{"id":5327,"date":"2026-08-30T15:20:53","date_gmt":"2026-08-30T06:20:53","guid":{"rendered":"https:\/\/donguri3.net\/server-tech\/rp2350-sd-card-read-write-adapter-reuse-2\/"},"modified":"2026-08-30T15:20:55","modified_gmt":"2026-08-30T06:20:55","slug":"rp2350-sd-card-read-write-adapter-reuse","status":"publish","type":"post","link":"https:\/\/donguri3.net\/en\/diy-repair\/electronics-microcontroller\/rp2350-sd-card-read-write-adapter-reuse\/","title":{"rendered":"\u3010RP2350\u3011No SD Card Module Required! Read and Write Data by Reusing a Spare Conversion Adapter"},"content":{"rendered":"

Following our setup of the RP2350 board last time, today we’ll take on the challenge of reading and writing data to an SD card.<\/p>\n

\"RP2350<\/a><\/p>\n

While an SD card is essential for recording sensor data and saving configuration files, you typically purchase a dedicated connection module to use one. However, if you have any leftover “SD card conversion adapters” that come with MicroSD card purchases, you can modify one and use it as a slot.<\/p>\n

In this post, I’ve compiled the steps for reading and writing data with the RP2350 using a spare adapter at hand, without buying an extra dedicated module. I’ll also share my personal soldering tips for wiring heat-sensitive plastic adapters without ruining them.<\/p>\n

First, Verify Operation with a Commercial Module<\/h2>\n

If you jump straight into testing a homemade slot and it doesn’t work, it’s impossible to isolate whether the issue lies in the wiring or the program. First, I ran a communication test with the RP2350 using a commercially available SD card module I had on hand.<\/p>\n

https:\/\/www.amazon.co.jp\/Youmile-%E3%82%AB%E3%83%BC%E3%83%89%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%BC%E3%83%AB%E3%83%9E%E3%82%A4%E3%82%AF%E3%83%AD-%E3%82%AB%E3%83%BC%E3%83%89%E3%82%A2%E3%83%80%E3%83%97%E3%82%BF%E3%83%AA%E3%83%BC%E3%83%AB%E3%83%BC%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%BC%E3%83%AB-%E3%82%A4%E3%82%B3%E3%83%B3%E3%83%86%E3%83%95%E3%82%A7%E3%82%A4%E3%82%B3%E3%83%AC%E3%83%99%E3%83%AB%E5%A4%89%E6%8F%9B%E3%83%81%E3%83%83%E3%83%97%E4%BB%98%E3%81%8D-Arduino\/dp\/B0C6KB34GZ?__mk_ja_JP=%E3%82%AB%E3%82%BF%E3%82%AB%E3%83%8A&crid=2PW8Y13T3GS8D&dib=eyJ2IjoiMSJ9.m8SM4sR8QfB275k0RUy78Vq3b9wL593ElB33-QqBB33NElkBqk4kqXGxQFqLabLiiI_e5HxbO6mAMQqKC5yKr9NMnHv7blUipth8DAQS90DAjnlCNTAufu1EdIrWASXQLLVGXshww9bz6-i6Ey1ujxhhyUoWNXS9sxCxPN9GOqndOkjdOFhF4ZYgA_8eniaDJS-pBOr6G38iW6_G-yAMj2wxSUYpayb6jqgk3toBt4olqjsjmKUN7EQ95UUC4s5Q82zEVfw3iLlJT1QXBfA4G6E_q9Kk3RyrkLRcA60Tquc.p3v0QlKBzLtNpjcpIgAAZ4u8H1jDLXZbk8usMnakLoM&dib_tag=se&keywords=10%E5%80%8BSD%E3%82%AB%E3%83%BC%E3%83%89%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%AB%E3%83%9E%E3%82%A4%E3%82%AF%E3%83%ADSD+SDHC+TF%E3%82%AB%E3%83%BC%E3%83%89%E3%82%A2%E3%83%80%E3%83%97%E3%82%BF%E3%83%AA%E3%83%BC%E3%83%80%E3%83%BC%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%AB+SPI%E3%82%A4%E3%82%B3%E3%83%B3%E3%83%86%E3%83%95%E3%82%A7%E3%82%A4%E3%82%B3%E3%83%AC%E3%83%99%E3%83%AB%E5%A4%89%E6%8F%9B%E3%83%81%E3%83%83%E3%83%97%E4%BB%98%E3%81%8D%E3%83%94%E3%83%B3%E3%83%83%E3%83%80%E3%83%BC%E4%BB%98%E3%81%8Dfor+Arduino%E7%94%A8&qid=1769690438&sprefix=10%E5%80%8Bsd%E3%82%AB%E3%83%BC%E3%83%89%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%AB%E3%83%9E%E3%82%A4%E3%82%AF%E3%83%ADsd+sdhc+tf%E3%82%AB%E3%83%BC%E3%83%89%E3%82%A2%E3%83%80%E3%83%97%E3%82%BF%E3%83%AA%E3%83%BC%E3%83%80%E3%83%BC%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%AB+spi%E3%82%A4%E3%82%B3%E3%83%B3%E3%83%86%E3%83%95%E3%82%A7%E3%82%A4%E3%82%B3%E3%83%AC%E3%83%99%E3%83%AB%E5%A4%89%E6%8F%9B%E3%83%81%E3%83%83%E3%83%97%E4%BB%98%E3%81%8D%E3%83%94%E3%83%B3%E3%83%83%E3%83%80%E3%83%BC%E4%BB%98%E3%81%8Dfor+arduino%E7%94%A8%2Caps%2C191&sr=8-1&linkCode=sl1&tag=nando09e-22&linkId=769d5a20b8fd598d01cdd55395ff20c7&language=ja_JP&ref_=as_li_ss_tl<\/a><\/p>\n

