Now, we are going to build our first interesting application using the system we just assembled. We are going to build an Arduino sketch to control the relay from anywhere within your local network. For example, if your computer is connected via Wi-Fi to your router and the Ethernet shield is connected to the same router, you will be able to control the relay via your computer. The advantage of this approach in this section is that even if your Internet connection is down, you will still be able to control the relay.

The application starts by including the correct libraries:

#include <SPI.h>
#include <Ethernet.h>
#include <aREST.h>

We set up the MAC address of the board:

byte mac[] = { 0x90, 0xA2, 0xDA, 0x0E, 0xFE, 0x40 };

We also define a default IP address for the board that will be used if DHCP fails:

IPAddress ip(192,168,1,150);

We then create an instance of the aREST library, which will handle the request that comes to the board:

aREST rest ...