Lecture 2.1 - Ethernet Client

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From the course by University of California, Irvine

Interfacing with the Arduino

1562 ratings

University of California, Irvine

Interfacing with the Arduino

1562 ratings

Course 3 of 6 in the Specialization An Introduction to Programming the Internet of Things (IOT)

Arduino senses the environment by receiving inputs from add-on devices such as sensors, and can control the world around it by adjusting lights, motors, and other actuators. In this class you will learn how and when to use the different types of sensors and how to connect them to the Arduino. Since the external world uses continuous or analog signals and the hardware is digital you will learn how these signals are converted back-and-forth and how this must be considered as you program your device. You'll also learn about the use of Arduino-specific shields and the shields software libraries to interface with the real world. Please note that this course does not include discussion forums.

From the lesson

Module 4

In this module we’ll examine Arduino shields and how they are used to extend the capabilities of an Arduino-based system. Shields are printed circuit boards that are stacked on top of the Arduino together with libraries that enable the new hardware to be used through an Arduino sketch. We’ll describe the benefits of shields and their basic construction as well as the use of libraries in interfacing with each shield. This module also describes how to connect your IoT device to the Internet using shields. We focus on an Ethernet shield in order to establish a wired network connection, and a WiFi shield to establish a wireless connection.

Lecture 2.1 - Ethernet Client4:21

Lecture 2.2 - Client Examples4:20

Lecture 2.3 - Ethernet Server5:31

Lecture 2.4 - Ethernet Shield Demo11:01

Meet the Instructors

Ian Harris
Professor
Department of Computer Science

[MUSIC]

So remember that, typically, the Internet is used in this client-server

relationship, not always, but that's what we're assuming here.

So client-server relationship, what this means is that the server sits there, and

waits for connections, right.

Like a web server, it sits there, and has some kind of service it's providing.

Like a web server, it provides a web page.

It provides web pages.

So it sits there on the network, listening and waiting for connections, for

people to request something.

Then a client does the requesting.

So a client connects to the server and request some service.

Like request a web page, please give me a web page or something like that.

So we're assuming this client server relationship.

Our Ethernet shield can act as a client or a server.

So right now we are going to talk about using the Ethernet shield as a client.

When you do that, first thing you do is you have to create a client object, okay.

So Ethernet Client is the name of this class.

You say EthernetClient client, and that creates a client object.

You need that if you wanna act as a client.

So you create the client object, then you need to connect to a server, right.

If you're a client,

you're gonna wanna connect to a server to get some service from.

So you can do that, we're showing two ways of doing it,

basically you're calling this function called client.connect.

Now client.connect, it takes two arguments.

The first argument, well actually we showed two calls right here.

The first call, its two arguments are IP address and a port.

So you gotta give the IP address and the port number as its two arguments and

then it knows what machine to talk to.

Or you can pass the two arguments of the domain name and the port.

And, remember, using Domain Name Service, DNS,

the domain name can automatically be translated into an IP address.

So either way is fine.

client.connect you can call it, give it an IP address and a port number and

it makes a connection with a server.

Now notice that line of code says result equals client.connect, result equals.

So what that means is that client.connect is gonna return either a zero or a one.

True or false.

It returns a one if a connection is successfully made with a server.

It returns a zero if it's not.

And so then in your code you can say if result then da da da, right.

So you can check to see if a connection was successfully made before you go on and

start communicating.

And client.stop that stops the connection.

It ends the connection.

So when you're done communicating, you just go client.stop and

it closes the connection.

So sending, receiving data.

Now once you've made your connection, your client has made a connection to

the server, you want to send data to the server and receive data from the server.

So they have functions for that.

client.print or client.println that sends data.

print just sends the data and println sends the data and

sends a carriage return at the end.

That's common for sort of visible type data.

If you're sending a line you

just wanna put the carriage return in there automatically sometimes.

So print, and println, client.print, client.println are used to send data.

Now, and println is the character term.

Data is a string, so if you wanna send strings you use print or println.

Or an array of bytes which is also a string.

Same thing.

Now if you just wanna send raw data, it's not a string at all,

then you call client.write and you just pass the value, whatever it is.

If you send a byte values a byte you can send the client.write it'll send a byte.

Now client.read is used to do the opposite.

If want to read data.

If you're trying to read data from the server.

It calls client.read.

No arguments and that just reads the next available byte.

The next byte that's coming from the server.

And it returns that.

So data equals client.read,

data is gonna end up equaling whatever byte was received from the server.

Also, you can call client.available.

Client.available lets you know if there is data waiting.

So if client.available returns one, that means there is data waiting so

you can call client.read.

If client.available returns to zero,

then there's no point in calling client.read because it will fail.

Thank you.

[MUSIC]

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