你的电压不同。这是在停电期间还是正常运行期间？它需要多快的反应和速度有多快的VCC预期改变？这是真的Vcc为MCU你想监视或电压被馈送到其他设备？苏珊



      以下为原文

    As mentioned above you probably need some external reference. That MCU does have a 'low voltage detect' interrupt but it is more for monitoring when the internal voltage regulator (for the core) but that is probably not what you want - you seem to want to detect a rising voltage rather than a falling one and triggers on a different voltage than the one you mention.
Is this during power-up only or during normal operation? How fast does it need to react and how fast is the Vcc expected to change?
And is it really Vcc for the MCU you are wanting to monitor or the voltage being fed to some other device?
Susan

@沃尔克，PIC24FJ256GB210具有内部带隙电压基准。它有一个典型的1200毫伏的电压，因为Microchip没有公布PIC24FJ256GB210的数据表，它指定了基准可以拥有的最小和最大电压，并且仍然作为一个“好”的设备被传送。RNAL带隙电压基准。我在PIC24FJ系列中搜索了我手上的数据页的PDF。在具有内部带隙电压基准规范的那些中，典型值为1200毫伏，并且具有完整规范的那些显示最小1140MV和最大1260MV。我希望PIC24FJ256GB210具有相同的范围。您需要联系微芯片并获得PIC24FJ256GB210的完整规范的确认。取决于您的VDD离您的条件有多大，在您必须声明您的条件之前，您可以使用内部带GA。P电压参考，使你的测量。



      以下为原文

    @Volker,
 
The PIC24FJ256GB210 has an internal band gap voltage reference. It has a typical voltage of 1200mV.
 
A problem occurs because Microchip has not published a data sheet for the PIC24FJ256GB210 that specifies the minimum and maximum voltage the reference can have and still be shipped as a "good" device.
 
Other controllers have a complete specification for for the internal band gap voltage reference.
 
I have search the PDFs of the data sheets I have on hand for parts in the PIC24FJ family. Of those that have an internal band gap voltage reference specification the typical value is 1200mV, and those with a complete specification show a minimum of 1140mV and a maximum of 1260mV. I would expect the PIC24FJ256GB210 to have this same range.
 
You need to contact Microchip and get a confirmation of the complete specification for the PIC24FJ256GB210.
 
Depending on how close your VDD can be to 2.5 volts before you must assert your condition you may be able to use the internal band gap voltage reference to make your measurement.

你好，谢谢大家的帮助！



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    Hello,
 
thanks all for the help!

这些线程可能会有帮助：http://www. McCys.com /论坛/ M938933 .ASPX第932833号http://www. MICROCHOC.CO./RUM/M358981.ASPX第813047页。



      以下为原文

    These threads might be helpful:
  http://www.microchip.com/forums/m932833.aspx#932833
  http://www.microchip.com/.rums/m358981.aspx#813047