ESP32 Data Logging to Firebase Realtime Database

In this guide, you’ll learn how to log data with the ESP32 to the Firebase Realtime Database with timestamps (data logging) so that you have a record of your data history. As an example, we’ll log temperature, humidity, and pressure from a BME280 sensor and we’ll get timestamps from an NTP server. Then, you can access the data using the Firebase console, or build a web app to display the results ().

Part 2:

Other Firebase Tutorials with the ESP32/ESP8266 that you might be interested in:

What is Firebase?

Firebase is Google’s mobile application development platform that helps you build, improve, and grow your app. It has many services used to manage data from any android, IOS, or web application like , , , etc.

Project Overview

The following diagram shows a high-level overview of the project we’ll build.

1. The ESP32 authenticates as a user with email and password (that user must be set on the Firebase authentication methods);
2. After authentication, the ESP gets the user UID;
3. The database is protected with security rules. The user can only access the database nodes under the node with its user UID. After getting the user UID, the ESP can publish data to the database;
4. The ESP32 gets temperatrure, humidity and pressure from the BME280 sensor.
5. It gets epoch time right after gettings the readings (timestamp).
6. The ESP32 sends temperature, humidity, pressure and timestamp to the database.
7. New readings are added to the database periodically. You’ll have a record of all readings on the Firebase realtime database.

These are the main steps to complete this project:

You can continue with the Firebase project tutorial or create a new project. If you use the Firebase project of that previous tutorial, you can skip to section because the authentication methods are already set up.

Preparing Arduino IDE

For this tutorial, we’ll program the ESP32 board using the Arduino core. So, make sure you have the ESP32 add-on installed in your Arduino IDE:

If you want to program the ESP boards using VS Code with the PlatformIO extension, follow the following tutorial instead:

1) Create Firebase Project

1) Go to and sign in using a Google Account.

2) Click Get Started and then Add project to create a new project.

3) Give a name to your project, for example, ESP Firebase Demo.

4) Disable the option Enable Google Analytics for this project as it is not needed and click Create project.

5) It will take a few seconds to set up your project. Then, click Continue when it’s ready.

6) You’ll be redirected to your Project console page.

2) Set Authentication Methods

To allow authentication with email and password, first, you need to set authentication methods for your app.

“Most apps need to know the identity of a user. In other words, it takes care of logging in and identifying the users (in this case, the ESP32). Knowing a user’s identity allows an app to securely save user data in the cloud and provide the same personalized experience across all of the user’s devices.” To learn more about the authentication methods, you can .

1) On the left sidebar, click on Authentication and then on Get started.

2) Select the Option Email/Password.

3) Enable that authentication method and click Save.

4) The authentication with email and password should now be enabled.

5) Now, you need to add a user. On the Authentication tab, select the Users tab at the top. Then, click on Add User.

6) Add an email address for the authorized user. It can be your google account email or any other email. You can also create an email for this specific project. Add a password that will allow you to sign in to your app and access the database. Don’t forget to save the password in a safe place because you’ll need it later. When you’re done, click Add user.

7) A new user was successfully created and added to the Users table.

Notice that Firebase creates a unique UID for each registered user. The user UID allows us to identify the user and keep track of the user to provide or deny access to the project or the database. There’s also a column that registers the date of the last sign-in. At the moment, it is empty because we haven’t signed in with that user yet.

3) Get Project API Key

To interface with your Firebase project using the ESP32 board, you need to get your project API key. Follow the next steps to get your project API key.

1) On the left sidebar, click on Project Settings.

2) Copy the Web API Key to a safe place because you’ll need it later.

4) Set up Realtime Database

Now, let’s create a realtime database and set up database rules for our project.

1) On the left sidebar, click on Realtime Database and then click on Create Database.

2) Select your database location. It should be the closest to your location.

3) Set up security rules for your database. You can select Start in test mode. We’ll change the database rules in just a moment.

4) Your database is now created. You need to copy and save the database URL—highlighted in the following image—because you’ll need it later in your ESP32 code.

5) Set up Database Security Rules

Now, let’s set up the database rules. On the Realtime Database tab, select the Rules tab at the top. Then, click on Edit rules, copy the following rules and then click Publish.

