Example project · Builds & projects
microSD write & read-back
A real 64 MB SD card in SPI mode: the Uno runs the honest init handshake (CMD0, CMD8, ACMD41), writes a message into a raw block through the hardware SPI port, reads it back with CMD17 and prints it on the serial monitor — watch the activity LED blink on the breakout. The card ships FAT16-formatted, so the Code tab’s SdFat sketch (compile & upload) can write real files to it too.
What's on the bench
- Arduino Uno R3
- Battery
- microSD card
How it's wired
- Battery · pos→Arduino Uno R3 · 5v
- Battery · neg→Arduino Uno R3 · gnd
- Arduino Uno R3 · 3v3→microSD card · vcc
- Arduino Uno R3 · gnd2→microSD card · gnd
- Arduino Uno R3 · d13→microSD card · sck
- Arduino Uno R3 · d11→microSD card · mosi
- Arduino Uno R3 · d12→microSD card · miso
- Arduino Uno R3 · d10→microSD card · cs
The code
This Arduino C++ sketch lives in the Code tab; sign in and press Compile & upload to build real firmware for the emulated board.
// The same card through the MIT-licensed SdFat library (the card comes // FAT16-formatted, so sd.begin just works). CS on pin 10; SdFat drives // the hardware SPI port (11/12/13) itself. #include <SdFat.h> SdFat sd; void setup() { Serial.begin(9600); if (!sd.begin(10)) { Serial.println("card init failed"); return; } Serial.println("SD init OK"); File f = sd.open("log.txt", FILE_WRITE); f.println("HELLO FROM SD :)"); f.close(); f = sd.open("log.txt"); Serial.print("log.txt: "); while (f.available()) Serial.write(f.read()); f.close(); } void loop() {}
