ef. Adding a flash memory (SD card) card to ESP8266-13 module
ESP8266 module is one of the cheapest ways to connect and control homebuilt electronics devices to IoT Wi-Fi networks. A powerful Tensilica’s L106 Diamond series 32-bit processor provides not only for fast communication, but it can also act as a device controller. L106 processor has no internal EEPROM to store inbuilt software or user programs and it needs an external serial EEPROM to operate. ESP8266 is therefore a two chip module, and its version is more or less defined by size of the EEPROM chip and a number of implemented external input/output pins and. ESP8266 modules also defer by internal crystal oscillator speed.
Variety of memory cards
MMC, SD and miniSD memory cards connect to ESP8266 in an SPI mode through four wires: HSPI_MISO-->Din, HSPI_MOSI<--Dout, HSPI_CLK-->SCK and ~HSPO_CS-->~CS. Locations of SPI pins on an ESP8266 module depend on the module version. The schematic on this webpage is for ESP8266-13 module. Arduino IDE provides a number of programming libraries that make memory card file access easy.
A flash memory card to ESP8266-13 module connection (click the picture to enlarge)