Hello readers, I hope you all are having fun in your lives. Welcome to the 2nd Chapter of Section-2 in the ESP32 Programming Series. In today's lesson, we'll go over another built-in feature of the esp32 module that helps it stand out from the competition: BLE or Bluetooth Low Energy.
In the previous tutorial, we discussed the Classic Bluetooth in ESP32, which is considered the predecessor of Bluetooth Low Energy(which we are going to discuss today). We will first look at, what is BLE? and why is it used?, and then will design some examples to utilize the ESP32 BLE in Arduino IDE.
There have been numerous adjustments and upgrades to Bluetooth's characteristics since its inception, where Bluetooth 4.0(also called BLE or Bluetooth Smart) is the most influential.
BLE or Bluetooth Smart is also known as Wibree. The Wibree protocol was designed by Nokia in 2006 and was later included in Bluetooth 4.0 as Bluetooth Low Energy in December 2009.
Bluetooth Low Energy is a slightly different protocol from Classic Bluetooth, which is used in phones, headphones, TVs etc. Rather than continuously streaming data, BLE "servers" can "notify" clients to send the data chunks on a regular basis(which makes it preferable over traditional Bluetooth). As a result, BLE is better suited to low-power IoT applications that don't require significant volumes of data.
Both the server and clients now utilize a "service UUID", to determine which server and client needs to be connected. There are various "characteristics" that can be found inside these services.
Bluetooth Low Energy was developed and promoted by the Bluetooth Special Interest Group (SIG) for use in healthcare, beacons, fitness, home entertainment etc. It does not work with standard Bluetooth and does not have any compatibility, although it can coexist with BR/EDR and LE.
The Bluetooth Special Interest Group (SIG) recognizes several industries for low-energy technology, including smart homes, health, sport, and fitness.
Difference b/w traditional Bluetooth and BLE
Bluetooth Technology was created with the intention of allowing data to be streamed indefinitely. That implies you can send and receive a large amount of data over a short distance with Bluetooth.
It's crucial to discuss power usage while discussing the differences between Bluetooth and Bluetooth Low Energy. Bluetooth Low Energy is intended to transfer data only when the client is available to receive the data from the server; otherwise, the BLE device will go into low energy or sleep mode. Thus, use significantly less power as compared to traditional Bluetooth, while retaining a similar communication range.
Bluetooth Low Energy uses the same 2.4 GHz radio frequencies as traditional Bluetooth, but a different FHSS (Frequency Hopping Spread Spectrum) technique.
Classic Bluetooth uses Scatter-net topology whereas BLE uses Star topology.
Although Bluetooth Low Energy differs from the previous Bluetooth Basic Rate/Enhanced Data Rate protocol, both can be supported by the same device: the Bluetooth 4.0 specification allows devices to implement any or both of the LE and BR/EDR systems.
Because both, Bluetooth Low Energy and traditional Bluetooth use the same 2.4 GHz radio frequencies, allowing dual-mode devices to use a single radio antenna.
How does BLE work?
BLE Client & Server
Any BLE device can operate as both a server and a client.
Server ESP32 will announce its presence to nearby clients so that clients can establish a connection with the BLE server for communication.
Broadcast mode and mesh networks both are also supported by BLE.
In broadcast mode, only the BLE server transmits data to all the connected clients.
In mesh mode, all the devices are connected to each other. Therefore, all devices can communicate with all other available devices.
GATT
GATT is an acronym for Generic Attributes.
It defines a data structure that is visible to all BLE devices linked to it. GATT defines how BLE devices can communicate with each other. Understanding this structure is crucial to understand the working of BLE.
The GATT protocol includes a set of commands that allow the client to learn more about the server.
Read through all of the descriptors for a specific characteristic.
Find out everything there is to know about a specific service.
Find qualities that match a UUID.
Find UUIDs for all major services.
Find a service using a UUID.
For a particular principal service, locate subsidiary services.
