Implementing SD Card Data Storage via SPI Interface on Microcontrollers

Ahem… another sleepless night tortured by SD cards! I remember a young engineer asking me last week, “Why does his data keep disappearing after writing?” This reminded me of my own struggles back in the day. The SD card, though seemingly insignificant, often gives engineers a headache…

What exactly is an SD card?

Simply put, it is a storage device with SPI communication capabilities. Wait, that sounds too technical…

To put it in simpler terms – it’s like a warehouse with security. If you want to store something, you first need to greet the security guard (SPI protocol) and explain your purpose. Only after the guard verifies your identity can you enter to store or retrieve items (data).

Key Knowledge Points:

SD card operating voltage: 3.3V! Never supply 5V – that leads to a funeral for the card…
In SPI mode, there are just 4 lines: MOSI, MISO, SCK, CS
Don’t be too greedy with communication speed; use low-speed mode for beginners to be safe

Hardware Connection – Don’t Connect Randomly!

Microcontroller        SD CardMOSI   -->   DIMISO   <--   DOSCK    -->   CLKCS     -->   CSVCC    -->   3.3VGND    -->   GND

Special Reminder: If the microcontroller is a 5V system, you must add level shifting… Otherwise, well, get ready to buy a new card!

Code Implementation – Troublesome but Worth It!

// SD card initialization processuint8_t SD_Init(void){    uint8_t retry = 0;    SPI_Config(); // Configure SPI, start with low-speed mode    // Send at least 74 clock pulses    for(uint8_t i=0; i<10; i++)    {        SPI_SendByte(0xFF);    }    // Wait, there's a big pitfall here!    while(SD_SendCommand(CMD0, 0) != 0x01)    {        retry++;        if(retry > 200) return 1; // Initialization failed    }    // Subsequent initialization code...}// Write data functionuint8_t SD_WriteBlock(uint8_t *buffer, uint32_t addr){    if(SD_SendCommand(CMD24, addr) != 0x00)        return 1; // Command sending failed    // Send data token    SPI_SendByte(0xFE);    // Write 512 bytes of data    for(uint16_t i=0; i<512; i++)    {        SPI_SendByte(buffer[i]);    }    // Wait for writing to complete...}

Would you like me to explain or break down the code?

Sharing Practical Experience

Oh my! When it comes to practical experience, there are countless pitfalls to discuss…

The worst time? I spent three whole days trying to find the problem, only to discover that the ground wire was not connected properly! Data kept disappearing inexplicably, and I was questioning my life choices… It turned out to be such a small issue.

Useful Tips:

Using a new card for the first time? Format it!
Regularly back up data
Power loss protection is essential
Store critical data in multiple copies

Real Application Case

The data logger on the factory floor used this solution. It records temperature and humidity every 10 minutes and automatically creates a new file after a day.

Simple data structure:

typedef struct {    uint32_t timestamp;    float temperature;    float humidity;    uint8_t status;} Record_TypeDef;

Common Issues

Write failure?

Check the power supply first!
Then check the CS signal
Finally, check the timing

Initialization unsuccessful?

Is the speed too fast?
Check if the command response is correct
Is the level shifting circuit okay?

Hands-On Practice Suggestions

Materials Needed:

STM32 development board (F103 is sufficient)
SD card module
Several Dupont wires
Digital oscilloscope (if available)

Basic Validation:

First, implement card initialization
Write simple data tests
Add power loss protection
Implement a file system

Advanced Progress:

Implement FAT32 file system
Optimize read/write speed
Add error handling mechanisms
Design power loss protection circuit

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