Add content Functions/Analog IO

Author: Akshay Sharma

Language/Functions/Analog IO/analogRead.adoc

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+:source-highlighter: pygments
+:pygments-style: arduino
+:ext-relative: adoc
+
+
+= analogRead()
+
+
+// OVERVIEW SECTION STARTS
+[#overview]
+--
+
+[float]
+=== Description
+Reads the value from the specified analog pin. The Arduino board contains a 6 channel (8 channels on the Mini and Nano, 16 on the Mega), 10-bit analog to digital converter. This means that it will map input voltages between 0 and 5 volts into integer values between 0 and 1023. This yields a resolution between readings of: 5 volts / 1024 units or, .0049 volts (4.9 mV) per unit. The input range and resolution can be changed using link:analogReference{ext-relative}[analogReference()]`.
+
+It takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.
+[%hardbreaks]
+
+
+[float]
+=== Syntax
+
+`analogRead(pin)`
+
+[float]
+=== Parameters
+`pin`: the number of the analog input pin to read from (0 to 5 on most boards, 0 to 7 on the Mini and Nano, 0 to 15 on the Mega)
+
+[float]
+=== Returns
+int(0 to 1023)
+
+--
+// OVERVIEW SECTION ENDS
+
+
+
+
+// HOW TO USE SECTION STARTS
+[#howtouse]
+--
+
+[float]
+=== Example Code
+// Describe what the example code is all about and add relevant code   ►►►►► THIS SECTION IS MANDATORY ◄◄◄◄◄
+The code reads the voltage on analogPin and displays it.
+
+[source,arduino]
+----
+int analogPin = 3;     // potentiometer wiper (middle terminal) connected to analog pin 3
+                       // outside leads to ground and +5V
+int val = 0;           // variable to store the value read
+
+void setup()
+{
+  Serial.begin(9600);              //  setup serial
+}
+
+void loop()
+{
+  val = analogRead(analogPin);     // read the input pin
+  Serial.println(val);             // debug value
+}
+----
+[%hardbreaks]
+
+[float]
+=== Notes and Warnings
+If the analog input pin is not connected to anything, the value returned by analogRead() will fluctuate based on a number of factors (e.g. the values of the other analog inputs, how close your hand is to the board, etc.).
+[%hardbreaks]
+
+[float]
+=== See also
+// Link relevant content by category, such as other Reference terms (please add the tag #LANGUAGE#),
+// definitions (please add the tag #DEFINITION#), and examples of Projects and Tutorials
+// (please add the tag #EXAMPLE#)  ►►►►► THIS SECTION IS MANDATORY ◄◄◄◄◄
+
+[role="language"]
+* #LANGUAGE# link:analogReference{ext-relative}[analogreference()] +
+* #LANGUAGE# link:analogReadResolution{ext-relative}[analogReadResolution()] +
+* #LANGUAGE# (http://arduino.cc/en/Tutorial/AnalogInputPins[Tutorial: Analog Input Pins])
+
+
+--
+// HOW TO USE SECTION ENDS

Language/Functions/Analog IO/analogReference.adoc

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+:source-highlighter: pygments
+:pygments-style: arduino
+//:ext-relative: adoc
+
+
+= analogReference()
+
+
+// OVERVIEW SECTION STARTS
+[#overview]
+--
+
+[float]
+=== 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 (not available on the Arduino Mega)
+* INTERNAL1V1: a built-in 1.1V reference (Arduino Mega only)
+* INTERNAL2V56: a built-in 2.56V reference (Arduino Mega only)
+* EXTERNAL: the voltage applied to the AREF pin (0 to 5V only) is used as the reference.
+[%hardbreaks]
+
+
+[float]
+=== Syntax
+`analogReference(type)`
+
+
+[float]
+=== Parameters
+`type`: which type of reference to use (DEFAULT, INTERNAL, INTERNAL1V1, INTERNAL2V56, or EXTERNAL).
+
+[float]
+=== Returns
+Nothing
+
+--
+// OVERVIEW SECTION ENDS
+
+
+
+
+// HOW TO USE SECTION STARTS
+[#howtouse]
+--
+
+[float]
+=== Notes and Warnings
+After changing the analog reference, the first few readings from `analogRead()` may not be accurate.
+
+*Don't use anything less than 0V or more than 5V for external reference voltage on the AREF pin! If you're using an external reference on 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.
+[%hardbreaks]
+
+[float]
+=== See also
+// Link relevant content by category, such as other Reference terms (please add the tag #LANGUAGE#),
+// definitions (please add the tag #DEFINITION#), and examples of Projects and Tutorials
+// (please add the tag #EXAMPLE#)  ►►►►► THIS SECTON IS MANDATORY ◄◄◄◄◄
+
+[role="example"]
+* #EXAMPLE# http://arduino.cc/en/Tutorial/AnalogInputPins[Description of analog input pins]
+
+[role="language"]
+* #LANGUAGE# link:analogRead{ext-relative}[analogRead()]
+
+--
+// HOW TO USE SECTION ENDS