Wireless Communication with XBee Radios - Exploring Arduino: Tools and Techniques for Engineering Wizardry - page 251

Listing 11-6: Doorbell Receiver—doorbell/receiving_arduino
//Code running on an Arduino to receive doorbell value
const int RED =11; //Red LED on pin 11
const int GREEN =10; //Green LED on pin 10
const int SPEAKER =8; //Speaker on pin 8
char data; //Char to hold incoming serial data
int onLED = GREEN; //Initially on LED
int offLED = RED; //Initially off LED
int freq = 131; //Initial speaker frequency
unsigned long prev_time = 0; //Timer for toggling the LED and speaker
void setup()
{
Serial.begin(9600); //Start serial
}
void loop()
{
//Handle light and sound toggling
//If 100ms have passed
if (millis() >= prev_time + 100)
{
//Toggle the LED state
if (onLED == GREEN)
{
onLED = RED;
offLED = GREEN;
}
else
{
onLED = GREEN;
offLED = RED;
}
//Toggle the frequency
if (freq == 261){
freq = 131;
} else {
freq = 261;
}
//Set the current time in ms to the
//Previous time for the next trip through the loop
prev_time = millis();
}
//Check if serial data is available
if (Serial.available() > 0)
{