SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 UNO - MySQL

Want every reading from your board stored in a real database? Log data from the ESP32 Uno into MySQL with one WiFi request and a tiny PHP file. The ESP32 Uno form board calls a web page on your PC, and that page writes the value into a MariaDB table. The same pattern lets you change rows or pull them back out later.

What you will do:

Set up Apache, PHP and a MySQL server on your PC with XAMPP
Make a local-only database account, a database and a table
Write a PHP file that saves a temperature value
Send that value from the ESP32 Uno with an HTTP GET call

Components You Need

1	×	ESP32 Uno-form Board
1	×	USB Cable Type-A to Type-C (for USB-A PC)
1	×	USB Cable Type-C to Type-C (for USB-C PC)
1	×	Optionally, DC Power Jack
1	×	Breadboard
1	×	Jumper Wires

Or you can buy the following kits:

DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables .

Two Ways to Reach a MySQL Database

By the end of this part, you know which link type to use and why.

People new to databases often mix up the MySQL Database and the MySQL server. The server is the running program. The database is the set of tables it looks after. For this project, you can treat both words as one idea.

Method	How the Board Talks	Used Here
Direct	The ESP32 Uno opens a MySQL protocol session with the server	No
Indirect	The ESP32 Uno calls a web page, and PHP on the server runs the SQL	Yes

Direct Link from the ESP32 Uno to the MySQL Server

It sounds shorter, but the direct link has costs you should not accept on a small board.

Weak Point	What Goes Wrong
Remote login	A database user must accept logins from other network devices, which is a security hole even with few rights
Board load	The sketch must hold SQL text and decode MySQL packets, so it eats RAM and CPU time
Big replies	One SELECT can send back more data than the board can hold, and it crashes
Raw data	The server gets unprocessed values, so the SQL side grows more complex
No TLS	Most microcontroller MySQL libraries skip encryption, so the login travels as plain text

Indirect Link through a Web Server (HTTP/HTTPS)

A PHP page in the middle removes every weak point above. The board only sends a short web request, and the PC does the database work.

How It Works

The ESP32 Uno adds the value to the URL of an HTTP/HTTPS request and sends it to the web server.
Apache starts the matching PHP script.
The script takes the value out of the request, builds the SQL and runs it on the MySQL database.
The script answers with one short line, and the board reads it in the HTTP response.

Here, XAMPP runs everything on your own PC. The same files also work on a rented server or a cloud machine such as AWS EC2.

Benefit	Reason
Safer login	Apache and MySQL share one machine, so the database account can be locked to localhost
Secret stays home	The database password lives in the PHP file on the server, never in the sketch
Light sketch	PHP does the data work, so the board code stays short
No memory crash	PHP returns only the few bytes the board needs
Encryption ready	The ESP32 Uno can make HTTPS calls, so the data can travel encrypted

Good to know: if you add a login between the board and the web server, give it a different username and password from the MySQL account.

Build the Server Side

By the end of this part, your PC accepts a URL and saves its value as a table row.

Work through these steps in order and test after each one. If a step fails, you then know exactly where to look.

Step	Job	Result
1	Install XAMPP	MySQL, Apache and PHP on your PC
2	Make a database user	An account that only works from localhost
3	Make a database	An empty container for your tables
4	Make a table	A place for the temperature rows
5	Write a PHP script	A URL that inserts a value
6	Write the ESP32 Uno code	The board calls that URL

Step 1 — Install XAMPP

XAMPP bundles the MySQL server, the Apache web server and PHP in one installer.

Download XAMPP from this link and run the installer.
Check that C:\xampp\htdocs now exists. Every PHP file for this project goes in there.
Open the XAMPP Control Panel.
Press Start on the MySQL row and on the Apache row, as in the picture.

Step 2 — Make a Database User

This account can log in only from the PC itself. A stranger who learns the password still cannot reach the database from another machine, but PHP on the same PC can.

This guide uses the username esp32_uno_user and the placeholder password YOUR_DB_PASSWORD. Pick your own strong password.

