Arduino平臺的設(shè)計非常靈活，使用Uno等單個開發(fā)板就可以創(chuàng)建出無數(shù)項目。但是，專為執(zhí)行特定任務(wù)而設(shè)計的專用板對某些項目來說尤其有用。為了展示這一點，我們將用LilyPad MP3（一種變體Arduino開發(fā)板）來構(gòu)建一個音板。

變體開發(fā)板的工作原理

開源軟件平臺允許開發(fā)人員檢查和修改他們的代碼。同樣，像Arduino這樣的開源硬件平臺允許第三方構(gòu)建他們自己版本的兼容板。Arduino板的LilyPad系列就是這樣的一種變體。該板專為電子紡織品設(shè)計，可以縫制到織物項目中。這使其成為服裝和智能服裝的理想選擇。

LilyPad MP3是LilyPad系列的另一個子變體，包括一個內(nèi)置SD卡讀卡器、一個立體聲音頻放大器和3.5毫米耳機插孔，以及五個預(yù)編程過的觸發(fā)器輸入。無需任何編碼設(shè)置，您最多可以連接五個觸發(fā)器來播放預(yù)先錄制的聲音文件。如果您曾在迪士尼見過可以播放一組預(yù)先編寫好的語句的星球大戰(zhàn)沖鋒隊 ，那么可以告訴您LilyPad MP3的功能與其非常相似。

雖然LilyPad MP3可以像任何Arduino板那樣編程，但是該項目的優(yōu)點是您可以在不修改任何現(xiàn)有代碼的情況下對音板進行設(shè)置。它可以向您證明為您的項目盡早選擇合適的開發(fā)板有多么值得。使用普通的Arduino Uno需要有一個外部擴展板才能具有與LilyPad MP3相同的功能，而且體積會更大。由于大多數(shù)Arduino板都可以與大部分草圖兼容，因此找到滿足您需求的外形尺寸可以為您省去大量的時間和麻煩。

所需組件

對于本項目，我們將演示LilyPad MP3如何在面包板上工作的，其實就是讓線路能夠正常工作。首先，您需要一個LilyPad MP3。

您還需要1-5個按鈕（只需要一個，但是LilyPad最多支持5個）、一個揚聲器（或耳機）和3.5毫米電纜。

由于LilyPad旨在用于服裝，您可以選擇使用一些線和針將設(shè)備縫制到外套、衣服或任何其他您想要裝上音板的地方。使用導(dǎo)電布線可以讓您將電線直接編織到衣服的面料中。

代碼

如上所述，LilyPad MP3上默認觸發(fā)器草圖的代碼預(yù)裝在了每塊板上。您不需要上傳此文件，但查看這些代碼來了解工作原理會很有幫助。

// “Trigger” example sketch for Lilypad MP3 Player
// Mike Grusin, SparkFun Electronics
// http://www.sparkfun.com

// This sketch (which is preloaded onto the board by default),
// will play a specific audio file when one of the five trigger
// inputs (labeled T1 – T5) is momentarily grounded.

// You can place up to five audio files on the micro-SD card.
// These files should have the desired trigger number (1 to 5)
// as the first character in the filename. The rest of the
// filename can be anything you like. Long file names will work,
// but will be translated into short 8.3 names. We recommend using
// 8.3 format names without spaces, but the following characters
// are OK: .$%’-_@~`!(){}^#&. The VS1053 can play a variety of
// audio formats, see the datasheet for information.

// By default, a new trigger will interrupt a playing file, except
// itself. (In other words, a new trigger won’t restart an
// already-playing file). You can easily change this behavior by
// modifying the global variables “interrupt” and “interruptself”
// below.

// This sketch can output serial debugging information if desired
// by changing the global variable “debugging” to true. Note that
// this will take away trigger inputs 4 and 5, which are shared
// with the TX and RX lines. You can keep these lines connected to
// trigger switches and use the serial port as long as the triggers
// are normally open (not grounded) and remain ungrounded while the
// serial port is in use.

// Uses the SdFat library by William Greiman, which is supplied
// with this archive, or download from http://code.google.com/p/sdfatlib/

// Uses the SFEMP3Shield library by Bill Porter, which is supplied
// with this archive, or download from http://www.billporter.info/

// License:
// We use the “beerware” license for our firmware. You can do
// ANYTHING you want with this code. If you like it, and we meet
// someday, you can, but are under no obligation to, buy me a
// (root) beer in return.

// Have fun!
// -your friends at SparkFun

// Revision history:
// 1.0 initial release MDG 2012/11/01

// We’ll need a few libraries to access all this hardware!