BLE Service
A service is nothing more than a collection of data, such as data from a temperature sensor.
A profile, which is made up of multiple services, is at the top of the structure. Typically, a BLE-supported device will have multiple services.
The SIG has preset services for a variety of data kinds, such as battery level, weight, blood pressure, heart rate, and so on.
Every service has at least a single feature and can also refer to different services.
BLE Characteristics
The characteristic attribute is always held by a particular service, and it is where the hierarchy's real data is stored.
The characteristic has two attributes:
Characteristic value.
The characteristic declaration contains the metadata.
It essentially consists of the operations that can be used like Indicate, read, write, notify, broadcast etc.
UUID or Universally Unique Identifier
In a Generic Attribute (GATT) profile, the UUID is a universally unique 128-bit or 16-byte integer that is used to identify profiles, services, and data kinds.
Note:
In the code description, we will provide a link where you can generate a new UUID.
BLE network topology
BLE uses Star and mesh topology for communication.
A Broadcast Type or a Connection Type communication between two BLE devices is possible. The 'broadcaster' BLE Device sends data to any 'observer' BLE Device in broadcasting. It's a data transfer that only goes one way.
A 'Connection' between the BLE Devices is required for two-way communication. A Central (Master) BLE Device continuously checks for advertising data packets sent by a Peripheral (Slave) BLE Device.
BLE Applications
BLE is ideal for applications that need to exchange modest amounts of data on a regular basis.
BLE is used extensively in healthcare, fitness, tracking, beacons, security, and home automation etc.
Bluetooth Low Energy is natively supported by mobile operating systems such as iOS, Android, and Windows Phone, as well as macOS, Linux, Windows 8 & 10.
ESP32 BLE
You can use ESP32 BLE either as a BLE server or a client.
Examples are available in the ESP32 BLE library(Arduino IDE) which you can use to implement BLE services.
Note:
The Arduino IDE must have the ESP32 board manager file and libraries installed. If you haven't previously prepared your Arduino IDE to operate with the ESP32, then read our previous tutorial, i.e., Introduction to ESP32 Programming Series.
BLE Server Code Description
For coding, we are using Arduino IDE’s inbuilt example and will make the required changes in that code only.
I will also explain the code in detail for beginners to understand.
In this code, ESP32, BLE will be used as a server.
Import the necessary/required libraries for the BLE application.
Define a UUID for the Service and Characteristic.
To generate UUIDs, go to the following link:
https://www.uuidgenerator.net/
You can either use the default UUIDs if you wish to or go to the above link to generate random UUIDs as per your services and attributes.
Call back or acknowledge the server whether the client is connected or not
Arduino Setup() Function
Serial Communication at a baud rate of 115200.
Create a name for your BLE device for identification, we named it Wibree.
Set the BLE device as a server.
Create a service for the BLE server with the UUID defined earlier.
The characteristic for that service is then set. As you can see, you're still using the UUID you created previously, and you'll need to supply the properties of the characters as arguments. It's read and write in this scenario.
You can also add other services like battery, indicate, notify etc.
The setValue() method can be used to set the value of a characteristic.
The above value can be changed to whatever you like. This could be a sensor reading.
Finally, activate the service and advertising so that other BLE devices can scan and locate this BLE device.
Arduino Loop() Function
Here we can check if the device is connected to the client or not
If connected then do some tasks like transmitting data or receiving input from the client.
Data Size Per Packet
20 bytes per packet.
Unfortunately, BLE isn't built to handle large amounts of data. The maximum data size per packet in the BLE specification is 20 bytes, so if you wish to communicate more, you'll have to divide it up into many packets. Fortunately, this isn't a challenging task. Simply put, use a delimiter like "!" or "*" or something unique at the end of your whole message to signal the app that the message is done and to start listening for future communications. If you want to send + > 20 bytes cumulatively, for example, you can send and then proceed with the next message if needed.
Testing ESP32 BLE Server
After creating a BLE server using ESP32, we can use a BLE application available on the Play store for testing purposes.
