This sketch receives a command from HCA and triggers one of it relays accordingly.

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

// Enter a MAC address and IP address for your controller below.
// change these to appropriate values
byte mac[] = {  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0x68 };
IPAddress ip(192, 168, 0, 68);
unsigned int Port_Remote = 5000;      // remote port for status check
IPAddress IP_Remote(192, 168, 0, 10);           // IP address for smarthome
unsigned int localPort = 5001;      // local port to listen on
// we don’t check on the sender’s port or addr for now
char cmdGDoper = ‘1’;     // a “1” means flip the garage door opener
char cmdResetPC = ‘2’;   // a “2” means turn the computer off for 60 sec to reboot it
char cmdBathBlowerOn = ‘3’;    // a “3” means turn the bath room blower on
char cmdBathBlowerOff = ‘4’;  // a “4” means turn the bath room blower off
char cmdStatusCheck = ‘9’;        // a “9” means reply with good status
char cmdIn = ‘0’;        // used to obtain and compare buffer character
int garageDoorOperPin = 9;        // digital pin to control garage door opener
int resetPCPin = 8;                // digital pin to control pc relay
int bathBlowerPin = 7;                // digital pin to control blower
// can not use dig pins 2, 4, 10, 11, 12, 13
// An EthernetUDP instance to let us receive packets over UDP
EthernetUDP Udp;
char packetBuffer[UDP_TX_PACKET_MAX_SIZE]; //buffer to hold incoming packet

void setup() {
digitalWrite(garageDoorOperPin, HIGH);  // high=off for this relay
digitalWrite(resetPCPin, HIGH);
digitalWrite(bathBlowerPin, LOW);    // low=off for this relay
pinMode(garageDoorOperPin, OUTPUT);
pinMode(resetPCPin, OUTPUT);
pinMode(bathBlowerPin, OUTPUT);
// start the Ethernet and UDP:
Ethernet.begin(mac, ip);
Udp.begin(localPort);
delay(10000);
//    Serial.begin(9600);
// Serial.println(“Starting”);

}

void loop() {
int packetSize = Udp.parsePacket();
if(packetSize)
{
// Serial.print(“Received packet of size “);
// Serial.println(packetSize);
// Serial.print(“From “);
// IPAddress remote = Udp.remoteIP();
// for (int i =0; i < 4; i++)
//    {
//    Serial.print(remote[i], DEC);
//    if (i < 3)
//        {
//        Serial.print(“.”);
//        }
//    }
//
//  Serial.print(“, port “);
//  Serial.println(Udp.remotePort());

// read the packet into packetBufffer
Udp.read(packetBuffer,1);
//    Serial.print(“Contents:”);
//        Serial.println(packetBuffer);
cmdIn = (packetBuffer[0]);
// press garage door opener
if (cmdIn == cmdGDoper)
{
//      Serial.println(“matched1!”);
digitalWrite(garageDoorOperPin, LOW);  // relay uses NO connections
delay (100);    // oper relay for 0.1 sec
digitalWrite(garageDoorOperPin, HIGH);
}
// trip smarthome pc relay for a minute
if (cmdIn == cmdResetPC)
{
//      Serial.println(“matched2!”);
digitalWrite(resetPCPin, LOW);        // relay uses NC connections
delay (60000);        // delay for 60 seconds
digitalWrite(resetPCPin, HIGH);
}
// turn bath blower on
if (cmdIn == cmdBathBlowerOn)
{
//      Serial.println(“matched3!”);
digitalWrite(bathBlowerPin, HIGH);        // relay uses NO connections
}
// turn bath blower off
if (cmdIn == cmdBathBlowerOff)
{
//      Serial.println(“matched4!”);
digitalWrite(bathBlowerPin, LOW);        // relay uses NO connections
}
// reply to status check
// respond to status check
if (cmdIn == cmdStatusCheck)
//  Serial.println(“matched9!”);
{
Udp.beginPacket(IP_Remote, Port_Remote);
Udp.write(“ard68ok=yes”);        // send packet good status
Udp.endPacket();
}  // end of status check

}  // end of incoming packet handler
}  // end of main loop