While this is a reassuring design featuring a 3.3V\/5V level shifting chip, the RP2350 (3.3V) can operate even with a direct connection.<\/p>\n

Introducing the “SdFat” Library<\/h2>\n

Before running tests, install the library for handling SD cards in the Arduino IDE. This time, we will use SdFat<\/span>, which is highly functional and works great with the RP2350.<\/p>\n

    \n
  1. Open the Arduino IDE menu and go to “Tools” -> “Manage Libraries…”.<\/li>\n
  2. Search for SdFat<\/span> and install it.<\/li>\n<\/ol>\n

    I performed a read\/write test using this library and confirmed that it works properly. Great, now the microcontroller and software setup are complete.<\/p>\n

    Attempting Direct Soldering to the Conversion Adapter<\/h2>\n

    Now, this is where the real work begins. The terminals of the conversion adapter are gold-plated, making it easy for solder to adhere… or so you’d think, but the base is made of heat-sensitive plastic. If you hesitate, heat will conduct and deform the inside, making it impossible to insert an SD card.<\/p>\n

    While the conventional wisdom has been to “solder with a dummy SD card inserted to prevent deformation,” I solved this using the power of tools and chemistry.<\/p>\n

    Nando Kobo Style: The Secret to Soldering Without Melting
    The key to success is “minimizing the time heat is conducted to an absolute minimum.” To achieve this, I used the following tool.<\/p>\n

    https:\/\/amzn.to\/3LJns5I<\/a><\/p>\n

    Using a toothpick or similar tool, dab just a small amount of this onto the tips of the adapter’s terminals.<\/p>\n

    https:\/\/amzn.to\/3LJns5I<\/a><\/p>\n

    Since there are no wires in the way, your hands won’t slip, allowing you to hit the exact target spot in one go.<\/p>\n

    [Procedure]<\/b><\/h3>\n
      \n
    1. Apply paste to the tips of the terminals.
      \n      \"Applying<\/a><\/li>\n
    2. Pre-tin the soldering iron tip with a little solder.<\/li>\n
    3. Briefly touch the iron to the pasted area. The required time is 0.5 seconds!<\/b><\/li>\n
    4. Thanks to the effect of the paste, the solder flows smoothly onto the terminal instantly.<\/li>\n<\/ol>\n

      With this method, the job finishes before heat can conduct to the plastic part (the base), preventing deformation even without inserting a dummy card. “Soldering is about speed, not temperature.” This was the moment I truly realized that.<\/p>\n

