针对硬件上的需求，我们开发了SD卡模块，它通过SPI接口与Arduino进行通信：

同时，为了方便同Arduino的SPI接口进行连接，提供了相应的IDC扩展板，该扩展板上有一个专门为SPI设计的六芯插座：

电路的连接上则依然沿用了电子积木所一向强调的即插即用方式，我们只需要用6芯的IDC连接线，将IDC扩展板上的SPI插座与SD卡模块上的相应插座连接起来，就完成了电路部分的连接：

回到软件部分，我们的目标是要让SD卡上记录的数据能够在电脑上顺利地读出，因此在向SD卡上记录相应数据的时候需要遵循一定的规定，即文件系统的类型。对于像Arduino这样的小系统来讲，相对简单的FAT16是一个比较不错的选择。

在这里我们要用到读卡器来对SD卡进行相应的处理，将其格式化成FAT文件系统：

Arduino上使用的软件则是基于SparkFun提供的FAT库，但根据硬件差异做了一定的修改，你可以从这里下载到修改过的FAT库。该库需要被解压缩到Arduino的hardware\libraries子目录中。

测试时使用的时FAT库里自带的示例程序：

//Include all the libraries necessary for FAT32
#include <byteordering.h>
#include <fat.h>
#include <FAT16.h>
#include <fat_config.h>
#include <partition.h>
#include <partition_config.h>
#include <sd-reader_config.h>
#include <sd_raw.h>
#include <sd_raw_config.h>

FAT TestFile;      //This will be the file we manipulate in the sketch
char buffer[512];  //Data will be temporarily stored to this buffer before being written to the file
int read_size=0;   //Used as an indicator for how many characters are read from the file
int count=0;       //Miscellaneous variable

void setup()
{
  Serial.begin(9600);  //Initiate serial communication at 9600 bps

  TestFile.initialize();  //Initialize the SD card and the FAT file system.
  Serial.println("Starting...");
  TestFile.create_file("Sample.txt");  //Create a file on the SD card named "Read_File_Test.txt"
                                       //NOTE: This function will return a 0 value if it was unable to create the file.
  TestFile.open();  //Now that the file has been created, open it so we can write to it.
}

void loop()
{
  TestFile.write("This is test data.");  //using the write function will always write to the beginning of the file. 
                                         // Here we add some text to the file.
  TestFile.close();  //We are done writing to the file for now. Close it for later use.

  while(1){
    TestFile.open();  //Open the file. When the file is opened we will be looking at the beginning of the file.
    read_size=TestFile.read(buffer); //Read the contents of the file. This will only read the amount of data specified
                                    // by the size of 'buffer.'

    Serial.println(read_size, DEC);  //Print the number of characters read by the read function.
    for(int i=0; iSerial.print(buffer[i], BYTE);  //Print out the contents of the buffer.
    }
    Serial.println();

    sprintf(buffer, "%d", count++); //Now we'll use the buffer to write data back to the file. 
                                   // Here's we'll only add one value to buffer, the 'count' variable. 
    TestFile.write(buffer);         //Write the new buffer to the end of the file
    TestFile.close();               //Close the file for later use.

    delay(1000);  //Wait one second before repeating the loop.
  }
}

这样Arduino在运行的时候，会不断地向SD卡模块上的Sample.txt文件中写入相应的数据，随后我们同样可以通过读卡器读出该文件中记录的内容。

需要注意的是，由于用来操作SD卡和文件系统的代码相对较多，目前该模块只能运行在带有ATmega328P的Arduino上面。另外，目前市场上可选的SD卡种类繁多，可能不是每种SD卡都能够被很好的兼容，目前我测试过通过的SD卡有：

• SanDisk 2GB SD2 Card
• Apacer 60X 1GB SD Card

测试没有通过的SD卡有：

• SanDisk 16MB SD Card