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Analog input voltage can be 3.3V (#5020)

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* Analog input voltage can be 3.3V

According to this tutorial and my personal test with my Amica, 1.0V delivers 320 and 3.3V delivers 1024 at 10-bit resolution. I guess 3.3V is possible.

* Update reference.rst

Added warnings.

* Update reference.rst

* Update reference.rst

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SarenT 2018-08-14 03:53:39 +02:00 committed by Develo
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doc/reference.rst
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@ -42,7 +42,12 @@ either to read voltage at ADC pin, or to read module supply voltage
(VCC).
To read external voltage applied to ADC pin, use ``analogRead(A0)``.
Input voltage range is 0 — 1.0V.
Input voltage range of bare ESP8266 is 0 — 1.0V, however some many
boards may implement voltage dividers. To be on the safe side, <1.0V
can be tested. If e.g. 0.5V delivers values around ~512, then maximum
voltage is very likely to be 1.0V and 3.3V may harm the ESP8266.
However values around ~150 indicates that the maximum voltage is
likely to be 3.3V.
To read VCC voltage, use ``ESP.getVcc()`` and ADC pin must be kept
unconnected. Additionally, the following line has to be added to the