SD Card Module Symbol
Definition: The SD Card Module symbol represents a microSD/SD card interface breakout module in electronic schematic diagrams, denoting a board-level device that adapts an SD or microSD flash storage card to a standard 4-wire SPI bus (MOSI, MISO, SCK, CS) with onboard 3.3 V logic-level translation, enabling FAT32 file-system storage from 5 V microcontroller systems.
Also known as: microSD module, SD card breakout, SPI SD module, FAT32 storage module, SD adapter board.
What the SD Card Module symbol means
The SD Card Module symbol marks the physical module that bridges a microcontroller's SPI interface to an SD or microSD storage card. The module contains a card slot, a 3.3 V LDO regulator, and level-shift circuitry so that 5 V logic (e.g. Arduino Uno) can communicate safely with 3.3 V SD card logic without damaging the card.
In a circuit diagram the module symbol shows at minimum three signal pins — MOSI, MISO, and SCK — plus one or more chip-select lines (CS), a VCC supply, and a GND reference. The SD Card Module is a passive adapter in the power sense; all storage logic is handled inside the SD card itself according to the SD Association Physical Layer Specification.
How to identify the SD Card Module symbol
The SD Card Module symbol is drawn as a labelled rectangular IC block with the module name or 'SD' inscribed. Input pins on the left side include VCC and GND (power) and MOSI (data from host), while output/bidirectional pins on the right include MISO (data to host). Clock (SCK or CLK) and chip-select (CS) appear as additional left-side inputs. Some representations include a small card-slot graphic.
Function in a circuit
The SD Card Module provides SPI-bus access to an SD or microSD flash memory card, allowing a microcontroller to read and write files using a FAT16 or FAT32 file system. The onboard voltage regulator steps 5 V down to 3.3 V for the card, and the level-shifter translates SPI logic levels bidirectionally so that 5 V and 3.3 V microcontrollers can both use the same module.
Standards: IEC vs ANSI
| IEC 60617 | No dedicated IEC 60617 symbol exists for an SD card module; it is represented under IEC 60617 as a general rectangular IC/module block with labelled pins. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 similarly represents module-level devices as labelled rectangular blocks. The SD Physical Layer Simplified Specification (SD Association) governs the SD card interface protocol itself. |
| Key difference | IEC and ANSI use the same generic module-block symbol. The SD card protocol is standardised by the SD Association (not IEC or ANSI), with SPI compatibility defined in Part 1 of the SD Physical Layer Specification. |
Terminals / pins
| Pin | Name |
|---|---|
| vcc | VCC |
| gnd | GND |
| mosi | MOSI |
Typical values
Supply voltage: 3.3 V–5 V (module input); internal card voltage: 3.3 V. SPI clock: up to 25 MHz (SD default speed) or up to 50 MHz (high-speed mode). Storage: 2 GB (SD), 2 GB–32 GB (SDHC FAT32), 64 GB+ (SDXC exFAT). Quiescent current: 0.2 mA–2 mA (idle); 100 mA peak during write.
Where the SD Card Module symbol is used
- Arduino and microcontroller data-logging projects recording sensor readings to CSV files on a FAT32-formatted microSD card
- Embedded weather stations logging temperature, humidity, and pressure data for later retrieval
- GPS track loggers storing NMEA sentence streams to an SD card for route playback
- Audio players and recorders reading WAV or MP3 files from SD card storage via SPI
- DIY oscilloscopes and logic analysers storing captured waveform data to SD for PC analysis
- Industrial data loggers in PLCs or custom embedded systems where onboard flash is insufficient
Example
In an Arduino Uno data-logger schematic, the SD Card Module is connected with MOSI to pin 11, MISO to pin 12, SCK to pin 13, and CS to pin 10; VCC is fed from the 5 V rail and GND to the system ground. The module's onboard level-shifter protects the 3.3 V SD card from the Uno's 5 V SPI lines.
Key facts
- The SD Card Module symbol represents a breakout board, not the SD card itself; the module adds 3.3 V regulation and SPI-level shifting to allow 5 V microcontrollers to interface with 3.3 V SD cards.
- The SPI interface uses four signal lines: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCK (Serial Clock), and CS (Chip Select) — the same bus that is used by many other peripherals such as displays and ADCs.
- FAT32 file system support requires a software library on the microcontroller (e.g. SD.h on Arduino or FatFs on STM32) — the SD Card Module hardware provides only the physical interface, not file-system logic.
- The SD Association Physical Layer Simplified Specification defines the SPI operating mode used by most microcontroller SD libraries, distinct from the native SD bus (4-bit SDIO) mode used by higher-performance hosts.
- MicroSD cards draw up to 100 mA during write operations; the onboard LDO regulator on the module must be rated accordingly, making adequate power supply decoupling essential.
- Card detection is handled by a mechanical switch inside the card slot that connects a CD (card detect) pin to GND when a card is inserted; some module symbols include this optional CD pin.
- The maximum SPI clock frequency for reliable SD card access is 25 MHz in default speed mode and 50 MHz in high-speed mode, though most Arduino libraries default to lower frequencies for compatibility.
Frequently asked questions
What does the SD card module symbol mean in a schematic?
The SD card module symbol represents a breakout board that connects an SD or microSD flash card to a microcontroller via SPI. It includes onboard 3.3 V regulation and level-shifting so that 5 V systems can use 3.3 V SD cards safely.
What pins does the SD card module symbol show?
The SD card module symbol shows VCC and GND (power), MOSI (data to card), MISO (data from card), SCK/CLK (clock), and CS (chip select). Some symbols also include a CD (card detect) pin. The MOSI pin appears at x=0, y=22 in the reference symbol.
What SPI pins are needed to connect an SD card module to an Arduino?
Connect MOSI to Arduino pin 11, MISO to pin 12, SCK to pin 13, and CS to any digital output pin (commonly pin 10). Supply VCC from the 5 V rail and connect GND to the common ground.
What file system does an SD card module use?
SD card modules communicate with FAT16 (up to 2 GB SD cards) or FAT32 (2 GB–32 GB SDHC cards) file systems. exFAT is used on 64 GB+ SDXC cards. File-system handling is done by a software library on the microcontroller, not by the module hardware.
What is the difference between the IEC and ANSI symbol for an SD card module?
Neither IEC 60617 nor ANSI Y32.2 / IEEE 315 defines a dedicated symbol for an SD card module. Both standards use the same generic labelled rectangular block to represent module-level devices, so the symbol is identical under both conventions.
What voltage does the SD card module operate at?
The module input accepts 3.3 V to 5 V. Internally, the onboard LDO regulator supplies 3.3 V to the SD card. The bidirectional level-shifter translates SPI logic levels between the host microcontroller voltage and the 3.3 V card voltage.
What is the maximum SPI clock speed for an SD card module?
SD cards support SPI clock speeds up to 25 MHz in default speed mode and 50 MHz in high-speed mode. Most Arduino-based libraries initialise at a lower clock (400 kHz for card initialisation, then up to 4–20 MHz for data transfer) for broad compatibility.
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