      \"Soldering\"<\/a><\/p>\n

      Wiring and Program<\/h2>\n

      Connect the completed “DIY SD slot” to the RP2350.<\/p>\n

      [Wiring Diagram] (*Pin assignment with the terminal side facing you and the corner notch of the adapter in the upper left)<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
      Adapter Terminal (from left)<\/strong><\/td>\nSignal Name (SPI)<\/strong><\/td>\nRP2040-Zero<\/strong><\/td>\nRole<\/strong><\/td>\n<\/tr>\n<\/thead>\n
      Pin 9 (Far Left)<\/b><\/span><\/td>\nDAT2<\/span><\/td>\n(Not Connected)<\/b><\/span><\/td>\nNot used in SPI<\/span><\/td>\n<\/tr>\n
      Pin 1 (2nd)<\/b><\/span><\/td>\nCS<\/b> \/ DAT3<\/span><\/td>\nGP 5<\/b><\/span><\/td>\nChip Select<\/b> (Selecting communication partner)<\/span><\/td>\n<\/tr>\n
      Pin 2 (3rd)<\/b><\/span><\/td>\nMOSI<\/b> \/ CMD<\/span><\/td>\nGP 7<\/b><\/span><\/td>\nData Transmit<\/b> (Microcontroller -> SD)<\/span><\/td>\n<\/tr>\n
      Pin 3 (4th)<\/b><\/span><\/td>\nVSS1 (GND)<\/span><\/td>\nGND<\/b><\/span><\/td>\nGround *1<\/span><\/td>\n<\/tr>\n
      Pin 4 (5th)<\/b><\/span><\/td>\nVDD<\/span><\/td>\n3V3<\/b><\/span><\/td>\nPower Supply (3.3V)<\/span><\/td>\n<\/tr>\n
      Pin 5 (6th)<\/b><\/span><\/td>\nSCK<\/b> \/ CLK<\/span><\/td>\nGP 6<\/b><\/span><\/td>\nClock<\/b> (Communication timing)<\/span><\/td>\n<\/tr>\n
      Pin 6 (7th)<\/b><\/span><\/td>\nVSS2 (GND)<\/span><\/td>\nGND<\/b><\/span><\/td>\nGround *1<\/span><\/td>\n<\/tr>\n
      Pin 7 (8th)<\/b><\/span><\/td>\nMISO<\/b> \/ DAT0<\/span><\/td>\nGP 4<\/b><\/span><\/td>\nData Receive<\/b> (SD -> Microcontroller)<\/span><\/td>\n<\/tr>\n
      Pin 8 (Far Right)<\/b><\/span><\/td>\nDAT1<\/span><\/td>\n(Not Connected)<\/b><\/span><\/td>\nNot used in SPI<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

      \"Connection\"<\/a><\/p>\n

      Test Program<\/h3>\n

      We use the same code verified in Step 1. *Note: When using the SdFat library, use the class name SdFile instead of File.<\/p>\n

      #include &lt;SPI.h&gt;
      \n#include &quot;SdFat.h&quot;<\/p>\n

      \/\/ — Pin configuration (RP2350 \/ Pico 2) —
      \n\/\/ Uses the same pin layout as the RP2040
      \nconst int PIN_MISO = 4;
      \nconst int PIN_CS = 5;
      \nconst int PIN_SCK = 6;
      \nconst int PIN_MOSI = 7;<\/p>\n

      \/\/ SdFat configuration
      \nSdFat sd;
      \nSdFile myFile;<\/p>\n

      void setup() {
      \nSerial.begin(115200);<\/p>\n

      \/\/ Wait for serial connection
      \nwhile (!Serial) { yield(); }
      \ndelay(1000);<\/p>\n

      Serial.println(&quot;
      \n— RP2350 (Pico 2) SPI SD Card Test —&quot;);<\/p>\n

      \/\/ Display chip information (useful for blog screenshots)
      \nSerial.print(&quot;Board Target: &quot;);
      \n#if defined(ARDUINO_ARCH_RP2040)
      \nSerial.println(&quot;RP2040 \/ RP2350 Architecture&quot;);
      \n#else
      \nSerial.println(&quot;Unknown Architecture&quot;);
      \n#endif<\/p>\n