#include // To talk to the SD card and MP3 chip
#include // SD card file system
#include // MP3 decoder chip

// Constants for the trigger input pins, which we’ll place
// in an array for convenience:

const int TRIG1 = A0;
const int TRIG2 = A4;
const int TRIG3 = A5;
const int TRIG4 = 1;
const int TRIG5 = 0;
int trigger[5] = {TRIG1, TRIG2, TRIG3, TRIG4, TRIG5};

// And a few outputs we’ll be using:

const int ROT_LEDR = 10; // Red LED in rotary encoder (optional)
const int EN_GPIO1 = A2; // Amp enable + MIDI/MP3 mode select
const int SD_CS = 9; // Chip Select for SD card

// Create library objects:

SFEMP3Shield MP3player;
SdFat sd;

// Set debugging = true if you’d like status messages sent
// to the serial port. Note that this will take over trigger
// inputs 4 and 5. (You can leave triggers connected to 4 and 5
// and still use the serial port, as long as you’re careful to
// NOT ground the triggers while you’re using the serial port).

boolean debugging = false;

// Set interrupt = false if you would like a triggered file to
// play all the way to the end. If this is set to true, new
// triggers will stop the playing file and start a new one.

boolean interrupt = true;

// Set interruptself = true if you want the above rule to also
// apply to the same trigger. In other words, if interrupt = true
// and interruptself = false, subsequent triggers on the same
// file will NOT start the file over. However, a different trigger
// WILL stop the original file and start a new one.

boolean interruptself = false;

// We’ll store the five filenames as arrays of characters.
// “Short” (8.3) filenames are used, followed by a null character.

char filename[5][13];

void setup()
{
int x, index;
SdFile file;
byte result;
char tempfilename[13];

// Set the five trigger pins as inputs, and turn on the
// internal pullup resistors:

for (x = 0; x <= 4; x++) { pinMode(trigger[x], INPUT); digitalWrite(trigger[x], HIGH); } // If serial port debugging is inconvenient, you can connect // a LED to the red channel of the rotary encoder to blink // startup error codes: pinMode(ROT_LEDR, OUTPUT); digitalWrite(ROT_LEDR, HIGH); // HIGH = off // The board uses a single I/O pin to select the // mode the MP3 chip will start up in (MP3 or MIDI), // and to enable/disable the amplifier chip: pinMode(EN_GPIO1, OUTPUT); digitalWrite(EN_GPIO1, LOW); // MP3 mode / amp off // If debugging is true, initialize the serial port: // (The ‘F’ stores constant strings in flash memory to save RAM) if (debugging) { Serial.begin(9600); Serial.println(F(“Lilypad MP3 Player trigger sketch”)); } // Initialize the SD card; SS = pin 9, half speed at first if (debugging) Serial.print(F(“initialize SD card… “)); result = sd.begin(SD_CS, SPI_HALF_SPEED); // 1 for success if (result != 1) // Problem initializing the SD card { if (debugging) Serial.print(F(“error, halting”)); errorBlink(1); // Halt forever, blink LED if present. } else if (debugging) Serial.println(F(“success!”)); // Start up the MP3 library if (debugging) Serial.print(F(“initialize MP3 chip… “)); result = MP3player.begin(); // 0 or 6 for success // Check the result, see the library readme for error codes. if ((result != 0) && (result != 6)) // Problem starting up { if (debugging) { Serial.print(F(“error code “)); Serial.print(result); Serial.print(F(“, halting.”)); } errorBlink(result); // Halt forever, blink red LED if present. } else if (debugging) Serial.println(F(“success!”)); // Now we’ll access the SD card to look for any (audio) files // starting with the characters ‘1’ to ‘5’: if (debugging) Serial.println(F(“reading root directory”)); // Start at the first file in root and step through all of them: sd.chdir(“/”, true); while (file.openNext(sd.vwd(), O_READ)) { // get filename file.getFilename(tempfilename); // Does the filename start with char ‘1’ through ‘5’? if (tempfilename[0] >= ‘1’ && tempfilename[0] <= ‘5’)
{
// Yes! subtract char ‘1’ to get an index of 0 through 4.

index = tempfilename[0] – ‘1’;

// Copy the data to our filename array.

strcpy(filename[index], tempfilename);

if (debugging) // Print out file number and name
{
Serial.print(F(“found a file with a leading “));
Serial.print(index + 1);
Serial.print(F(“: “));
Serial.println(filename[index]);
}
}
else if (debugging)
{
Serial.print(F(“found a file w/o a leading number: “));
Serial.println(tempfilename);
}

file.close();
}

if (debugging)
Serial.println(F(“done reading root directory”));

if (debugging) // List all the files we saved:
{
for(x = 0; x <= 4; x++)
{
Serial.print(F(“trigger “));
Serial.print(x + 1);
Serial.print(F(“: “));
Serial.println(filename[x]);
}
}

// Set the VS1053 volume. 0 is loudest, 255 is lowest (off):

MP3player.setVolume(10, 10);

// Turn on the amplifier chip:

digitalWrite(EN_GPIO1, HIGH);
delay(2);
}

void loop()
{
int t; // current trigger
static int last_t; // previous (playing) trigger
int x;
byte result;

// Step through the trigger inputs, looking for LOW signals.
// The internal pullup resistors will keep them HIGH when
// there is no connection to the input.

