“Those little plastic µSD-to-SD card adapters, of which you may have a bunch lying around since they are often included with new µSD cards, make excellent µSD card sockets: There are many libraries (in C for the Arduino, for example) which support accessing SD cards from an embedded µC. These all rely on a well-known feature of these cards of supporting SPI: The only tricky bit is getting them into that mode. For this, the SPI clock has to be temporarily lowered to 100..400 KHz, and then a few magic pin toggles and byte sends will do the rest.”