      \/\/ 1. SPI pin assignment (This function is also valid on the RP2350)
      \nSPI.setRX(PIN_MISO);
      \nSPI.setTX(PIN_MOSI);
      \nSPI.setSCK(PIN_SCK);<\/p>\n

      Serial.println(&quot;Initializing SD card…&quot;);<\/p>\n

      \/\/ 2. SD card initialization
      \n\/\/ The RP2350 is fast, but let’s test connection at a stable 16MHz first
      \nif (!sd.begin(PIN_CS, SD_SCK_MHZ(16))) {
      \nSerial.println(&quot;Error: SD card initialization failed.&quot;);
      \nSerial.println(&quot;- Check wiring?&quot;);
      \nSerial.println(&quot;- Check format (FAT32)?&quot;);
      \nsd.initErrorHalt(&amp;Serial);
      \nreturn;
      \n}
      \nSerial.println(&quot;Success: SD card initialized!&quot;);<\/p>\n

      \/\/ — Write test —
      \nSerial.print(&quot;Writing test.txt… &quot;);<\/p>\n

      if (!myFile.open(&quot;test_rp2350.txt&quot;, O_RDWR | O_CREAT | O_APPEND)) {
      \nSerial.println(&quot;Error: Failed to open file for writing.&quot;);
      \nreturn;
      \n}<\/p>\n

      \/\/ Record that the write is coming from the RP2350
      \nmyFile.println(&quot;Hello from RP2350 (Pico 2)! SPI write test successful.&quot;);
      \nmyFile.close();
      \nSerial.println(&quot;Done.&quot;);<\/p>\n

      \/\/ — Read test —
      \nSerial.println(&quot;Reading test.txt content:&quot;);
      \nSerial.println(&quot;————————-&quot;);<\/p>\n

      if (!myFile.open(&quot;test_rp2350.txt&quot;, O_READ)) {
      \nSerial.println(&quot;Error: Failed to open file for reading.&quot;);
      \nreturn;
      \n}<\/p>\n

      while (myFile.available()) {
      \nSerial.write(myFile.read());
      \n}
      \nmyFile.close();<\/p>\n

      Serial.println(&quot;
      \n————————-&quot;);
      \nSerial.println(&quot;Test Complete.&quot;);
      \n}<\/p>\n

      void loop() {
      \n\/\/ Do nothing
      \n}<\/p>\n

      Investing in Tools Leads to DIY Success<\/h2>\n

      Buying a cheap SD module for a few hundred yen is also a valid approach, but utilizing a conversion adapter you have on hand gives you the advantage of freely deciding the layout and orientation of the slot. Above all, I gained valuable experience knowing that “with the right flux, even difficult soldering jobs can be finished in an instant.”<\/p>\n

      This establishes an environment for reading and writing large volumes of data. Next time, I’ll try high-speed reading and writing using PIO SDIO with this SD card adapter.<\/p>\n","protected":false},"excerpt":{"rendered":"

      Following our setup of the RP2350 board last time, today we’ll take on the challenge of reading and writ […]<\/p>\n","protected":false},"author":4,"featured_media":2635,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_locale":"en_US","_original_post":"https:\/\/donguri3.net\/?p=2620","footnotes":""},"categories":[1163],"tags":[9,52,262,1053,1059,325,274,278,270],"class_list":["post-5327","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-electronics-microcontroller","tag-diy","tag-https","tag-rp2040-zero","tag-rp2350","tag-sd","tag-325","tag-274","tag-278","tag-270","en-US"],"_links":{"self":[{"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/posts\/5327","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/comments?post=5327"}],"version-history":[{"count":1,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/posts\/5327\/revisions"}],"predecessor-version":[{"id":5331,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/posts\/5327\/revisions\/5331"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/media\/2635"}],"wp:attachment":[{"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/media?parent=5327"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/categories?post=5327"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/donguri3.net\/wp-json\/wp\/v2\/tags?post=5327"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}