Open a Command Prompt window and leave it open for the rest of the guide.
Move into the MySQL tools folder:

cd C:\xampp\mysql\bin

Command Prompt

C:\Users\YOUR_USER>cd C:\xampp\mysql\bin C:\xampp\mysql\bin>

A fresh install leaves the root account with no password. Close that gap now (swap in your own value for YOUR_ROOT_PASSWORD):

mysqladmin -u root password YOUR_ROOT_PASSWORD

Command Prompt

C:\xampp\mysql\bin>mysqladmin -u root password YOUR_ROOT_PASSWORD C:\xampp\mysql\bin>

mysql.exe -u root -p

Enter the root password, then press Enter.

Command Prompt

C:\xampp\mysql\bin>mysql.exe -u root -p Enter password: ****************** Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 9 Server version: 10.4.6-MariaDB mariadb.org binary distribution Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. MariaDB [(none)]>

Paste these three lines to create the account and give it rights:

CREATE USER 'esp32_uno_user'@'localhost' IDENTIFIED BY 'YOUR_DB_PASSWORD'; GRANT ALL PRIVILEGES ON *.* TO 'esp32_uno_user'@'localhost' WITH GRANT OPTION; FLUSH PRIVILEGES;

Command Prompt

MariaDB [(none)]> CREATE USER 'esp32_uno_user'@'localhost' IDENTIFIED BY 'YOUR_DB_PASSWORD'; Query OK, 0 rows affected (0.005 sec) MariaDB [(none)]> GRANT ALL PRIVILEGES ON *.* TO 'esp32_uno_user'@'localhost' WITH GRANT OPTION; Query OK, 0 rows affected (0.005 sec) MariaDB [(none)]> FLUSH PRIVILEGES; Query OK, 0 rows affected (0.001 sec) MariaDB [(none)]>

Note the username and password somewhere safe. The PHP file in Step 5 needs both.

Step 3 — Make a Database

Run this line to create a database called db_esp32_uno:

CREATE DATABASE db_esp32_uno CHARACTER SET = 'utf8' COLLATE = 'utf8_general_ci';

Command Prompt

MariaDB [(none)]> CREATE DATABASE db_esp32_uno CHARACTER SET = 'utf8' COLLATE = 'utf8_general_ci'; Query OK, 1 row affected (0.003 sec) MariaDB [(none)]>

Step 4 — Make a Table

The table tbl_temp has two columns.

Column	Type	Job
temp_id	INT UNSIGNED, AUTO_INCREMENT	Row number that MySQL fills in by itself
temp_value	FLOAT	The temperature the board sends

Paste these lines into the Command Prompt:

USE db_esp32_uno; CREATE TABLE tbl_temp ( temp_id INT UNSIGNED NOT NULL AUTO_INCREMENT, temp_value FLOAT DEFAULT 0.00, PRIMARY KEY (temp_id) );

Command Prompt

MariaDB [(none)]> USE db_esp32_uno; Database changed MariaDB [db_esp32_uno]> MariaDB [db_esp32_uno]> CREATE TABLE tbl_temp ( -> temp_id INT UNSIGNED NOT NULL AUTO_INCREMENT, -> temp_value FLOAT DEFAULT 0.00, -> PRIMARY KEY (temp_id) -> ); Query OK, 0 rows affected (0.044 sec) MariaDB [db_esp32_uno]>

Step 5 — Write the PHP Script

This file links the board to the database. It looks for a temperature field in the URL and stores it as a fresh row. Open Notepad, Notepad++ or any plain text editor and save the code below as insert_temp.php.

