You can now either copy the code inside a file called Monitor_Ethernet.ino, or just get the complete code from the folder for this project; you need to use the Arduino  IDE.

The following are the libraries included in the program:

#include <SPI.h> 
#include <Ethernet.h> 
#include <aREST.h> 
#include <avr/wdt.h> 

Include the library for the DHT11 sensor:

#include "DHT.h" 

We define the pins for the temperature and humidity sensor:

#define DHTPIN 7  
#define DHTTYPE DHT11 

We have the instance of the sensor:

DHT dht(DHTPIN, DHTTYPE); 

We register the MAC address for the device:

byte mac[] = { 0x90, 0xA2, 0xDA, 0x0E, 0xFE, 0x40 }; 
IPAddress ip(192,168,1,153); 
EthernetServer server(80); 

We now create an instance of the aREST API:

aREST rest = aREST(); 

We publish the variables that will be monitored:

int temp; 
int hum; 
int light; 

We now configure serial communication and start the instance of the sensor:

void setup(void) 
{   
  // Start Serial 
  Serial.begin(115200); 
  dht.begin(); 

We start the variables to publish:

  rest.variable("light",&light); 
  rest.variable("temp",&temp); 
  rest.variable("hum",&hum); 

It is very important to give the ID and the name of the device that we are using:

  rest.set_id("008"); 
  rest.set_name("Ethernet"); 

We begin the Ethernet connection:

if (Ethernet.begin(mac) == 0) { 
    Serial.println("Failed to configure Ethernet using DHCP"); 
    Ethernet.begin(mac, ip); 
  } 

We display the IP address on the serial monitor:

  server.begin(); 
  Serial.print("server is at "); 
  Serial.println(Ethernet.localIP()); 
  wdt_enable(WDTO_4S); 
} 

We read the temperature and humidity sensor:

void loop() {   
 
  temp = (float)dht.readTemperature(); 
  hum = (float)dht.readHumidity(); 

We measure the light level of the sensor:

  float sensor_reading = analogRead(A0); 
  light = (sensor_reading/1024*100); 

We listen for the incoming clients that will be connected:

  EthernetClient client = server.available(); 
  rest.handle(client); 
  wdt_reset(); 
} 

Now that we have finished the configurations, we open a web browser and type the IP address of your Arduino Ethernet shield: http://192.168.1.153. If everything goes perfectly it will display the following screen with the JSON response from the board:

The preceding screenshot shows the results of the JSON request.

In this section, we will explain the code for configuring the devices that we can control from a web page.

We installed the express package in the previous section; if you have any difficulty, just open a terminal and type the following:

npm install express

We define the node express and create the app:

var express = require('express'), 
var app = express(); 

We then define the port to listen:

var port = 3000; 

We define the instance of Jade application, using the view engine: 

app.set('view engine', 'jade'), 

We configure the public folder:

app.use(express.static(__dirname + '/public')); 

We now define the devices to monitor:

var rest = require("arest")(app); 
rest.addDevice('http','192.168.1.153'), 

We serve the application:

app.get('/', function(req, res){ 
res.render('interface'), 
}); 

We start the server and send the message when the device is connected:

app.listen(port); 
console.log("Listening on port " + port); 

Open your terminal in MS-DOS and execute app.js in your Node.js server

To test the application, open your web browser and type http://localhost:3000; if a screen like the following, congratulations appears, you just configured your server properly:

Here we have the screen where we see the execution of app.js in the Node.js server: