Regular SD-Card Baord with Attiny If you don't have the custom board, you can still connect a regular SPI SD card module to an ATTiny for the same purpose. Connect the SPI SD Card module to the Attiny ...

The reason is that SD cards operate around 3v3, but Arduino Uno GPIO pins are excited to 5v. However, these modules are still relevant because some other dev boards operate their GPIO pins with 3v3, ...