// These rules grant access to a node matching the authenticated
// user's ID from the Firebase auth token
{
  "rules": {
    "UsersData": {
      "$uid": {
        ".read": "$uid === auth.uid",
        ".write": "$uid === auth.uid"
      }
    }
  }
}

These rules grant access to a node matching the authenticated user’s UID. This grants that each authenticated user can only access its own data. This means the user can only access the nodes that are under a node with its corresponding user UID. If there are other data published on the database, not under a node with the users’ UID, that user can’t access that data.

For example, imagine our user UID is RjO3taAzMMXBB2Xmir2LQ. With our security rules, it can read and write data to the database under the node UsersData/RjO3taAzMMXBB2Xmir2LQ.

You’ll better understand how this works when you start working with the ESP32.

6) ESP32 Datalogging (Firebase Realtime Database)

In this section, we’ll program the ESP32 board to do the following tasks:

1. Authenticate as a user with email and password ();
2. Get BME280 readings: temperature, humidity, and pressure;
3. Get epoch time (timestamp) from an NTP server;
4. Send sensor readings and timestamp to the realtime database as an authorized user.

Parts Required

For this project, you need the following parts*:

• board (read );
• or any other sensor you’re familiar with;
• ;       
• .

* you can also test the project with random values instead of sensor readings, or you can use any other sensor you’re familiar with.

You can use the preceding links or go directly to to find all the parts for your projects at the best price!

Schematic Diagram

In this tutorial, we’ll send BME280 sensor readings to the Firebase Realtime Database. So, you need to wire the BME280 sensor to your board.

We’re going to use I2C communication with the BME280 sensor module. For that, wire the sensor to the default ESP32 SCL (GPIO 22) and SDA (GPIO 21) pins, as shown in the following schematic diagram.

Not familiar with the BME280 with the ESP32? Read this tutorial: .

Installing Libraries

For this project, you need to install the following libraries:

Installing Libraries – VS Code

Follow the next instructions if you’re using VS Code with the PlatformIO extension.

Install the Firebase-ESP-Client Library

There is a library with lots of examples to use Firebase with the ESP32: the . This library is compatible with both the ESP32 and ESP8266 boards.

Click on the PIO Home icon and select the Libraries tab. Search for “Firebase ESP Client“. Select the Firebase Arduino Client Library for ESP8266 and ESP32.

Then, click Add to Project and select the project you’re working on.

Install the BME280 Library

In the Libraries tab, search for BME280. Select the Adafruit BME280 library.

Then, click Add to Project and select the project you’re working on.

Also, change the monitor speed to 115200 by adding the following line to the platformio.ini file of your project:

monitor_speed = 115200

Installation – Arduino IDE

Follow this section if you’re using Arduino IDE.

You need to install the following libraries:

Go to Sketch > Include Library > Manage Libraries, search for the libraries’ names and install the libraries.

For the Firebase Client library, select the Firebase Arduino Client Library for ESP8266 and ESP32.

Now, you’re all set to start programming the ESP32 board to interact with the database.

Datalogging—Firebase Realtime Database Code

Copy the following code to your Arduino IDE or to the main.cpp file if you’re using VS Code.

You need to insert your network credentials, project API key, database URL, and the authorized user email and password.

/*
  Rui Santos
  Complete project details at our blog: https://RandomNerdTutorials.com/esp32-data-logging-firebase-realtime-database/
  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files.
  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
*/

#include <Arduino.h>
#include <WiFi.h>
#include <Firebase_ESP_Client.h>
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>
#include "time.h"

// Provide the token generation process info.
#include "addons/TokenHelper.h"
// Provide the RTDB payload printing info and other helper functions.
#include "addons/RTDBHelper.h"

// Insert your network credentials
#define WIFI_SSID "REPLACE_WITH_YOUR_SSID"
#define WIFI_PASSWORD "REPLACE_WITH_YOUR_PASSWORD"

// Insert Firebase project API Key
#define API_KEY "REPLACE_WITH_YOUR_PROJECT_API_KEY"

// Insert Authorized Email and Corresponding Password
#define USER_EMAIL "REPLACE_WITH_THE_USER_EMAIL"
#define USER_PASSWORD "REPLACE_WITH_THE_USER_PASSWORD"