Demonstration with BLE scanner app:
Go to the play store
Search for the BLE scanner and download the app
After installing the app turn on the Bluetooth.
Open the app and search for nearby devices.
Now connect to ESP32 BLE by clicking on the ESP32 device.
In our case, we named the device ‘Wibree’.
Now you can use the various services provided by BLE like writing and reading data packets, checking battery levels etc. and a lot more.
This concludes the tutorial. I hope you find it helpful.
Hello readers, I hope you all are doing great. Today, we are going to start the second section of the ESP32 tutorial series and today's our first tutorial, where we will have a look at How to Create a Web Server with ESP32. In our previous tutorial, we introduced you to the basics of the ESP32 microcontroller. where we discuss How to set up Arduino IDE to program ESP32. In this tutorial, we will discuss creating a web server using the ESP32 module.
One of the most interesting features of the ESP microcontroller series is its wireless connectivity via WiFi & Bluetooth. Wireless connectivity protocols supported by ESP32 are:
A web server is software or hardware that stores, processes, and delivers web pages to users on request. In other words, it serves users all over the World Wide Web (www). The web server uses the hypertext transfer protocol (HTTP or HTTPS) for communication with the clients(normally, web browsers). We know that HTTP is a set of rules to format and exchange messages.
The following are some important features of a web server:
Features of a Web Server
A web server, either physical or virtual, is a computer that hosts one or more websites.
The HTTP protocol is the foundation of any data exchange within the network when using the server. So a web server uses it to communicate with the client.
The web server uses static content and the files do not change dynamically. Some such files used in a web service are:
HTML files
Images
Stylesheets
JavaScript files
The web server has multiple settings to avoid unnecessary attacks. This helps to maintain the health and integrity of a website. There are multiple types of web security attacks, such as:
DDoS attacks
SQL injection
Cross-site scripting (XSS)
Hence, a web server has multiple features to serve the users on the web.
Web Server & Client Communication
A client is an entity that initiates communication with the web
server and then the server provides the information required. In simple
words, the client is a program, device, or user that requests services
or resources from the devices, such as the web server. The communication
and relationship between these two is called the server-client model.
The following are the general server-client model steps that will help
to understand the whole scenario:
The client sends an HTTP request to the server. The request includes the URL of the web page that the client wants to retrieve.
The
client (when the user requires data) sends an HTTP request to the
server. This request may include the URL of the web page from which the
client wants to retrieve the information.
The server receives
the request instantly and processes it. It does it when it looks up the
URL saved in its database to find the corresponding web page file a
client requires.
If the web page file is found, the server sends
it back to the client in the form of an HTTP response. This response
also includes other important types of information, such as the page's
content type and expiration date, etc.
The client then receives
the response and renders the web page on the user's screen. The client
uses the content type information to determine how to display the web
page.
If the page is not found in the URL database, the server shows the error.
Web browsers like Chrome, Firefox, and Safari are examples of clients.
ESP32 as a Web Server
The ESP32 is a microcontroller famous for its wireless capabilities, which makes it ideal for a large number of fields, especially IoT. We are talking about WiFi connectivity as a web server and here are the key features of this module related to it:
The ESP32 is made under the IEEE 802.11b/g/n standards; therefore it has a 2.4 GHz frequency band. Therefore, it can be used as:
Common WiFi routers
Access point
The built-in WiFi capabilities of the ESP32 allow it to be used as a server and carry out the easiest and most effective communication at a distance without any physical connection.
It has three operating modes:
In station mode, the ESP32 is operated as a WiFi client. It means it can be connected to the existing Wi-Fi network. (We are covering today)
In access point mode, it is operated as a WiFi access point; therefore it allows other devices to create a connection with it. (will be covered in the next lecture)
In dual mode, it can act as a server and as a client and allow the features of both at the same time. (will be covered in the 3rd lecture of section 2)
It has a dual processor that helps in handling multiple tasks at the same time. Therefore, ESP32 is more capable of managing a large network of devices and making it responsive for concurrent connections.
