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ANALOG READ:
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 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.
Syntax: analogRead(pin)
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)
- Returns: int (0 to 1023)
“Note: 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.).”
ANALOG WRITE:
Writes an analog value (PWM wave) to a pin. Can be used to light a LED at varying brightness or drive a motor at various speeds. After a call to analogWrite(), the pin will generate a steady square wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite() on the same pin). The frequency of the PWM signal on most pins is approximately 490 Hz. On the Uno and similar boards, pins 5 and 6 have a frequency of approximately 980 Hz. Pins 3 and 11 on the Leonardo also run at 980 Hz. On most Arduino boards (those with the ATmega168 or ATmega328), this function works on pins 3, 5, 6, 9, 10, and 11. On the Arduino Mega, it works on pins 2 – 13 and 44 – 46. Older Arduino boards with an ATmega8 only support analogWrite() on pins 9, 10, and 11. The Arduino Due supports analogWrite() on pins 2 through 13, plus pins DAC0 and DAC1. Unlike the PWM pins, DAC0 and DAC1 are Digital to Analog converters, and act as true analog outputs.
“Note: You do not need to call pinMode() to set the pin as an output before calling analogWrite().“
The analogWrite function has nothing to do with the analog pins or the analogRead function.
Syntax: analogWrite(pin, value)
Parameters:
- Pin: The pin to write to.
- Value: The duty cycle: between 0 (always off) and 255 (always on).
- Returns: Nothing.
ANALOG REFERENCE:
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.
Syntax: analogReference(type)
Parameters:
- Type: which type of reference to use (DEFAULT, INTERNAL, INTERNAL1V1, INTERNAL2V56, or EXTERNAL).
- Returns: None.
“Note: After changing the analog reference, the first few readings from analogRead() may not be accurate.”