The Arduino WiFi Shield allows an Arduino board to connect to the internet using the 802.11 wireless specification (WiFi). It is based on the HDG204 Wireless LAN 802.11b/g System in-Package. An Atmega 32UC3 provides a network (IP) stack capable of both TCP and UDP. Use the WiFI library to write sketches which connect to the internet using the shield. The WiFI shield connects to an Arduino board using long wire-wrap headers which extend through the shield. This keeps the pin layout intact and allows another shield to be stacked on top. There is an onboard micro-SD card slotwhich can be used to store files for serving over the network. It is compatible with the Arduino Uno and Mega. The onboard microSD card reader is accessible through the SD Library. When working with this librarySS is on Pin 4. Arduino communicates with both the Wifi shield’s processor and SD card using the SPI bus (through the ICSP header). This is on digital pins 1112and 13 on the Uno and pins 5051and 52 on the Mega. On both boardspin 10 is used to select the HDG204 and pin 4 for the SD card. These pins cannot be used for general I/O. On the Megathe hardware SS pin53is not used to select either the HDG204 or the SD cardbut it must be kept as an output or the SPI interface won’t work. Digital pin 7 is used as a handshake pin between the WiFi shield and the Arduinoand should not be used. Note that because the HDG204 and SD card share the SPI busonly one can be active at a time. If you are using both peripherals in your programthis should be taken care of by the corresponding libraries. If you’re not using one of the peripherals in your programhoweveryou’ll need to explicitly deselect it. To do this with the SD cardset pin 4 as an output and write a high to it. For the HDG204set digital pin 10 as a high output.