It has asynchronous web server libraries, such as “ESPAsyncWebServe” to handle the HTTP requests asynchronously. These are useful because they allow it to effectively manage the connections without blocking the execution of other tasks.
ESP32 has multiple security protocols that are used when creating the web server. As a result, it provides secure and protective communication between the devices.
It has over-the-air updates, which means it can update the device's firmware without physically accessing it. It helps with remote updates and maintenance.
The ESP32 is suitable for use as a server because of its multiple features, including:
It can serve static files
It can handle different HTTP methods (GET, POST, etc.)
It supports features like server-side scripting
The WebSockets feature of ESP32 allows it to carry out bi-directional communication between servers and clients. You will learn about both of these in just a bit.
The ESP32 supports WiFi Direct, which is also referred to as the Peer to Peer (P2P); therefore, it can form a direct connection with other devices with no need for an external WiFi network.
ESP32 WebServer Working Principle
We know that the ESP32 has a built-in WiFi feature. This makes it suitable to use as a server. The example of the server-client relationship we have just discussed shows the internet connection of the whole world. The ESP32 can be used for the intranet connection, which is defined as:
"An intranet is a private network that has limited functionalities and is only accessible to users within a specific organization/location."
Usually, this network may consist of different devices, such as mobile phones, computers, laptops and tablets. The Arduino IDE is for the programming of the ESP32, just like we have done in the previous session. If your Arduino IDE is ready with the boards and ports, then let us try the built-in example of the ESP32 to use as a server.
What is an SSID?
An SSID is a service set identifier that is the unique name of a wireless local area network (WLAN).
It can be 32 characters long.
It may include numbers, letters, and signs.
The SSID can be set by the user as well.
In simple words, the SSID is the name of the WiFi connection people use for their connection.
In the experiment we are just performing, the user has to replace the SSID with their own SSID to connect with the ESP32.
Using the ESP32 Server Built-in Example
Using the ESP32 as a server is easy with the web server example. It has the basics, and here are the steps to follow:
Open the Arduino IDE.
Connect the esp32 to your system through the cable. Make sure the ESP32 is connected accurately.
Click on tools>boards>ESP32>Node32s. This is my board and you can choose according to the model of ESP32.
Go to the files> examples>examples of Nose32s>WiFi and from the side menu, choose “SimpleWifiServer".
It will create a new project with the code in it to run the ESP32 (connected to your system) as a server.
Press the encoder (EN) button of the ESP32.
Change the SSID and password according to your choice. In my case, it is PTCL-BB.
Go to lines 38, 103, and 106 by one and replace the pin “5” digit with pin “2” because the built-in light is at pin 2.
Replace lines 70 and 71 with the following:
client.print("Click <a href=\"/H\">here</a> to turn the LED on pin 2 on.<br>");
client.print("Click <a href=\"/L\">here</a> to turn turn the LED on pin 2 off.<br>");
All the instructions are given in the code. Go to line 30 and place your SSID there.
Go to line 31 and enter the password of your choice.
Read the code carefully and hit the “verify” button.
Once the code is compiled, press "Boot" on the ESP32 when the uploading process is carried out.
Wait for the loading to complete.
Click on the “Serial Monitor” button at the upper right corner of the screen to open the monitor. You can go to Tool>Serial Monitor for the same task.
Choose the baud rate of 115200 from the drop-down menu at the right corner of the monitor.
Right now, the monitor is blank:
Click the EN button on the EPS32 to see the information.
Now that the monitor has data and is loading, it starts to connect with the WiFi connection of the system.
Once the loading is complete, it will provide the IP address. Copy this address.
Go to the new tab in the browser and paste the address there.
You will see that merely placing the “H” or “L” just after the IP address (as given in the code comment) will turn on and off the LED on ESP32 according to the URL.
