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+.. _arduino-analogreference:
+
+analogReference(type)
+=====================
+
+Description
+-----------
+
+Configures the reference voltage used for analog input (i.e. the
+value used as the top of the input range). The options are:
+
+
+
+
+-  DEFAULT: the default analog reference of 5 volts (on 5V Arduino
+   boards) or 3.3 volts (on 3.3V Arduino boards)
+-  INTERNAL: an built-in reference, equal to 1.1 volts on the
+   ATmega168 or ATmega328 and 2.56 volts on the ATmega8.
+-  EXTERNAL: the voltage applied to the AREF pin is used as the
+   reference.
+
+
+
+Parameters
+----------
+
+type: which type of reference to use (DEFAULT, INTERNAL, or
+EXTERNAL).
+
+
+
+Returns
+-------
+
+None.
+
+
+
+Warning
+-------
+
+**If you're using an external reference voltage (applied to the AREF pin), you must set the analog reference to EXTERNAL before calling analogRead().**
+Otherwise, you will short together the active reference voltage
+(internally generated) and the AREF pin, possibly damaging the
+microcontroller on your Arduino board.
+
+
+
+Alternatively, you can connect the external reference voltage to
+the AREF pin through a 5K resistor, allowing you to switch between
+external and internal reference voltages. Note that the resistor
+will alter the voltage that gets used as the reference because
+there is an internal 32K resistor on the AREF pin. The two act as a
+voltage divider, so, for example, 2.5V applied through the resistor
+will yield 2.5 \* 32 / (32 + 5) = ~2.2V at the AREF pin.
+
+
+
+See also
+--------
+
+
+-  `Description of the analog input pins <http://arduino.cc/en/Tutorial/AnalogInputPins>`_
+-  `analogRead <http://arduino.cc/en/Reference/AnalogRead>`_\ ()
+
+