Ethernet Shield

Adds a wired RJ45 network connection to an Arduino using the W5100 controller, which handles the TCP/IP stack in hardware so your sketch does not have to. That makes it far more reliable than software networking on a small microcontroller. Use it to serve a web page from your project, log data to a server or accept remote commands. A microSD slot is included for storing web pages or log files. Both the network chip and the SD card share the SPI bus, so pins 10, 11, 12 and 13 are reserved. Hardware TCP/IP stack, no processing burden on the Arduino; Stable wired connection where WiFi is unreliable; microSD slot for web pages and data logging; Supports up to four simultaneous socket connections