<?php if(isset($_GET["temperature"])) { $temperature = $_GET["temperature"]; // read the value sent in the URL $servername = "localhost"; $username = "esp32_uno_user"; $password = "YOUR_DB_PASSWORD"; $database_name = "db_esp32_uno"; // open a link from PHP to the local MySQL server $connection = new mysqli($servername, $username, $password, $database_name); // stop here if the login failed if ($connection->connect_error) { die("MySQL connection failed: " . $connection->connect_error); } $sql = "INSERT INTO tbl_temp (temp_value) VALUES ($temperature)"; if ($connection->query($sql) === TRUE) { echo "New record created successfully"; } else { echo "Error: " . $sql . " => " . $connection->error; } $connection->close(); } else { echo "temperature is not set in the HTTP request"; } ?>

Put the file in C:\xampp\htdocs.
Find the local IPv4 address of your PC. On Windows, type ipconfig in the Command Prompt and read the "IPv4 Address" line.
In a browser on the same PC, open http://192.168.0.19/insert_temp.php?temperature=25.3. Swap 192.168.0.19 for the address you found.
A short success line should appear:

Confirm the row really landed in the table:

SELECT * from tbl_temp;

Command Prompt

MariaDB [db_esp32_uno]> SELECT * from tbl_temp; +---------+------------+ | temp_id | temp_value | +---------+------------+ | 1 | 25.3 | +---------+------------+ 1 row in set (0.001 sec) MariaDB [db_esp32_uno]>

Row 1 holds 25.3, so the server side is done. Now the board only has to call the same URL.

ESP32 Uno Pinout

No wire goes to any header in this project, because the board uses its own WiFi radio. Keep the diagram below for later, when you add a real sensor and need the GPIO number behind each Uno label.

Step 6 — Write the ESP32 Uno Code

This sketch joins your WiFi, calls insert_temp.php once with a fixed 30.5°C and prints the server answer. It uses WiFi.h and HTTPClient.h, which ship with the esp32 by Espressif Systems core, so there is nothing extra to install.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-mysql */ #include <WiFi.h> #include <HTTPClient.h> const char WIFI_SSID[] = "YOUR_WIFI_SSID"; const char WIFI_PASSWORD[] = "YOUR_WIFI_PASSWORD"; String HOST_NAME = "http://192.168.0.19"; // put the local IP address of the PC that runs XAMPP here String PATH_NAME = "/insert_temp.php"; String queryString = "?temperature=30.5"; void setup() { Serial.begin(9600); WiFi.begin(WIFI_SSID, WIFI_PASSWORD); Serial.println("Connecting"); while(WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); } Serial.println(""); Serial.print("Connected to WiFi network with IP Address: "); Serial.println(WiFi.localIP()); HTTPClient http; http.begin(HOST_NAME + PATH_NAME + queryString); // plain HTTP, no TLS int httpCode = http.GET(); // a value below zero means the ESP32 Uno could not reach the server if(httpCode > 0) { // the server answered the request if(httpCode == HTTP_CODE_OK) { String payload = http.getString(); Serial.println(payload); } else { // the server replied, but not with 200 OK Serial.printf("[HTTP] GET... code: %d\n", httpCode); } } else { Serial.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str()); } http.end(); } void loop() { }

Upload and Test

First time with this board? Set it up with ESP32 Uno - Getting Started before you continue.
Keep the server running: Apache and MySQL must both show green in the XAMPP Control Panel.
Plug in the USB Type-C cable between the ESP32 Uno and your computer.
Select the board in Arduino IDE: pick ESP32 Dev Module and the COM port of the board (CH340).
Paste the sketch into a new Arduino IDE window.
Fill in your WiFi: put your network name and password in place of YOUR_WIFI_SSID and YOUR_WIFI_PASSWORD.
Point it at your PC: change 192.168.0.19 in HOST_NAME to the IPv4 address from Step 5.
Upload the sketch with the arrow button.
Open the Serial Monitor at 9600 baud.
Pro tip: give your PC a fixed (reserved) IP address in your router settings. Then HOST_NAME keeps working after the PC restarts.