Note: Make sure you have installed the port and board before you try this code and have selected all the right options; otherwise, you can face errors.
ESP32 Server as Messenger
The ESP32 can be used to send the message through the browser.
The microcontroller connects to the internet connection of the system.
The serial monitor shows the IP address.
The ESP32 acts as a server and through the URL of the browser, the user will send the message to the Arduino IDE.
This message will be shown on the serial monitor.
The user can change the message through the URL pasted in the web browser.
Material Required
Internet connection
System (e,g, laptop)
ESP32 microcontroller
Connecting cable
Code for ESP32 as Server
#include <WiFi.h>
const char *ssid = "My-SSID";
const char *password = "My-Password";
WiFiServer server(80);
void setup() {
Serial.begin(115200);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(1000);
Serial.println("Connecting to WiFi...");
}
Serial.println("Connected to WiFi");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
server.begin();
}
void loop() {
WiFiClient client = server.available();
if (client) {
Serial.println("New Client.");
while (client.connected()) {
if (client.available()) {
String request = client.readStringUntil('\r');
client.flush();
// Check if the request contains a specific message
Make sure you have the respective port and board installed successfully.
Connect the right port and board.
Paste the code given above into the new project.
"Verify" the code by using the button.
Once verified, compile and upload the code.
Once the code is compiled, press the Boot button.
Once the installation is completed, go to the serial monitor.
Press the EN button.
The serial monitor will show the information. Copy the IP address shown on the end of loading.
The general ULR for sending the message through the server is given as: http://esp32-ip-address/message?message=Hello
To send the “Hello” message to the ESP32 through the browser, use your IP address and the message. In my case, I am pasting the following URL in the browser: http://192.168.43.251/message?message=Hello
Once reloaded, go to the serial monitor and check for the message:
For the demonstration purpose, we will create a webpage and will launch it through our ESP32 module, so ESP32 will be acting as a web server, serving the page.
This webpage will have 3 Buttons on it, which will be controlling three LEDs, we will turn ON or OFF respective LEDs using these buttons.
WebServer Page is shown in the below figure:
Now the question arises, how will ESP32 understand which Button has been pressed?
For that, we have created multiple links i.e. the HomePage Url will look like:
http://192.168.43.188/
When a user will click on LED 26 ON Button, we will redirect the user to:
http://192.168.43.188/26/on
Now, when the client wants to turn OFF the LED, we will redirect to:
http://192.168.43.188/26/off
So, actually, we are checking the request from the client and based on that request we are turning ON or OFF the respective LED.
Moreover, we are providing the same webpage to all the links but with the change in the state of each button i.e. if it's ON then Blue, otherwise Green.
If it looks too complicated, don't worry. These things will get more clear when we will cover the Arduino coding.
ESP32 Wi-Fi module includes a number of useful characteristics, including the ability to use a soft access point mode, a station mode, or both modes at the same time. Only station mode will be discussed in this session. I'll also cover how to use this board in soft access mode in future tutorials.
Station Mode: The ESP32 board connects to your Wi-Fi network via a router in Station mode. The router serves as the communication channel between the web client and the ESP32. The IP address is obtained from the Wi-Fi router. Web clients can connect to the Web server using this IP address across a local network.
Access Point Mode: In this mode, the ESP32 creates its own wireless Wi-Fi network, similar to the one provided by your existing router. We don't need to connect the ESP2 to a Wi-Fi network in this mode. This Wi-Fi board can link up to 5 devices to the Wifi network it creates.
Controlling peripherals Using ESP32 Web Server
Connect the peripherals to the ESP32 board which you want to control through the ESP32 Web Server.
Here, we are going to control two external LEDs connected to LED1 (GPIO 26), LED2 (GPIO 27), and an inbuilt LED.
