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To try Bluetooth Low Energy (BLE) with ESP-IDF, build Espressif’s NimBLE_GATT_Server example, flash it to a compatible ESP32-series development board, then use a phone to inspect its services, switch the board’s LED, and read or subscribe to sample heart-rate data. The heart-rate value is generated demonstration data—not a reading from a sensor.
What you will build
The example turns the development board into a BLE peripheral. A phone running nRF Connect for Mobile acts as the central and connects to the board. You can explore the board’s GATT services, write a characteristic to control the LED, and read or subscribe to the example’s heart-rate measurement characteristic.
This is a useful first project because it demonstrates the main BLE workflow without requiring a separate sensor: advertise, connect, discover data services, then exchange data through characteristics. Follow Espressif’s BLE introduction and getting-started guide for the example-specific walkthrough.
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Understand the BLE pieces you will use
Application, host, and controller
Espressif describes BLE software as three layers: application, host, and controller. Your application calls the host’s APIs. The host implements protocols such as GAP, GATT/ATT, SMP, and L2CAP, and communicates with the controller through HCI. The controller handles lower-level radio and link functions, including the PHY and Link Layer. Depending on the hardware design, host and controller functions can be integrated on one chip or separated.
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- Flexible Power-Saving Modes: ESP32 power-management features support dynamic clock scaling and low-power operating modes, helping developers reduce energy use in compatible sensing, monitoring and connected-device applications, suitable for battery-powered Internet of Things (IoT) devices.
- USB-C Programming with CP2102: Connect through USB-C for power, sketch uploads and serial monitoring, while GPIO, UART, SPI and I2C interfaces support sensors, displays, motor drivers and other modules (USB-C cable not included)
- Over-the-Air Update Support: Configure OTA functionality through a compatible ESP-32 software framework to update deployed firmware over Wi-Fi without reconnecting the board by USB for every revision
GAP: discovery and connection
GAP defines how devices are discovered and connected, along with the roles they take. An advertiser broadcasts advertising data; a scanner listens for it. An initiator can request a connection to an advertiser that accepts connections. Once connected, the advertiser is the peripheral and the initiator is the central. BLE also supports connectionless broadcast and observer roles, but this tutorial’s phone-to-board exercise uses a connection.
GATT and ATT: services and data
ATT defines attributes and how a client or server accesses them. An attribute has a handle, a type, a value, and permissions. Types are identified by UUIDs: common Bluetooth SIG-assigned identifiers are 16-bit, while vendor-defined identifiers are commonly 128-bit.
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GATT builds on ATT and organizes data into services and characteristics. A GATT server stores and manages characteristics; a GATT client discovers and accesses them. In this example, the board is the server and the phone is the client. A client can read a characteristic, write to it, or subscribe to updates when the characteristic supports notifications or indications.
Choose a Bluetooth host stack
ESP-IDF documents two host stacks. For a BLE-only first project, NimBLE is a natural fit; choose Bluedroid when the project also needs Classic Bluetooth. Confirm that your target chip and the example configuration support the stack you intend to use.
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| Stack | Bluetooth scope | Footprint note | When it fits |
|---|---|---|---|
| ESP-NimBLE | BLE only | Espressif says it requires less heap and flash than Bluedroid; the cited overview does not give a numerical footprint. | A BLE-focused project such as this tutorial. |
| ESP-Bluedroid | Classic Bluetooth and BLE | The cited overview does not provide a comparative numerical footprint. | A project that needs Classic Bluetooth as well as BLE. |
See Espressif’s Bluetooth overview and chip support information and the Bluetooth API index for current stack documentation and examples. Bluetooth controller, Bluedroid, and NimBLE support differs among ESP32-series chips, so check the matrix for your exact chip and verify the example’s configuration. ESP-IDF’s overview specifically describes ESP32 as supporting Dual-Mode Bluetooth 4.2 and being certified for Dual-Mode Bluetooth 4.2 and Bluetooth LE 5.0; those statements apply to ESP32, not automatically to every ESP32-series chip.
What you need
- An ESP32-series development board whose chip is supported by the example. Espressif does not prescribe a particular board model.
- An ESP-IDF development environment for the release you plan to use.
- A phone with nRF Connect for Mobile installed.
- A USB connection suitable for your board, for flashing and viewing serial output.
The commands below use the example path shown in Espressif’s guide. Replace <ESP-IDF Path> with your ESP-IDF installation path and <chip-name> with the target name for your board.
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Build and flash the NimBLE GATT server
- Open the example directory: in a terminal with the ESP-IDF environment available, change to
<ESP-IDF Path>/examples/bluetooth/ble_get_started/nimble/NimBLE_GATT_Server. - Set the target: run
idf.py set-target <chip-name>, using the target supported by your board. - Connect and flash: connect the board to the computer and run
idf.py flash monitor. The command builds and flashes the application, then opens its serial monitor.
Because ESP-IDF documentation and supported-chip configurations can change between releases, use the instructions and configuration for the ESP-IDF version and chip target actually selected.
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Connect from your phone and inspect the services
- Open nRF Connect for Mobile and start a scan.
- Find the device named
NimBLE_GATTand connect to it. - Inspect its discovered services. The walkthrough identifies GAP and GATT as foundational services, along with Heart Rate Service and Automation IO Service.
The Heart Rate Service UUID is 0x180D, and the Heart Rate Measurement characteristic UUID is 0x2A37. The LED characteristic uses a vendor-specific 128-bit UUID, so it will not have the same standardized identifier.
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Control the LED with a characteristic write
- In the connected device’s service list, open Automation IO.
- Open the LED characteristic and choose the write action.
- Select the ON or OFF value offered by the example, then send the write.
- Check the board’s LED for the change. If the board has no user LED, use the corresponding indication in the serial log instead.
This action illustrates a client writing a value to a server characteristic: the phone sends the selected value and the board’s example handles it.
Read or subscribe to the heart-rate example
Open the Heart Rate Measurement characteristic and either read its current value or enable updates by subscribing. Espressif’s example generates values fluctuating between 60 and 80 and updates them about once per second. These values are demonstration data, not a sensor measurement or a reliable health reading.
The Client Characteristic Configuration Descriptor (CCCD), UUID 0x2902, records whether notifications or indications are enabled. Subscribing in the phone app configures the client to receive the supported updates; it does not turn the generated value into a real sensor reading.
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If the example does not behave as expected
- The device does not appear during scanning: confirm that flashing completed, the board is running the example, and the phone is scanning nearby. Check serial output in the monitor for startup or configuration errors.
- The build or target configuration fails: verify that
<chip-name>matches the board’s chip and that the selected ESP-IDF release supports the example and stack for that target. - The LED does not visibly change: some boards have no user LED. Check the serial log for the example’s corresponding indication.
- The heart-rate value appears implausible: it is intentionally generated sample data, not a physiological reading.
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