// Insert RTDB URLefine the RTDB URL
#define DATABASE_URL "REPLACE_WITH_YOUR_DATABASE_URL"

// Define Firebase objects
FirebaseData fbdo;
FirebaseAuth auth;
FirebaseConfig config;

// Variable to save USER UID
String uid;

// Database main path (to be updated in setup with the user UID)
String databasePath;
// Database child nodes
String tempPath = "/temperature";
String humPath = "/humidity";
String presPath = "/pressure";
String timePath = "/timestamp";

// Parent Node (to be updated in every loop)
String parentPath;

int timestamp;
FirebaseJson json;

const char* ntpServer = "pool.ntp.org";

// BME280 sensor
Adafruit_BME280 bme; // I2C
float temperature;
float humidity;
float pressure;

// Timer variables (send new readings every three minutes)
unsigned long sendDataPrevMillis = 0;
unsigned long timerDelay = 180000;

// Initialize BME280
void initBME(){
  if (!bme.begin(0x76)) {
    Serial.println("Could not find a valid BME280 sensor, check wiring!");
    while (1);
  }
}

// Initialize WiFi
void initWiFi() {
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to WiFi ..");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print('.');
    delay(1000);
  }
  Serial.println(WiFi.localIP());
  Serial.println();
}

// Function that gets current epoch time
unsigned long getTime() {
  time_t now;
  struct tm timeinfo;
  if (!getLocalTime(&timeinfo)) {
    //Serial.println("Failed to obtain time");
    return(0);
  }
  time(&now);
  return now;
}

void setup(){
  Serial.begin(115200);

  // Initialize BME280 sensor
  initBME();
  initWiFi();
  configTime(0, 0, ntpServer);

  // Assign the api key (required)
  config.api_key = API_KEY;

  // Assign the user sign in credentials
  auth.user.email = USER_EMAIL;
  auth.user.password = USER_PASSWORD;

  // Assign the RTDB URL (required)
  config.database_url = DATABASE_URL;

  Firebase.reconnectWiFi(true);
  fbdo.setResponseSize(4096);

  // Assign the callback function for the long running token generation task */
  config.token_status_callback = tokenStatusCallback; //see addons/TokenHelper.h

  // Assign the maximum retry of token generation
  config.max_token_generation_retry = 5;

  // Initialize the library with the Firebase authen and config
  Firebase.begin(&config, &auth);

  // Getting the user UID might take a few seconds
  Serial.println("Getting User UID");
  while ((auth.token.uid) == "") {
    Serial.print('.');
    delay(1000);
  }
  // Print user UID
  uid = auth.token.uid.c_str();
  Serial.print("User UID: ");
  Serial.println(uid);

  // Update database path
  databasePath = "/UsersData/" + uid + "/readings";
}

void loop(){

  // Send new readings to database
  if (Firebase.ready() && (millis() - sendDataPrevMillis > timerDelay || sendDataPrevMillis == 0)){
    sendDataPrevMillis = millis();

    //Get current timestamp
    timestamp = getTime();
    Serial.print ("time: ");
    Serial.println (timestamp);

    parentPath= databasePath + "/" + String(timestamp);

    json.set(tempPath.c_str(), String(bme.readTemperature()));
    json.set(humPath.c_str(), String(bme.readHumidity()));
    json.set(presPath.c_str(), String(bme.readPressure()/100.0F));
    json.set(timePath, String(timestamp));
    Serial.printf("Set json... %s/n", Firebase.RTDB.setJSON(&fbdo, parentPath.c_str(), &json) ? "ok" : fbdo.errorReason().c_str());
  }
}

How the Code Works

Continue reading to learn how the code works or skip to the .

Include Libraries

First, include the required libraries. The WiFi.h library to connect the ESP32 to the internet, the Firebase_ESP_Client.h  library to interface the boards with Firebase, the Wire, Adafruit_Sensor, and Adafruit_BME280 to interface with the BME280 sensor, and the time library to get the time.

#include <Arduino.h>
#include <WiFi.h>
#include <Firebase_ESP_Client.h>
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>
#include "time.h"

You also need to include the following for the Firebase library to work.