The following are the requirements for creating an ESP32 webserver to control peripherals:
ESP32 module
Internet connection
LEDs
Resistors
Connecting Wires
Arduino IDE Code
Using the Arduino IDE, upload the following code to the ESP32 module:
#include
// Replace with your network credentials
char* ssid = "ESP32"; //enter SSID
char* passphrase = "asdfgf@123"; // enter the password
// Set web server port number to 80
WiFiServer server(80);
// Variable to store the HTTP request
String header;
// Auxiliar variables to store the current output state
String output26State = "off";
String output27State = "off";
String builtin_led_state = "off";
// Assign output variables to GPIO pins
const int output26 = 26;
const int output27 = 27;
// Current time
unsigned long currentTime = millis();
// Previous time
unsigned long previousTime = 0;
// Define timeout time in milliseconds (example: 2000ms = 2s)
const long timeoutTime = 2000;
void setup() {
Serial.begin(115200);
// Initialize the output variables as outputs
pinMode(output26, OUTPUT);
pinMode(output27, OUTPUT);
pinMode(LED_BUILTIN, OUTPUT);
// Set outputs to LOW
digitalWrite(output26, LOW);
digitalWrite(output27, LOW);
digitalWrite(LED_BUILTIN, LOW);
// Connect to Wi-Fi network with SSID and password
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, passphrase);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
// Print local IP address and start web server
Serial.println("");
Serial.println("WiFi connected.");
Serial.println("IP address: ");
Serial.println(WiFi.localIP());
server.begin();
}
void loop(){
WiFiClient client = server.available(); // Listen for incoming clients
if (client) {
// If a new client connects,
currentTime = millis();
previousTime = currentTime;
Serial.println("New Client."); // print a message out in the serial port
String currentLine = ""; // make a String to hold incoming data from the client
while (client.connected() && currentTime - previousTime <= timeoutTime) { // loop while the client's connected
currentTime = millis();
if (client.available()) { // if there's bytes to read from the client,
char c = client.read(); // read a byte, then
Serial.write(c); // print it out the serial monitor
header += c;
if (c == '\n') { // if the byte is a newline character
// if the current line is blank, you got two newline characters in a row.
// that's the end of the client HTTP request, so send a response:
if (currentLine.length() == 0) {
// HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
// and a content-type so the client knows what's coming, then a blank line:
client.println("HTTP/1.1 200 OK");
client.println("Content-type:text/html");
client.println("Connection: close");
client.println();
// turns the GPIOs on and off
if (header.indexOf("GET /26/on") >= 0)
{
Serial.println("GPIO 26 on");
output26State = "on";
digitalWrite(output26, HIGH);
}
else if (header.indexOf("GET /26/off") >= 0)
{
Serial.println("GPIO 26 off");
output26State = "off";
digitalWrite(output26, LOW);
}
else if (header.indexOf("GET /27/on") >= 0)
{
Serial.println("GPIO 27 on");
output27State = "on";
digitalWrite(output27, HIGH);
}
else if (header.indexOf("GET /27/off") >= 0)
{
Serial.println("GPIO 27 off");
output27State = "off";
digitalWrite(output27, LOW);
}
else if (header.indexOf("GET /LED_BUILTIN/on") >= 0)
{
Serial.println("BUILTIN LED on");
builtin_led_state = "on";
digitalWrite(LED_BUILTIN, HIGH);
}
else if (header.indexOf("GET /LED_BUILTIN/off") >= 0)
{
Serial.println("BUILTIN_LED off");
builtin_led_state = "off";
digitalWrite(LED_BUILTIN, LOW);
}
// Display the HTML web page
client.println("");
client.println("");
client.println("");
// CSS to style the on/off buttons
// Feel free to change the background-color and font-size attributes to fit your preferences
client.println("");
// Web Page Heading
client.println("
ESP32 Web Server
");
// Display current state, and ON/OFF buttons for builtin led
client.println("
LED_BUILTIN - State " + builtin_led_state + "
");
// If the LED is off, it displays the ON button
if (builtin_led_state=="off")
{
client.println("
");
}
else
{
client.println("
");
}
// Display current state, and ON/OFF buttons for GPIO 26
client.println("
LED_1 - State " + output26State + "
");
// If the output26State is off, it displays the ON button
if (output26State=="off")
{
client.println("
");
}
else
{
client.println("
");
}
// Display current state, and ON/OFF buttons for GPIO 27
client.println("
LED_2 - State " + output27State + "
");
// If the output27State is off, it displays the ON button
if (output27State=="off")
{
client.println("
");
}
else
{
client.println("
");
}
client.println("");
// The HTTP response ends with another blank line
client.println();
// Break out of the while loop
break;
} else { // if you got a newline, then clear currentLine
currentLine = "";
}
} else if (c != '\r') { // if you got anything else but a carriage return character,
currentLine += c; // add it to the end of the currentLine
}
}
}
// Clear the header variable
header = "";
// Close the connection
client.stop();
Serial.println("Client disconnected.");
Serial.println("");
}
}
Note:
You need to modify the SSID and password with your network credentials.
