BTHome Temperature Sensor

Overview

This application implements a Bluetooth Low Energy (BLE) temperature sensor using the BTHome format for data advertisement. BTHome is an energy-efficient format for transmitting sensor data over Bluetooth LE, compatible with popular home automation platforms like Home Assistant.

The application supports three different temperature sensors:

• Texas Instruments TMP112 - I2C digital temperature sensor (default)
• Maxim DS18B20 - 1-Wire digital temperature sensor
• Bosch BME680 - I2C environmental sensor (temperature + humidity)

Key features:

• Advertises temperature data every ~1 second using BTHome format
• Low power consumption suitable for battery-powered applications
• Supports both nRF52840 DK and nRF54L15 DK development boards
• Configurable sensor selection through Kconfig

Prerequisites

Hardware Requirements

• Nordic nRF52840 DK or nRF54L15 DK development board
• One of the supported temperature sensors:
  • TMP112 (I2C address 0x48)
  • DS18B20 (1-Wire)
  • BME680 (I2C address 0x76)
• Breadboard and jumper wires for sensor connections
• BTHome compatible listener (e.g., Home Assistant with BTHome integration)

Software Requirements

• nRF Connect SDK v2.4.0 or later
• West build tool
• nRF Connect for Desktop (for board configuration and flashing)

Sensor Connections

TMP112 (I2C)

Connect to nRF52840 DK:

• VCC → 3.3V
• GND → GND
• SDA → P0.26 (Arduino A4)
• SCL → P0.27 (Arduino A5)

DS18B20 (1-Wire)

Connect to nRF52840 DK:

• VCC → 3.3V
• GND → GND
• DATA → P1.02 (Arduino D1) with 4.7kΩ pull-up resistor to 3.3V

BME680 (I2C)

Connect to nRF52840 DK:

• VCC → 3.3V
• GND → GND
• SDA → P0.26 (Arduino A4)
• SCL → P0.27 (Arduino A5)

Building

Clone this repository under the samples folder in your nRF Connect SDK installation.

For nRF52840 DK

TMP112 sensor (default):

west build -b nrf52840dk/nrf52840 -- -DCONFIG_SENSOR_TMP112=y

DS18B20 sensor:

west build -b nrf52840dk/nrf52840 -- -DCONFIG_SENSOR_DS18B20=y

BME680 sensor (temperature + humidity):

west build -b nrf52840dk/nrf52840 -- -DCONFIG_SENSOR_BME680=y

For nRF54L15 DK

TMP112 sensor (default):

west build -b nrf54l15dk/nrf54l15/cpuapp -- -DCONFIG_SENSOR_TMP112=y

DS18B20 sensor:

west build -b nrf54l15dk/nrf54l15/cpuapp -- -DCONFIG_SENSOR_DS18B20=y

BME680 sensor (temperature + humidity):

west build -b nrf54l15dk/nrf54l15/cpuapp -- -DCONFIG_SENSOR_BME680=y

Flashing

After building, flash the application using west:

west flash

Or use nRF Connect Programmer from nRF Connect for Desktop.

Special Note for nRF54L15 DK

Before flashing firmware to the nRF54L15 DK:

1. Use the Board Configurator
2. Disable VCOM0
3. Set VDD to 3.3V
4. Apply the configuration before flashing

Usage

After flashing and powering on the device:

1. The device will start advertising as "BTHome sensor"
2. Temperature data is broadcast every ~1 second using BTHome format
3. For BME680, both temperature and humidity data are advertised

Console Output

You can monitor the device operation via RTT or UART:

Starting BTHome temp sensor
Bluetooth initialized
Sensor initialized
Temperature: 23.5°C
[BME680 only] Humidity: 45.2%

Viewing Sensor Data

Home Assistant

1. Ensure the BTHome integration is installed and configured
2. The sensor should be auto-discovered as "BTHome sensor"
3. Temperature (and humidity for BME680) will appear as sensor entities
4. Data updates approximately every second

Other BTHome Listeners

Any application supporting BTHome format can receive the sensor data. The device advertises:

• Service UUID: 0xFCD2 (BTHome)
• Data format: BTHome v2 (unencrypted)
• Temperature: 0.01°C resolution
• Humidity: 0.01% resolution (BME680 only)

Troubleshooting

Device Not Advertising

• Check that the sensor is properly connected and powered
• Verify the correct sensor configuration is selected
• Monitor console output for initialization errors
• Ensure the device is not already connected to another BLE central

Sensor Reading Issues

• TMP112/BME680: Check I2C connections and pull-up resistors
• DS18B20: Verify 1-Wire connection and 4.7kΩ pull-up resistor
• Check sensor power supply (3.3V)
• Verify sensor address matches overlay configuration

Home Assistant Not Discovering

• Ensure BTHome integration is installed
• Check Bluetooth adapter range and interference
• Restart Home Assistant if discovery is delayed
• Check HA logs for BTHome-related errors

Build Errors

• Ensure nRF Connect SDK is properly installed
• Check that you're in the correct directory
• Verify the target board is supported
• Clean build directory: west build -t clean

Project Structure

├── boards/                    # Board-specific overlays
│   ├── nrf52840dk_nrf52840.overlay
│   └── nrf54l15dk_nrf54l15_cpuapp.overlay
├── include/
│   └── sensor.h              # Sensor interface header
├── src/
│   ├── main.c                # Main application and BLE advertising
│   └── sensor.c              # Sensor initialization and reading
├── CMakeLists.txt           # Build configuration
├── Kconfig                  # Configuration options
├── prj.conf                 # Project configuration
└── README.rst              # This file

For more information about BTHome format, visit https://bthome.io