Telnet Client

This example connects to a Telnet server using an Ethernet shield. Messages from the server are printed out via the serial port. Messages can be sent to the remote server serially as well. The Serial monitor works well for this purpose.

Step 1: What You Need?

1 x Arduino Board ( Arduino UNO used in this tutorial) 
1 x Arduino Ethernet Shield

Software Required

- A telnet server 

- Alternatively, Processing has a ChatServer example that works well for this purpose

Don't have components? Don't worry. Just click the component's name. 

Step 2: Build Your Circuit.

The Ethernet shield allows you to connect a WizNet Ethernet controller to the Arduino boards via the SPI bus. It uses pins 10, 11, 12, and 13 for the SPI connection to the WizNet. Later models of the Ethernet shield also have an SD Card on board. Digital pin 4 is used to control the slave select pin on the SD card.

The shield should be connected to a network with an ethernet cable. You will need to change the network settings in the program to correspond to your network.

In the above image, the Arduino or Genuino board would be stacked below the Ethernet shield.

Step 3: Upload The Code.

1. Select the Arduino board type: Select Tools >> Board >> Select your correct Arduino board used.

2. Find the port number by accessing device manager on Windows. See the section Port (COM&LPT) and look for an open port named "Arduino Uno (COMxx)". If you are using a different board, you will find a name accordingly. What matters is the xx in COMxx part. In my case, it's COM3. So my port number is 3.

Select the right port: Tools >> Port >> Select the port number.

3. You can find this code in the example of Arduino IDE.

Select File >> Examples >> Ethernet >>TelnetClient

Click press the "upload" button (see the button with right arrow mark).

/*
Telnet client This sketch connects to a a telnet server (http://www.google.com)
using an Arduino Wiznet Ethernet shield. You'll need a telnet server
to test this with.
Processing's ChatServer example (part of the network library) works well,
running on port 10002. It can be found as part of the examples
in the Processing application, available at
http://processing.org/ Circuit:
* Ethernet shield attached to pins 10, 11, 12, 13 created 14 Sep 2010
modified 9 Apr 2012
by Tom Igoe */ #include <SPI.h>
#include <Ethernet.h> // Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};
IPAddress ip(192, 168, 1, 177); // Enter the IP address of the server you're connecting to:
IPAddress server(1, 1, 1, 1); // Initialize the Ethernet client library
// with the IP address and port of the server
// that you want to connect to (port 23 is default for telnet;
// if you're using Processing's ChatServer, use port 10002):
EthernetClient client; void setup() {
// start the Ethernet connection:
Ethernet.begin(mac, ip);
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
} // give the Ethernet shield a second to initialize:
delay(1000);
Serial.println("connecting..."); // if you get a connection, report back via serial:
if (client.connect(server, 10002)) {
Serial.println("connected");
} else {
// if you didn't get a connection to the server:
Serial.println("connection failed");
}
} void loop() {
// if there are incoming bytes available
// from the server, read them and print them:
if (client.available()) {
char c = client.read();
Serial.print(c);
} // as long as there are bytes in the serial queue,
// read them and send them out the socket if it's open:
while (Serial.available() > 0) {
char inChar = Serial.read();
if (client.connected()) {
client.print(inChar);
}
} // if the server's disconnected, stop the client:
if (!client.connected()) {
Serial.println();
Serial.println("disconnecting.");
client.stop();
// do nothing:
while (true);
}
}

Download:

Arduino IDE

Sources:https://www.arduino.cc/en/Tutorial/TelnetClient    

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My Robot Education Sdn. Bhd. (Robotedu.my) was founded in 2015 as the first robotics education centre in Malaysia to provide Arduino-based robotics courses for youths. Our vision is to be able to provide robotics education to every youth in Malaysia.