项目笔记：Arduino读取SD卡

1 硬件连接（使用Arduino Uno）：

CS -> 10
SCK -> 13
MOSI -> 11
MISO -> 12
VCC ->5V
GND -> GND

2 让Arduino检测到SD卡

官方测试程序：检测SD卡连接并输出卡型号

/*SD card testThis example shows how use the utility libraries on which the'SD library is based in order to get info about your SD card.Very useful for testing a card when you're not sure whether its working or not.The circuit:SD card attached to SPI bus as follows:** MOSI - pin 11 on Arduino Uno/Duemilanove/Diecimila** MISO - pin 12 on Arduino Uno/Duemilanove/Diecimila** CLK - pin 13 on Arduino Uno/Duemilanove/Diecimila** CS - depends on your SD card shield or module.Pin 4 used here for consistency with other Arduino examplescreated  28 Mar 2011by Limor Friedmodified 9 Apr 2012by Tom Igoe
*/
// include the SD library:
#include <SPI.h>
#include <SD.h>// set up variables using the SD utility library functions:
Sd2Card card;
SdVolume volume;
SdFile root;// change this to match your SD shield or module;
// Arduino Ethernet shield: pin 4
// Adafruit SD shields and modules: pin 10
// Sparkfun SD shield: pin 8
// MKRZero SD: SDCARD_SS_PIN
const int chipSelect = 4;void setup() {// Open serial communications and wait for port to open:Serial.begin(9600);while (!Serial) {; // wait for serial port to connect. Needed for native USB port only}Serial.print("\nInitializing SD card...");// we'll use the initialization code from the utility libraries// since we're just testing if the card is working!if (!card.init(SPI_HALF_SPEED, chipSelect)) {Serial.println("initialization failed. Things to check:");Serial.println("* is a card inserted?");Serial.println("* is your wiring correct?");Serial.println("* did you change the chipSelect pin to match your shield or module?");while (1);} else {Serial.println("Wiring is correct and a card is present.");}// print the type of cardSerial.println();Serial.print("Card type:         ");switch (card.type()) {case SD_CARD_TYPE_SD1:Serial.println("SD1");break;case SD_CARD_TYPE_SD2:Serial.println("SD2");break;case SD_CARD_TYPE_SDHC:Serial.println("SDHC");break;default:Serial.println("Unknown");}// Now we will try to open the 'volume'/'partition' - it should be FAT16 or FAT32if (!volume.init(card)) {Serial.println("Could not find FAT16/FAT32 partition.\nMake sure you've formatted the card");while (1);}Serial.print("Clusters:          ");Serial.println(volume.clusterCount());Serial.print("Blocks x Cluster:  ");Serial.println(volume.blocksPerCluster());Serial.print("Total Blocks:      ");Serial.println(volume.blocksPerCluster() * volume.clusterCount());Serial.println();// print the type and size of the first FAT-type volumeuint32_t volumesize;Serial.print("Volume type is:    FAT");Serial.println(volume.fatType(), DEC);volumesize = volume.blocksPerCluster();    // clusters are collections of blocksvolumesize *= volume.clusterCount();       // we'll have a lot of clustersvolumesize /= 2;                           // SD card blocks are always 512 bytes (2 blocks are 1KB)Serial.print("Volume size (Kb):  ");Serial.println(volumesize);Serial.print("Volume size (Mb):  ");volumesize /= 1024;Serial.println(volumesize);Serial.print("Volume size (Gb):  ");Serial.println((float)volumesize / 1024.0);Serial.println("\nFiles found on the card (name, date and size in bytes): ");root.openRoot(volume);// list all files in the card with date and sizeroot.ls(LS_R | LS_DATE | LS_SIZE);
}void loop(void) {}

如果测试失败，要注意以下操作：

1 Initializing failed:
确认接线：对于Arduino Uno，SD卡读卡器的CS引脚要连接4.
如果接线正确，确认chipSelect值也为4

2 Could not find FAT16/FAT32 partition.\nMake sure you’ve formatted the card：
这一步需要对SD卡进行格式化，一定要选择FAT16或FAT32格式。对于内存大于32G的SD卡，windows自带的格式化工具不会提供FAT32选项，因此需要借用第三方工具：
http://ridgecrop.co.uk/index.htm?guiformat.htm

测试成功结果如下

2 利用SD卡读写文件

#include <SD.h>
#include <SPI.h>const int chipSelect = 10;
String fileName = "test.txt";
File myFile;void setup() {// Open serial communications and wait for port to open:Serial.begin(9600);pinMode(chipSelect, OUTPUT);// wait for Serial Monitor to connect. Needed for native USB port boards only:while (!Serial);Serial.print("Initializing SD card...");if (!SD.begin(chipSelect)) {Serial.println("initialization failed. Things to check:");Serial.println("1. is a card inserted?");Serial.println("2. is your wiring correct?");Serial.println("3. did you change the chipSelect pin to match your shield or module?");Serial.println("Note: press reset button on the board and reopen this Serial Monitor after fixing your issue!");while (true);}Serial.println("initialization done.");// open the file. note that only one file can be open at a time,// so you have to close this one before opening another.myFile = SD.open(fileName, FILE_WRITE);// if the file opened okay, write to it:if (myFile) {Serial.print("Writing to test.txt...");myFile.println("testing 1, 2, 3.");if (SD.exists(fileName)) {Serial.println("file exists");}// close the file:myFile.close();Serial.println("done.");} else {// if the file didn't open, print an error:Serial.println("error opening test.txt");}Serial.println("reopening...");// re-open the file for reading:myFile = SD.open(fileName);if (myFile) {Serial.println(fileName + ":");// read from the file until there's nothing else in it:while (myFile.available()) {Serial.write(myFile.read());}// close the file:Serial.println("done.");myFile.close();} else {// if the file didn't open, print an error:Serial.println("error opening test.txt");}
}void loop() {// nothing happens after setup
}

里面调用的SD类方法：
1

SD.begin(chipSelect)

启动SD类，chipSelect为SD读卡器CS引脚连接的Arduino引脚。返回值为boolean，代表SD卡是否成功启动

SD.open(fileName, FILE_WRITE)

打开文件，参数为（文件名，读取方式）。注意文件名采用8.3格式，即文件名最多8字符，文件拓展名最多3字符，不区分大小写。如果文件名长度超过限制可能造成文件创建失败。

读取方式分为FILE_READ和FILE_WRITE，如果该参数不填默认为FILE_READ。在FILE_READ为只读状态，而FILE_WRITE允许修改文件。在FILE_WRITE状态下如果open的文件名不存在会创建新文件。

在FILE_READ模式下默认从文件头读取，在FILE_WRITE模式下默认从文件末尾读取

该方法返回值为一个文件（File类型），代表打开的文件。File类型支持被作为boolean，true代表存在文件，false代表不存在文件

SD.exists(fileName)

判断文件是否存在，返回boolean

文件操作方法：

myFile.println()

在文件里打印信息

myFile.close()

关闭并退出当前文件

上述测试程序运行结果：

注：我在测试中调用了程序多次，导致test.txt里面有多行内容。第一次运行后test.txt中只会有一行testing 1 2 3

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