// Provide the token generation process info.
#include "addons/TokenHelper.h"
// Provide the RTDB payload printing info and other helper functions.
#include "addons/RTDBHelper.h"

Network Credentials

Include your network credentials in the following lines so that your boards can connect to the internet using your local network.

// Insert your network credentials
#define WIFI_SSID "REPLACE_WITH_YOUR_SSID"
#define WIFI_PASSWORD "REPLACE_WITH_YOUR_PASSWORD"

Firebase Project API Key, Firebase User, and Database URL

Insert your —the one you’ve gotten .

#define API_KEY "REPLACE_WITH_YOUR_PROJECT_API_KEY"

Insert the —these are the details of the user you’ve added .

// Insert Authorized Email and Corresponding Password
#define USER_EMAIL "REPLACE_WITH_THE_USER_EMAIL"
#define USER_PASSWORD "REPLACE_WITH_THE_USER_PASSWORD"

Insert your in the following line:

// Insert RTDB URLefine the RTDB URL
#define DATABASE_URL "REPLACE_WITH_YOUR_DATABASE_URL"

Firebase Objects and Other Variables

The following line defines a FirebaseData object.

FirebaseData fbdo;

The next line defines a FirebaseAuth object needed for authentication.

FirebaseAuth auth;

Finally, the following line defines a FirebaseConfig object required for configuration data.

FirebaseConfig config;

The uid variable will be used to save the user’s UID. We can get the user’s UID after the authentication.

String uid;

The databasePath variable saves the database main path, which will be updated later with the user UID.

String databasePath;

The following variables save the database child nodes for the temperature, humidity, pressure, and timestamp.

String tempPath = "/temperature";
String humPath = "/humidity";
String presPath = "/pressure";
String timePath = "/timestamp";

The parentPath is the parent node that will be updated in every loop with the current timestamp.

// Parent Node (to be updated in every loop)
String parentPath;

To better understand how we’ll organize our data, here’s a diagram.

It might seem redundant to save the timestamp twice (in the parent node and in the child node), however, having all the data at the same level of the hierarchy will make things simpler in the future, if we want to build a web app to display the data.

The timestamp variable will be used to save time (epoch time format).

int timestamp;

To learn more about getting epoch time with the ESP32 board, you can check the following tutorial:

We’ll send all the readings and corresponding timestamp to the realtime database at the same time by creating a JSON object that contains the values of those variables. The ESP Firebase Client library has its own JSON methods. We’ll use them to send data in JSON format to the database. We start by creating a variable of type FirebaseJson called json.

FirebaseJson json;

The ESP_Firebase_Client library provides some examples showing how to use FirebaseJson and how to send data in JSON format to the database:

We’ll request the time from pool.ntp.org, which is a cluster of time servers that anyone can use to request the time.

const char* ntpServer = "pool.ntp.org";

Then, create an Adafruit_BME280 object called bme. This automatically creates a sensor object on the ESP32 default I2C pins.

Adafruit_BME280 bme; // I2C

The following variables will hold the temperature, humidity, and pressure readings from the sensor.

float temperature;
float humidity;
float pressure;

Delay Time

The sendDataPrevMillis and timerDelay variables are used to check the delay time between each send. In this example, we’re setting the delay time to 3 minutes (18000 milliseconds). Once you test this project and check that everything is working as expected, we recommend increasing the delay.

// Timer variables (send new readings every three minutes)
unsigned long sendDataPrevMillis = 0;
unsigned long timerDelay = 180000;

initBME()

The initBME() function initializes the BME280 library using the bme object created previously. Then, you should call this library in the setup().

void initBME(){
  if (!bme.begin(0x76)) {
    Serial.println("Could not find a valid BME280 sensor, check wiring!");
    while (1);
  }
}

initWiFi()

The initWiFi() function connects your ESP to the internet using the network credentials provided. You must call this function later in the setup() to initialize WiFi.

// Initialize WiFi
void initWiFi() {
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to WiFi ..");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print('.');
    delay(1000);
  }
  Serial.println(WiFi.localIP());
  Serial.println();
}

getTime()

The getTime() function returns the current epoch time.

