Uno R4 · SPI SD readback

The pinned MIT SdFat library creates p5.txt on the emulated card, writes breadboard-p5 and reads it back in Serial. D10 selects the card; D11/D12/D13 carry SPI. The card uses the board’s real 3.3 V rail. Recompiling requires SdFat 2.3.0.

What's on the bench

• Arduino Uno R4
• Battery
• microSD card

How it's wired

• Battery · pos→Arduino Uno R4 · 5v
• Battery · neg→Arduino Uno R4 · gnd
• Arduino Uno R4 · gnd2→microSD card · gnd
• Arduino Uno R4 · 3v3→microSD card · vcc
• Arduino Uno R4 · d10→microSD card · cs
• Arduino Uno R4 · d13→microSD card · sck
• Arduino Uno R4 · d11→microSD card · mosi
• Arduino Uno R4 · d12→microSD card · miso

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.

// Breadboard UNO R4 P5 SPI0 SD-card acceptance fixture.

#include <SdFat.h>

static SdFat sd;

void setup() {
  Serial.begin(115200);
  if (!sd.begin(10, SD_SCK_MHZ(8))) {
    Serial.println("sd begin failed");
    return;
  }

  FsFile file = sd.open("p5.txt", O_RDWR | O_CREAT | O_TRUNC);
  if (!file) {
    Serial.println("sd open failed");
    return;
  }
  file.print("breadboard-p5");
  file.sync();
  file.rewind();

  Serial.print("sd");
  while (file.available()) {
    Serial.write(file.read());
  }
  Serial.println();
  file.close();
}

void loop() {}

Firmware licence

Related projects

ESP32-S31 servo sweepESP32-S31 rotary encoderESP32-S31 four fading LEDsESP32-S31 rainbow ring