Newbiely | Arduino IDE 2.3.8

──

☐

Newbiely.ino

···

8 Serial.println("Hello World!");

Output

Serial Monitor

Message (Enter to send message to 'ESP32 Dev Module' on 'COM15')

New Line

9600 baud

Connecting ......... Connected to WiFi network with IP Address: 192.168.0.42 New record created successfully

Ln 11, Col 1

ESP32 Dev Module on COM15

Check the table one more time:

SELECT * from tbl_temp;

Command Prompt

MariaDB [db_esp32_uno]> SELECT * from tbl_temp; +---------+------------+ | temp_id | temp_value | +---------+------------+ | 1 | 25.3 | | 2 | 30.5 | +---------+------------+ 2 rows in set (0.000 sec) MariaDB [db_esp32_uno]>

Row 2 came from the ESP32 Uno. Press the board's EN (reset) button and a third row with 30.5 appears.

Video Tutorial

See the ESP32 Uno build in action in the video below.

Code Explanation

By the end of this part, you can find the line to change for each job.

Code Part	What It Does
WIFI_SSID / WIFI_PASSWORD	Hold the name and password of your 2.4 GHz network
HOST_NAME + PATH_NAME + queryString	Join into the full URL, for example http	//192.168.0.19/insert_temp.php?temperature=30.5
WiFi.begin() and the while loop	Start the WiFi link and print a dot every 500 ms until it is up
http.begin() and http.GET()	Open the URL and send the GET request
httpCode check	Prints the PHP reply on 200 OK, the code number on other replies, or the error text when the server cannot be reached
http.end()	Frees the connection

All the work sits in setup(), so the board sends exactly one value per reset, and loop() stays empty.

ESP32 Uno vs UNO R4 for This Project

Moving this database logger from the UNO R4 WiFi to the ESP32 Uno mainly changes the network code.

Item	Arduino UNO R4 WiFi	ESP32 Uno
Logic voltage	5V	3.3V
WiFi library	WiFiS3.h	WiFi.h (built into the core)
HTTP code	Raw WiFiClient lines for the header	HTTPClient with http.GET()
Serial output	Full HTTP header plus body	Only the PHP reply line
Header pins used	None	None
Arduino IDE board	Arduino UNO R4 WiFi	ESP32 Dev Module

No wiring is needed on either board. The PHP file, the database and the table stay exactly the same, so only the sketch changes.

Change, Read or Delete Rows

Inserting is only one job. To update or read data, the ESP32 Uno sends the same kind of request, and only the SQL inside the PHP file changes.

Goal	SQL in the PHP File	Example URL
Add a row	INSERT INTO tbl_temp ...	insert_temp.php?temperature=30.5
Change a row	UPDATE tbl_temp SET temp_value=... WHERE temp_id=...	update_temp.php?id=2&temperature=29.1
Read the last value	SELECT temp_value FROM tbl_temp ORDER BY temp_id DESC LIMIT 1	get_temp.php
Remove a row	DELETE FROM tbl_temp WHERE temp_id=...	delete_temp.php?id=1

For a full PHP and MySQL reference, see W3Schools. For a read script, keep the answer short (one number or a few lines), and print it with http.getString() on the board.

Make It Safer

This guide keeps the setup small on purpose. Before you put it on the internet, add these upgrades:

Upgrade	Why
HTTPS with WiFiClientSecure	Encrypts the value and any login on the way
Basic access authentication	Stops strangers from writing rows to your table
Prepared statements in PHP	Blocks SQL injection through the URL
JSON and a REST style API	Makes larger data sets easy to send and check

More on logins: Basic access authentication.

Try These Next

Send a real reading from a DHT22 sensor on the ESP32 Uno instead of the fixed 30.5.
Log a DS18B20 value, as in ESP32 Uno - Temperature Sensor.
Move the request into loop() and post a value every 60 seconds.
Add a second column, such as humidity, and pass two fields in the URL.
Show the latest rows on a page served by the board itself, starting from ESP32 Uno - Web Server.

