A microSD memory card is a fingertip-sized (15 x 11 mm) flash memory card. In microcontroller projects it stores photos, sound files and measurement logs (data logging). Some boards such as the ESP32-CAM have their own microSD slot; on the Arduino and the Raspberry Pi Pico the card connects over SPI through a MicroSD Card Module. For hobby projects 4–32 GB microSDHC cards fit best: the Arduino and ESP32 SD libraries read the card in FAT32 format. Cards of 64 GB and above usually come formatted as exFAT and must be formatted as FAT32 first. The speed class (Class 10, U1) sets the write speed but makes no difference in small projects. The card runs on 3.3 V and must not be connected straight to a 5 V pin. Cutting the circuit's power before inserting or removing the card keeps the files from getting corrupted. It is used in MP3 playback with the DFPlayer Mini, weather station logs and photo saving with the ESP32-CAM.