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.. _arduino-analogwrite:
analogWrite()
=============
TODO
In libmaple, analogWrite is just a convenience alias for
:ref:`pwmWrite`. This is because PWM is not true analog output (i.e.,
is not the output of a DAC), so the name was badly-chosen; however,
for the sake of compatibility, the alias was provided.
.. doxygenfunction:: pwmWrite
Description
-----------
Writes an analog value
(`PWM wave <http://arduino.cc/en/Tutorial/PWM>`_) to a pin. Can be
used to light a LED at varying brightnesses 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 is approximately 490 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 through 13. Older Arduino boards with an
ATmega8 only support analogWrite() on pins 9, 10, and 11. You do
not need to call pinMode() to set the pin as an output before
calling analogWrite().
The *analogWrite* function has nothing whatsoever 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
Notes and Known Issues
----------------------
The PWM outputs generated on pins 5 and 6 will have
higher-than-expected duty cycles. This is because of interactions
with the millis() and delay() functions, which share the same
internal timer used to generate those PWM outputs. This will be
noticed mostly on low duty-cycle settings (e.g 0 - 10) and may
result in a value of 0 not fully turning off the output on pins 5
and 6.
Example
-------
Sets the output to the LED proportional to the value read from the
potentiometer.
::
int ledPin = 9; // LED connected to digital pin 9
int analogPin = 3; // potentiometer connected to analog pin 3
int val = 0; // variable to store the read value
void setup()
{
pinMode(ledPin, OUTPUT); // sets the pin as output
}
void loop()
{
val = analogRead(analogPin); // read the input pin
analogWrite(ledPin, val / 4); // analogRead values go from 0 to 1023, analogWrite values from 0 to 255
}
See also
--------
- `analogRead <http://arduino.cc/en/Reference/AnalogRead>`_\ ()
- `Tutorial: PWM <http://arduino.cc/en/Tutorial/PWM>`_
|
