To send data from an Arduino project to Firebase, the board must be able to make HTTPS requests. A Wi-Fi-capable ESP32 or ESP8266 is a practical starting point: write a JSON value to Firebase Realtime Database, then read it back with a separate request. A one-time read is not a live listener, and access depends on correctly configured Firebase Authentication and Security Rules.
What you need before connecting
A board with network access
A classic Arduino Uno does not include Wi-Fi. Use a compatible ESP32 or ESP8266 development board, or add a network module that supports HTTPS and is compatible with your chosen client library. Confirm compatibility among the board, Arduino core, library, TLS setup, and available memory before building the sketch.
The current Mobizt FirebaseClient README lists ESP32 and ESP8266 support, along with installation options. Its supported-device list also includes 32-bit MCUs except Atmel AVR. Follow the README and examples for the library version you install; APIs can change.
A Firebase project and Realtime Database
Create a Firebase project and a Realtime Database, choose its location, and copy the database URL shown in the Firebase console. The URL hostname depends on the database location: Firebase documents DATABASE_NAME.firebaseio.com for us-central1, and DATABASE_NAME.REGION.firebasedatabase.app for other locations. Do not assume a hostname from an example; use your project’s actual URL.
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For REST requests, Firebase forms a database endpoint by appending .json to the database URL or the relevant path. For example, a request to /devices/deviceA/reading uses an endpoint ending in /devices/deviceA/reading.json. REST requests require HTTPS. See Firebase’s REST API setup documentation.
A current library and credentials
Install FirebaseClient using one of the methods in its README, such as Arduino IDE Library Manager, a manual ZIP installation, or PlatformIO. Use a matching library example rather than copying an older sketch without checking its API and authentication method.
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Set up access before writing data
Realtime Database Security Rules are enforced on Firebase’s servers. Firebase says default rules deny access; a request succeeds only when it is authenticated as required and permitted by the rules for the requested path and operation.
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For an application with users, use a suitable user-level credential, such as a Firebase ID token, and scope rules to the data each user should access. Firebase documents Firebase ID tokens and Google OAuth2 access tokens for REST authentication in its REST authentication guide. Avoid public read/write rules for deployed projects. Rules can use authentication information such as a user’s UID to restrict access; see Firebase’s guides to Realtime Database Security Rules and conditional rules.
Never place a privileged service-account key in a board sketch, client firmware, or public repository. Firebase warns that service-account credentials should not be exposed or deployed in a client app. A service account is for trusted server-side access, not a secret to embed in a device that users can inspect.
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Send a JSON value to Realtime Database
Decide first whether your project needs only the latest state or a growing history. A write to a fixed path replaces the value at that path; it does not automatically preserve earlier readings. For a latest sensor reading, a path such as /devices/deviceA/reading is straightforward. For a history, use a structure and write operation designed to add records rather than repeatedly overwrite one fixed location. Firebase documents REST write methods in Saving Data.
- Connect the board to Wi-Fi. Configure the network name and password using a method appropriate for your project, then confirm that the board has connected before attempting Firebase requests.
- Configure the Firebase client. Set the project’s actual Realtime Database URL and the appropriate authentication credentials using the installed library’s current examples. Do not substitute a service-account private key as a client credential.
- Choose the database path and JSON shape. For example, a JSON object might contain a numeric reading and a timestamp. Ensure the path and JSON match the rules you intend to enforce.
- Write to the path. Send the library’s supported write request over HTTPS to the selected Realtime Database location. Verify that the response indicates success; a successful request changes the value at the target path according to the write method used.
At the REST level, Firebase’s endpoint convention is to append .json to the database URL and target path. The precise client-library calls depend on the version and authentication flow you select, so use the matching FirebaseClient example rather than assuming that code for a deprecated library will compile unchanged.
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Read the value back
To retrieve the stored value, make a separate read request to the same path. Firebase REST uses GET for reads. A request to the matching .json endpoint returns the value currently stored there, subject to authentication and Security Rules. This is a one-time read: it tells the board what the database contains when that request is made, not whenever the value changes.
- Use the same database URL and path as the write, including the
.jsonREST suffix where applicable. - Issue a read request with the library’s supported API and valid credentials.
- Parse the returned JSON and handle the case where the path is absent or the returned value has a different shape than expected.
Choose how the board should receive updates
| Approach | What the board receives | Trade-off |
|---|---|---|
| One-time read | The value at the moment of the request. | Simple, but it does not detect later changes unless the board reads again. |
| Periodic polling | A fresh value each time the board repeats a read request. | Easy to reason about, but creates repeated requests and can notice a change only when the next read occurs. |
| REST event stream | Database change events over a continuing connection. | Requires Server-Sent Events handling, including the Accept: text/event-stream header and HTTP 307 redirects; support depends on the chosen client implementation. |
Firebase’s REST API reference documents Server-Sent Events for streaming and describes the required event-stream header, redirects, and authentication behavior. A stream is not equivalent to a single GET. Although the Firebase REST API supports streaming, the FirebaseClient README notes limitations around change-listening behavior. Verify that the specific library version and board support the listening mode your application needs before choosing it.
Troubleshoot failed reads and writes
- Network connection: confirm the board joined Wi-Fi and can make HTTPS connections.
- Database URL: copy the URL from the Firebase console and check that it matches the database’s region.
- TLS and HTTPS: the REST API requires HTTPS; confirm that the board’s networking setup supports it.
- Authentication: check that the token is valid, supplied in the expected way, and has the permissions the rules require.
- Path and JSON: confirm the database path, REST
.jsonsuffix, and JSON syntax or shape. - Security Rules: verify that rules permit the intended operation for the authenticated identity. Firebase’s REST API reference documents authentication and rule violations among possible errors.
- Streaming details: if using Server-Sent Events, handle the event-stream header and HTTP 307 redirects, and check that the library actually supports the required change-listening behavior.
Use Firebase’s Realtime Database REST API reference to check request methods, streaming behavior, and documented error responses.
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