// Function that gets current epoch time
unsigned long getTime() {
  time_t now;
  struct tm timeinfo;
  if (!getLocalTime(&timeinfo)) {
    //Serial.println("Failed to obtain time");
    return(0);
  }
  time(&now);
  return now;
}

setup()

In setup(), initialize the Serial Monitor for debugging purposes at a baud rate of 115200.

Serial.begin(115200);

Call the initBME() function to initialize the BME280 sensor.

initBME();

Call the initWiFi() function to initialize WiFi.

initWiFi();

Configure the time:

configTime(0, 0, ntpServer);

Assign the API key to the Firebase configuration.

config.api_key = API_KEY;

The following lines assign the email and password to the Firebase authentication object.

auth.user.email = USER_EMAIL;
auth.user.password = USER_PASSWORD;

Assign the database URL to the Firebase configuration object.

config.database_url = DATABASE_URL;

Add the following to the configuration object.

// Assign the callback function for the long running token generation task
config.token_status_callback = tokenStatusCallback; //see addons/TokenHelper.h

// Assign the maximum retry of token generation
config.max_token_generation_retry = 5;

Initialize the Firebase library (authenticate) with the configuration and authentication settings we defined earlier.

// Initialize the library with the Firebase authen and config
Firebase.begin(&config, &auth);

After initializing the library, we can get the user UID by calling auth.token.uid. Getting the user’s UID might take some time, so we add a while loop that waits until we get it.

// Getting the user UID might take a few seconds
Serial.println("Getting User UID");
while ((auth.token.uid) == "") {
  Serial.print('.');
  delay(1000);
}

Finally, we save the user’s UID in the uid variable and print it in the Serial Monitor.

uid = auth.token.uid.c_str();
Serial.print("User UID: ");
Serial.print(uid);

After getting the user UID, we can update the database path to include the user UID.

// Update database path
databasePath = "/UsersData/" + uid + "/readings";

loop()

In the loop(), check if it is time to send new readings:

if (Firebase.ready() && (millis() - sendDataPrevMillis > timerDelay || sendDataPrevMillis == 0)){
  sendDataPrevMillis = millis();

If it is, get the current time and save it in the timestamp variable.

//Get current timestamp
timestamp = getTime();
Serial.print ("time: ");
Serial.println (timestamp);

Update the parentPath variable to include the timestamp.

parentPath= databasePath + "/" + String(timestamp);

Then, add data to the json object by using the set() method and passing as first argument the child node destination (key) and as second argument the value:

json.set(tempPath.c_str(), String(bme.readTemperature()));
json.set(humPath.c_str(), String(bme.readHumidity()));
json.set(presPath.c_str(), String(bme.readPressure()/100.0F));
json.set(timePath, String(timestamp));

Finally, call Firebase.RTDB.setJSON(&fbdo, parentPath.c_str(), &json) to append the data to the parent path. We can call that instruction inside a Serial.printf() command to print the results in the Serial Monitor at the same time the command runs.

Serial.printf("Set json... %s/n", Firebase.RTDB.setJSON(&fbdo, parentPath.c_str(), &json) ? "ok" : fbdo.errorReason().c_str());

Demonstration

Upload the previous code to your ESP32 board. Don’t forget to insert your network credentials, project API key, database URL, user email, and the corresponding password.

After uploading the code, press the board RST button so that it starts running the code. It should authenticate to Firebase, get the user UID, and immediately send new readings to the database.

Open the Serial Monitor at a baud rate of 115200 and check that everything is working as expected.

Aditionally, go to the Realtime Database on your Firebase project interface and check that new readings are saved. Notice that it saves the data under a node with the own user UID—this is a way to restrict access to the database.

Wait some time until you get some readings on the database. Expand the nodes to check the data.

Wrapping Up

In this tutorial, you learned how to log your sensor readings with timestamps to the Firebase Realtime Database using the ESP32. This was just a simple example for you to understand how it works.

You can use other methods provided by the ESP_Firebase_Client library to log your data, and you can organize your database in different ways. We organized the database in a way that is convenient for another project that we’ll publish soon.

In PART 2, we’ll create a Firebase Web App to display all saved data in a table and the latest readings on charts.

Part 2:

We hope you’ve found this tutorial useful.

If you like Firebase projects, please take a look at our new eBook. We’re sure you’ll like it:

Learn more about the ESP32 with our resources:

Thanks for reading.