Define Global Variables

Now we need to define some global variables that the code will use to define things such as digital outputs and string variables to store messages in.

const int relay1 = 7; // relay 1 is on digital pin 7
const int relay2 = 8; // relay 2 is on digital pin 8

String cmd =""; // string variable to store messages in

We need to be able to control each relay with a digital I/O pin from the device thus we define a variable that is of the constant integer type and set it equal to the I/O pin that is going to be used to send the signal to the circuit that will energize the relay coil. In this case I am going to use D7 for relay 1 and D8 for relay 2.

A constant integer means that the variable can not be redefined later in the code.

We also need a string variable to store the serial data in so that they can be proccessed.