// If serial debugging is on, only check triggers 1-3,
// otherwise check triggers 1-5.

for(t = 1; t <= (debugging ? 3 : 5); t++)
{
// The trigger pins are stored in the inputs[] array.
// Read the pin and check if it is LOW (triggered).

if (digitalRead(trigger[t – 1]) == LOW)
{
// Wait for trigger to return high for a solid 50ms
// (necessary to avoid switch bounce on T2 and T3
// since we need those free for I2C control of the
// amplifier)

x = 0;
while(x < 50)
{
if (digitalRead(trigger[t – 1]) == HIGH)
x++;
else
x = 0;
delay(1);
}

if (debugging)
{
Serial.print(F(“got trigger “));
Serial.println(t);
}

// Do we have a valid filename for this trigger?
// (Invalid filenames will have 0 as the first character)

if (filename[t – 1][0] == 0)
{
if (debugging)
Serial.println(F(“no file with that number”));
}
else // We do have a filename for this trigger!
{
// If a file is already playing, and we’ve chosen to
// allow playback to be interrupted by a new trigger,
// stop the playback before playing the new file.

if (interrupt && MP3player.isPlaying() && ((t != last_t) || interruptself))
{
if (debugging)
Serial.println(F(“stopping playback”));

MP3player.stopTrack();
}

// Play the filename associated with the trigger number.
// (If a file is already playing, this command will fail
// with error #2).

result = MP3player.playMP3(filename[t – 1]);

if (result == 0) last_t = t; // Save playing trigger

if(debugging)
{
if(result != 0)
{
Serial.print(F(“error “));
Serial.print(result);
Serial.print(F(” when trying to play track “));
}
else
{
Serial.print(F(“playing “));
}
Serial.println(filename[t – 1]);
}
}
}
}
}

void errorBlink(int blinks)
{
// The following function will blink the red LED in the rotary
// encoder (optional) a given number of times and repeat forever.
// This is so you can see any startup error codes without having
// to use the serial monitor window.

int x;

while(true) // Loop forever
{
for (x = 0; x < blinks; x++) // Blink the given number of times
{
digitalWrite(ROT_LEDR, LOW); // Turn LED ON
delay(250);
digitalWrite(ROT_LEDR, HIGH); // Turn LED OFF
delay(250);
}
delay(1500); // Longer pause between blink-groups
}
}

雖然逐行看下來代碼實在太多了（而且很多都在本項目中用不到），但是有幾個關(guān)鍵點值得強調(diào)。首先，有一些函數(shù)是Bill Porter的MP3播放器庫的一部分。這些函數(shù)通過VS1053B解碼芯片控制音頻文件。這些獨特的函數(shù)包括：

● setVolume(): 該函數(shù)可以調(diào)節(jié)輸出音量的級別。
● isPlaying(): 該函數(shù)可用于確定當前是否正在播放MP3（可用于中斷或停止播放）。
● stopTrack(): 可以停止當前正在播放的曲目。
● playMP3(): 該函數(shù)用于播放SD卡中的文件。默認草圖設(shè)置為播放與輸入所連接觸發(fā)器匹配的文件。

要在LilyPad上設(shè)置音軌，您最多可以將五個音頻文件添加到微SD卡中。盡管LilyPad的名稱是MP3，但是它支持多種音頻文件格式。您可以在此處找到所支持的格式列表。您可以隨意命名文件，只要文件名以1到5之間的數(shù)字開頭即可。

默認草圖將播放與激活的觸發(fā)器對應(yīng)的音頻文件。觸發(fā)器1（在LilyPad上標記為T1）將激活以1開頭的音頻文件。觸發(fā)器2將播放以2開頭的文件，以此類推。只要您正確命名音頻文件，就不必對代碼進行任何處理。

接線

將所有組件連接到LilyPad很簡單。將微SD卡插入微SD卡槽，然后將揚聲器或一副耳機插入耳機插孔。如果您想將揚聲器直接連接到開發(fā)板，LilyPad還具有用于左右揚聲器的正負極觸點。

接下來，將按鈕連接到您要使用的每個觸發(fā)器。按鈕的一側(cè)連接到GND，而另一側(cè)連接到您要激活的觸發(fā)器觸點。LilyPad上的觸發(fā)器觸點中有一個大圓形觸點和一個緊鄰大觸點的較小觸點。您可以將電線焊接到較小的觸點，或?qū)㈦娋€纏繞在較大的觸點上。

按下按鈕，此時應(yīng)該會觸發(fā)音頻文件的播放。確認接線正常后，您就可以嘗試使用導(dǎo)電布線將接線縫入織物中了。

這篇文章來源于DevicePlus.com英語網(wǎng)站的翻譯稿。

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