Tired of ejecting the SD card from 3d Printer for adding new gcode - this adapter makes it WiFi enabled, i.e. you can remotely upload the gcode from your computer to the SD card.

This module based on ESP8266 reads/writes to SD card, and also leaves the SD card interface open to reading from 3d printer.

It works well with the RAMBO board and Marlin firmware in my printer, but should work in any setup that uses a SD card. A Toshiba Flash Air SD card which is commercially available, will do this as well, in case you want to save the trouble of soldering and programming chips.

Details:
My printer uses "RepRap full graphic LCD controller" and supports printing from a SD card. I replaced the SD card with this module - which is a blank fullsize SD card adapter, ESP8266 and a microSD card. See the wiring diagram.

The ESP8266 runs a WebDAV server which is the protocol for accessing networked drives and supported by Windows and other operating systems. This server can be accessed from a Windows machine by mapping a network drive, or directly running a command: \esp_hostnameDavWWWRoot

This ESP8266 web drive appears like any other networked drive and the files/directories can be added/deleted to it. Any files (gCodes) uploaded to this web drive, can be read by the 3d printer. The only limitation of this networked SD card drive is that the read/writes are a bit slow and ESP8266 firmware avoids accessing the SD card when host (3d printer) is reading/writing to it.

The schematic and codebase is available here: https://github.com/ardyesp/ESPWebDAV

The stl file is the module cover, just to publish this project.

Update Oct/2019:
Added a PDF document which describes the card implementation and use written by @skrutch