Overview

MicroSD memory cards (originally known as TransFlash) provide a compact and inexpensive way to add gigabytes of non-volatile storage to a project. All SD cards support communication over the SPI (Serial Peripheral Interface) bus, making it straightforward to interface one of these cards with an SPI-capable microcontroller.

This carrier board makes it easy to connect to a microSD card by breaking out all of the contacts from a microSD card socket into two rows of 0.1″-spaced pins. The board measures only 0.8″ × 0.7″, and a set of breakaway 0.1″ male header strips (one 1×7 and one 1×4) is included, which can be soldered in to use the board with breadboards, perfboards, or 0.1″ female connectors. (The headers might ship as a single 1×11 piece that can be broken in two).

Breakout Board for microSD Card with included header pins.

Breakout Board for microSD Card plugged into a breadboard with microSD card (not included) inserted.

We also carry a larger microSD card breakout board with a 3.3V regulator and level shifters that can be directly integrated into 5 V systems; it only breaks breaks out the more commonly used SPI bus mode interface pins, and it includes two mounting holes. The pictures below show the two versions side-by-side.

Breakout Board for microSD Card.

Breakout Board for microSD Card with 3.3V Regulator and Level Shifters.

Using the breakout board

Since many microcontrollers have built-in SPI interfaces, most hobbyist projects communicate with Secure Digital cards in SPI bus mode. (The alternative SD bus mode is proprietary, and a license from the SD Association is required for access to the full specifications.) Where applicable, the pins on this board are labeled according to their functions in SPI mode.

All of the microSD card’s power pins and all of the signal pins necessary to interface with the card through SPI are available along the right side of the board. The left side of the board exposes duplicate power pins, along with two additional signal lines (DAT1 and DAT2) that are not needed for SPI communication but are used in 4-bit SD bus mode. The DAT1 pin also serves as an interrupt pin (IRQ) in SDIO devices. (Note that if you are using this module in a breadboard, you might want to solder header pins into both sides of the board for added stability even if you only plan to use the SPI pins.)

The following tables describe the function of each pin on the breakout board in SPI and SD mode:

Pin Description
GND
(VSS)
Power and logic ground
VDD Supply voltage (2.7 V to 3.6 V for standard microSD cards)
CD Card detect. When a card is inserted, this pin is floating; when no card is inserted, it is shorted to ground. A pull-up resistor can be used to pull the line high when a card is present.
SPI mode SD mode
Pin Description Pin Description
DI Data in (MOSI) CMD Command/response
DO Data out (MISO) DAT0 Data (bit 0)
SCLK Clock CLK Clock
CS Chip select (active low) DAT3 Data (bit 3)

IRQ
Reserved
Interrupt (active low; SDIO devices only)
DAT1
IRQ
Data (bit 1)
Interrupt (active low; SDIO devices only)
Reserved DAT2 Data (bit 2)

Warning: Standard microSD cards use 3.3 V logic level signals, so level shifters or voltage dividers are required when connecting one to a 5 V system.

Communicating with a microSD card

The SD Association publishes a set of simplified specifications for SD cards containing information on interfacing with them. However, there are a number of ways to get started without understanding the specifications or writing your own code from scratch, since many microcontroller development platforms provide libraries for communicating with SD cards. For example:

Schematic

Breakout Board for microSD Card schematic diagram.

This schematic is also available as a downloadable pdf (140k pdf).


Specifications

Dimensions

Size: 0.8″ × 0.7″ × 0.12″1
Weight: 1.3 g2

Notes:

1
Without a microSD card or the included optional header pins. When inserted, a microSD card will extend approximately 35 mil (0.85 mm) past the edge of the board.
2
Without a microSD card or the included optional header pins.

Resources

File downloads

Breakout Board for microSD Card schematic diagram (140k pdf)
Printable schematic for the Breakout Board for microSD Card.

(PL-2597)

SKU PL-2597
Brand Pololu

Be The First To Review This Product!

Help other Little Bird Company Pty Ltd users shop smarter by writing reviews for products you have purchased.

Write a product review


Others Also Bought



More From This Category