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doc: analogRead must not be called to frequently when WiFi is on #7981

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Apr 14, 2021
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doc: analogRead must not be called to frequently when WiFi is on #7981

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7 changes: 6 additions & 1 deletion doc/reference.rst
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Expand Up @@ -74,12 +74,17 @@ pin, except GPIO16. Standard Arduino interrupt types are supported:
Analog input
------------

**NOTE:**
Calling ``analogRead()`` too frequently causes WiFi to stop working. When
WiFi is under operation, ``analogRead()`` result may be cached for at least
5ms between effective calls.

ESP8266 has a single ADC channel available to users. It may be used
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 of bare ESP8266 is 0 — 1.0V, however some many
Input voltage range of bare ESP8266 is 0 — 1.0V, however some
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.
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