Interfacing the MicroSD Card & USB-to-UART Serial Monitoring

The Orbit-Q docking station integrates a physical MicroSD card slot routed via the SPI peripheral interface and a CP2102 USB-to-UART bridge connected to the board's serial line. Combining these two systems allows you to perform onboard data logging and view real-time debug outputs directly on your computer's Serial Monitor.

1. Hardware Overview & Jumper Configurations

MicroSD Card Interface (SPI): * Protocol: SPI (Serial Peripheral Interface) * Chip Select (CS) Pin: PA4 (as defined in your code) * Hardware Control (JP-5 Header): The MicroSD slot communicates via the STM32F405's hardware SPI bus. Ensure that the JP-5 configuration header jumpers are securely placed to bridge the SPI lines (MOSI, MISO, SCK, and CS) between the M.2 module and the onboard card holder. * Power & Activity Indicators: Verify that the SL-10 LED indicator is lit, confirming that the MicroSD card socket is receiving its required power supply.

USB-to-UART Serial Bridge (CP2102): * Purpose: Translates UART serial data from the STM32F405 into USB signals for your PC. * Hardware Control (JP-3 Header): Configure the JP-3 header to route the MCU's hardware UART TX/RX lines to the CP2102 bridge chip. * Data LEDs: Look for SL-6 (TX data transmission) and SL-7 (RX data reception) indicators to flash when data is moving between the board and your computer.

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2. Software Requirements & Library Installation

To handle file systems on the SD card efficiently, this tutorial uses the optimized SdFat library rather than the standard Arduino SD library.

1. In the Arduino IDE, open the Library Manager (Sketch > Include Library > Manage Libraries... or press Ctrl+Shift+I).
2. Search for SdFat by Bill Greiman.
3. Locate the library and click Install (install any recommended dependencies if prompted).

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3. Arduino IDE Sketch (Write & Read Test)

Connect your USB cable to the USB-1 port (connected to the CP2102 chip), select the appropriate COM port in the Arduino IDE, set your board options to the STM32F405, and upload the following tested sketch:

#include <SPI.h>
#include <SdFat.h>

#define SD_CS_PIN PA4

SdFat sd;
File file;

void setup() {
  Serial.begin(115200);
  delay(3000);

  Serial.println("STM32F405 USB Serial OK");
  Serial.println("Initializing SD card...");

  pinMode(SD_CS_PIN, OUTPUT);
  digitalWrite(SD_CS_PIN, HIGH);

  SPI.begin();

  if (!sd.begin(SD_CS_PIN, SD_SCK_MHZ(1))) {
    Serial.println("❌ SD init failed");
    sd.initErrorHalt(&Serial);
  }

  Serial.println("✅ SD init OK");

  // ---------------- WRITE ----------------
  Serial.println("Writing to file...");

  file = sd.open("test.txt", FILE_WRITE);
  if (!file) {
    Serial.println("❌ File open for write failed");
    return;
  }

  file.println("Hello from STM32F405!");
  file.println("SD card write + read test");
  file.println("HP 64GB SDXC card");
  file.close();

  Serial.println("✅ Write complete");

  // ---------------- READ ----------------
  Serial.println("Reading file back:");

  file = sd.open("test.txt", FILE_READ);
  if (!file) {
    Serial.println("❌ File open for read failed");
    return;
  }

  while (file.available()) {
    Serial.write(file.read());
  }

  file.close();
  Serial.println("\n✅ Read complete");
}

void loop() {
  // nothing here
}

4. Viewing Data via the CP2102 Serial Monitor

• Open the Arduino IDE Serial Monitor (Ctrl + Shift + M).
• Set the baud rate dropdown to 115200 to match Serial.begin(115200) in the code.

• Press the physical RESET button on the Orbit-Q board to restart the MCU. You should see the initialization text, write confirmations, and the contents of test.txt printed directly on the screen.

• Troubleshooting

SD Initialization Failed or Serial Monitor is Blank

• Check JP-5 & JP-3:Make sure the JP-5 jumpers are set correctly for SPI communication and JP-3 is configured for the CP2102 UART bridge. If JP-3 is open, no text will reach your Serial Monitor.
• Verify COM Port: Ensure you have selected the correct COM port associated with the CP2102 USB-to-UART bridge (not the DFU or native USB-OTG port) under Tools > Port.
• SD Card Formatting: Ensure your MicroSD card is formatted to FAT16 or FAT32 (exFAT is typically not supported by standard microcontroller FAT libraries).
• Baud Rate Mismatch: If the Serial Monitor prints gibberish characters, verify that your monitor baud rate is precisely set to 115200.