Code Description:
Here, we'll take a closer look at the code to see how it works.
The first task is to add a Wi-Fi library.
As mentioned previously, you must type your SSID and password inside the double quotes in the following lines.
As we are creating a web server, so we need to assign a port to it and normally we use port 80 for a local webserver.
So, in the below code, Port 80 is assigned to the webserver and then initialized a few variables:
String header: variable to store the header of the HTTP request.
Below the header variable, we have variables to store the current state of connected peripheral LEDs and built-in LED. If you wish to add more peripherals and save their states, you need to create more variables. By default, all LEDs are in the OFF state.
Next, assigned GPIOs to each peripheral device or component. Here we are using GPIO 26(LED1) and GPIO 27(LED2). You can use any other suitable GPIOs.
Lastly, we have initialized a few variables to check the connection timeout, we will check their working soon.
Arduino Setup() Function
Now let's first have a look at the Arduino setup loop.
First, we have initialized our Serial Port at a baud rate of 115200, so that we could monitor the results at the serial terminal.
Define the GPIOs as OUTPUTs and set them to LOW, as by default LEDs will be off.
To set up a wifi connection, we called the WiFI.begin() and here we have provided our SSID and passphrase as variables.
Now our ESP32 will try to connect to the provided WiFi connection.
As you can see, we have a while loop, where we are checking the WiFi Status.
If ESP32 gets connected with WiFi, the while loop will break and a message will get printed on the Serial Monitor "WiFi Connected".
Now our ESP32 is connected to the WiFi, so the router must have assigned an IP address to ESP32 and we are printing it on Serial using WiFi local IP Function.
Finally, we begin our server, to which we have assigned Port 80 at the start.
Arduino Loop() Function
Now, we are done with all the basic settings in the setup function. Let's have a look at the code in the Loop function:
At the last line of the Setup function, we have started our webserver, so now ESP32 is acting as a webserver and is waiting for incoming clients.
But what will happen, when someone will hit the IP Address of this webserver?
So, in the loop function, first of all, we are listening to the incoming client using the server.available() function.
If any client is available i.e. someone has entered our IP Address in the browser then we will print the HTML page.
So, we are going to write the rest of our code in this IF loop.
AS you can see in the below code, if the client is available, we have printed "New Client" on Serial Monitor.
After that, we have a while loop checking for client connection, so as long as we have a connection with the client, we will remain in this loop.
Inside this while loop, we have an If loop, checking if the client is available.
Now, if we are connected to the client, we need to read for the incoming request.
So, If there are any bytes to read from the client, read those bytes:
The client request ends at New Line Character \n, so we are checking for that.
Once we received the New Line Character, we are sending the response back to the Client.
In response, we have first sent the HTTP header, which is the default for webpages so that browsers should understand the response type.
Checking Request Type
As we discussed earlier, on each button press, we are redirecting our client to its respective link.
Depending on which button is pushed, we make requests to different URLs to turn the LEDs on and off using if else statements, as shown below:
As you can see in the above code, we are repeating the same code three times for 3 LEDs.
