113 lines
5.5 KiB
HTML
113 lines
5.5 KiB
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<p><strong>Reference</strong> <a class='wikilink' href='index.html'>Language</a> (<a class='wikilink' href='Extended.html'>extended</a>) | <a class='wikilink' href='Libraries.html'>Libraries</a> | <a class='wikilink' href='Comparison.html'>Comparison</a>
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</p>
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<p class='vspace'></p><h2>analogWrite()</h2>
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<h4>Description</h4>
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<p>Writes an analog value (<a class='wikilink' href='http://arduino.cc/en/Tutorial/PWM'>PWM wave</a>) to a pin. Can be used to light a LED at varying brightnesses or drive a motor at various speeds. After a call to <strong>analogWrite()</strong>, the pin will generate a steady square wave of the specified duty cycle until the next call to <strong>analogWrite()</strong> (or a call to <strong>digitalRead()</strong> or <strong>digitalWrite()</strong> on the same pin). The frequency of the PWM signal is approximately 490 Hz.
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</p>
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<p class='vspace'></p><p>On newer Arduino boards (including the Mini and BT) with the <span class='wikiword'>ATmega168</span> chip, this function works on pins 3, 5, 6, 9, 10, and 11. Older USB and serial Arduino boards with an <span class='wikiword'>ATmega8</span> only support analogWrite() on pins 9, 10, and 11.
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</p>
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<p class='vspace'></p><h4>Syntax</h4>
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<p>analogWrite(pin, value)
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</p>
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<p class='vspace'></p><h4>Parameters</h4>
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<p>pin: the pin to write to.
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</p>
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<p class='vspace'></p><p>value: the duty cycle: between 0 (always off) and 255 (always on).
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</p>
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<p class='vspace'></p><h4>Returns</h4>
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<p>nothing
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</p>
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<p class='vspace'></p><h4>Notes and Known Issues</h4>
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<p>You do not need to call pinMode() to set the pin as an output before calling analogWrite().
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</p>
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<p class='vspace'></p><p>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.
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</p>
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<p class='vspace'></p><h4>Example</h4>
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<p>Sets the output to the LED proportional to the value read from the potentiometer.
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</p>
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<p class='vspace'></p><pre>
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int ledPin = 9; // LED connected to digital pin 9
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int analogPin = 3; // potentiometer connected to analog pin 3
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int val = 0; // variable to store the read value
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void setup()
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{
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pinMode(ledPin, OUTPUT); // sets the pin as output
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}
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void loop()
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{
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val = analogRead(analogPin); // read the input pin
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analogWrite(ledPin, val / 4); // analogRead values go from 0 to 1023, analogWrite values from 0 to 255
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}
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</pre>
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<p class='vspace'></p><h4>See also</h4>
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<ul><li><a class='wikilink' href='AnalogRead.html'>analogRead</a>()
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</li><li><a class='wikilink' href='http://arduino.cc/en/Tutorial/PWM'>Tutorial: PWM</a>
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</li><li><a class='urllink' href='http://www.arduino.cc/playground/Main/TimerPWMCheatsheet' rel='nofollow'>Adjusting Arduino PWM Frequencies</a>
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</li></ul><p class='vspace'></p><p><a class='wikilink' href='index.html'>Reference Home</a>
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<p class='vspace'></p><p><em>Corrections, suggestions, and new documentation should be posted to the <a class='urllink' href='http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?board=swbugs' rel='nofollow'>Forum</a>.</em>
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</p>
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<p class='vspace'></p><p>The text of the Arduino reference is licensed under a
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<a class='urllink' href='http://creativecommons.org/licenses/by-sa/3.0/' rel='nofollow'>Creative Commons Attribution-ShareAlike 3.0 License</a>. Code samples in the reference are released into the public domain.
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