Troubleshooting

Problem	Possible Cause	Solution
No COM port appears in Arduino IDE	CH340 driver missing or a charge-only cable	Install the CH340 driver and use a USB cable that carries data
"Failed to connect" or "Waiting for download" during upload	The board did not enter download mode	Hold the BOOT button while the upload starts, then let go
Endless dots after "Connecting"	Wrong SSID or password, or the router only offers 5 GHz	Check spelling and case, and join a 2.4 GHz network
"[HTTP] GET... failed, error - connection refused"	Apache stopped, wrong IP in HOST_NAME, or Windows firewall blocks port 80	Start Apache, use the PC IPv4 address and allow Apache through the firewall
Reply says "MySQL connection failed"	MySQL stopped, or the user, password or database name in PHP is wrong	Start MySQL in XAMPP and compare insert_temp.php with Steps 2 and 3
"[HTTP] GET... code - 404"	insert_temp.php is not in htdocs or PATH_NAME is misspelled	Move the file into C\xampp\htdocs and check the file name
Reply says "temperature is not set in the HTTP request"	The query string is missing	Make sure the URL ends with ?temperature= and a number
It worked yesterday but fails today	The PC got a new IP address from the router	Read the IP again with ipconfig, or reserve a fixed IP for the PC
Board reboots while sending	Weak USB port or long thin cable	Use a short cable and a powered USB port or the DC jack

FAQ

Does the ESP32 Uno need an extra WiFi shield to log data to MySQL?

No. The WiFi radio is part of the ESP32 Uno chip. You only need the board, a USB cable and a computer or server that runs MySQL, Apache and PHP.

Why use a PHP page instead of a MySQL library on the board?

A PHP page keeps the database password off the board and lets you lock the MySQL account to localhost. The sketch only sends one URL, so it stays small. MySQL libraries for microcontrollers are heavier and often have no encryption.

Is MariaDB in XAMPP the same as MySQL?

For this project, yes. MariaDB is a fork of MySQL and accepts the same SQL commands and the same PHP mysqli code.

Can the PHP script run on a web host instead of my PC?

Yes. Upload insert_temp.php to any host with PHP and MySQL, make the database there, and change HOST_NAME to the host address. Use HTTPS and a login on a public server.

How do I log a value every few minutes instead of once?

Move the HTTPClient part from setup() into loop() and add a delay() or a millis() timer. Build the query string from your sensor value each time, for example with String(value).

Which ESP32 Uno pins can read an analog sensor while WiFi is on?

Use A2 to A5 (GPIO35, GPIO34, GPIO36, GPIO39). A0 (GPIO2) and A1 (GPIO4) sit on ADC2, and analogRead() on ADC2 does not work while WiFi is running. The ESP32 Uno ADC returns 0 to 4095, not 0 to 1023.

My UNO R4 WiFi sketch for MySQL does not compile on the ESP32 Uno. Why?

The UNO R4 WiFi sketch includes WiFiS3.h and calls WiFi.firmwareVersion(), which exist only for that board. The ESP32 Uno uses WiFi.h and HTTPClient.h from the esp32 core, as in the code above. The PHP and database parts do not change.

Do I need a driver before Arduino IDE can see the ESP32 Uno?

Usually yes on Windows. The ESP32 Uno uses a CH340 USB-to-serial chip. Install the CH340 driver once, then a new COM port appears when you plug in the board.

What if my project needs more pins than the Uno headers give?

The ESP32 Uno has a few extra holes near the power header: GPIO32 and GPIO33 (I/O, PWM, analog on ADC1, so they also work while WiFi is on) and GPIO15 (I/O, PWM, analog on ADC2). Solder pin headers to them and write the GPIO number in your code. For a WiFi data logger, put extra analog sensors on GPIO32 or GPIO33. Two warnings. First, GPIO15 and GPIO0 (the IO0 pin at the unused Uno NC position) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code, so use GPIO32/33 first. Second, never use the six holes under the digital header (SD0 to SD3, CMD, CLK = GPIO6 to GPIO11). They are wired to the flash chip, and using them crashes the board.

Can I see the logged values on my phone?

Yes. Write a small PHP page that runs a SELECT and prints the rows as an HTML table, then open it in the phone browser on the same network. For a public view, move the files to a web host.

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