In the first block, we are simply checking the header response and if it's a GET request and from "/26/on", we have turned that Pin HIGH, changed the LED state variable to "on" and sent a message on the serial monitor.
So, if a client clicks on the LED 26 ON button, ESP32 will understand the GET request and glow the LED.
The other buttons work in the same way. If you wish to add more outputs, you'll need to change this section of the code.
HTML to display a web page
We have designed the output part i.e. what we are going to do when a user clicks any button.
And now we are going to design those buttons themselves i.e. we are designing the webpage.
As you can see in the below figure, we have standard HTML tags at the start.
After that, we have some CSS text to design the buttons and the appearance of the web page. We use the Helvetica font and set the information to be shown as a block with the center aligned.
Next, displaying Web page heading i.e. "ESP32 Web Server".
Next, comes the If Loop for the first Button, we are checking the LED state variable and based on LED state, we are displaying our Button.
So, if the LED state is OFF, we are redirecting the user to /LED_BUILTIN/on and vice versa.
That's how we are changing the Buttons on the webpage, as you can see buttons are using different CSS classes for on and off states.
Similar loops are used to display the states on other connected LEDs.
Finally, we are closing the web connection and clearing the header that was used to store the HTTP request header using client.stop() function.
Printing information about the closed web connection on the serial monitor.
Uploading Web Server Code to ESP32
Please reread the previous instruction, "Introduction to ESP32 programming series," if you are unfamiliar with the procedure of uploading code in the Arduino IDE.
After uploading the code, open the Serial Monitor with a baud rate of 115200.
Enable the ESP32 by pressing the EN (enable) button. The ESP32 establishes a Wi-Fi connection and the Serial Monitor displays the ESP32 IP address. To connect to the ESP32 web server, you'll need that IP address.
Note:
Make sure you have selected the right board and COM port.
Getting IP address and Access ESP32 web Server
After successfully uploading the code in esp32 module.
Open Serial Monitor from the top right corner of Arduino IDE screen as shown in figure below:
The IP address required to connect to the ESP32 point will be displayed on the Serial Monitor. It's 192.168.43.223 in this scenario.
To access the webserver, type the IP Address of the ESP32 into a Web Browser on a laptop or a mobile phone. It's 192.168.43.223 in our case.
You should be able to see a simple web page served by the ESP32's Web Server if everything goes well.
A screenshot of a Web Browser on a laptop accessing the ESP32 Web Server is shown below.
The image below is displaying the ONstate of the inbuilt LED.
The inbuilt LED is Blue in color.
The below image is displaying the OFF State of the inbuilt LED
Hence, We have done a lot of work on the ESP32 by using it as a server. In the beginning, we saw what is a web server and studied its features in detail. After that, we saw that ESP32 can be used as a server and we saw the feature that makes it ideal for this task. Then we experimented to learn the concept, in which we saw the built-in example of ESP32 as a server in Arduino IDE. We saw the step-by-step procedure to experiment and once it was completed, we moved on to a more complex example. I hope you find this tutorial useful and have performed it by yourself but if you are stuck at any point, you can ask in the comment section.
Using the ESP32 web server and the preceding process, you can control the peripherals linked to the ESP32 module from any mobile, tablet, or computer. The only need is that all of the devices to be linked to the same network.
This concludes the lesson. I hope it becomes useful to you. In the next tutorial, we will have a look at How to work the ESP32 BLE, so stay tuned. Have a good day. :)
Syed Zain Nasir
I am Syed Zain Nasir, the founder of <a href=https://www.TheEngineeringProjects.com/>The Engineering Projects</a> (TEP). I am a programmer since 2009 before that I just search things, make small projects and now I am sharing my knowledge through this platform.I also work as a freelancer and did many projects related to programming and electrical circuitry. <a href=https://plus.google.com/+SyedZainNasir/>My Google Profile+</a>