SD/SDHC Card Interfacing with ATmega8 /32 (FAT32 implementation)


Posted on Feb 6, 2014

Here is my project on interfacing of SD Card (microSD). microSD cards are available very cheap nowadays, a great option for having a huge memory in any embedded system project. It is compatible with SPI bus, so the interfacing is easy. SD card adapters are also easily available in market, one can easily make a bread-board adapter by soldering few


SD/SDHC Card Interfacing with ATmega8 /32 (FAT32 implementation)
Click here to download the full size of the above Circuit.

pins on it. Following figures show the SD card pin-out & the bread-board adapter design by soldering 7-pins of a breakout header on the microSD adapter (Click on images for larger view). I had started this project with 1GB microSD card from SanDisk (later on tested with transcend cards also). The microcontroller is AVR ATmega8 or ATmega32 running at 8Mhz internal clock. MAX232 is used to interface the circuit with PC for monitoring the data. A 3. 3v supply is used for powering the mega8, microSD and max232 (though the specified supply for max232 is 5v, it works comfortably at 3. 3v). 7 pins of the microSD are used here, shown in the figure of pin-out. Schematic for ATmega8 is shown here (updated on 10 May 2010, SD series resistors are removed, as they were limiting the speed of SPI bus. 51k pullups are added on CMD/DAT lines. This gives better stability with different cards. Also, two 3. 6v zeners are added to protect SD in case when the ISP programmer voltage levels are of 5v. these diodes are not required if your programmer has settings for 3. 3v output) Following is the schematic for ATmega32, with RTC (added on 17 May 2010; CS pin correction, PB4 instead of PB1, done in Mar 2014). Here two supply voltages are used, 3. 3v for SD & 5v for remaining ICs. The aim of this project was to learn interfacing of SD card and to understand the data transfer in raw format as well as in FAT32 format. I started with raw data transfer,...




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