Introduction

Helium Meteo is a small battery-powered device for measuring temperature, humidity and atmospheric pressure. Data samples are transmitted via Helium LoRaWan.

Data is received from the Helium network by the provided simple implementation. A cheap ARM single-board computer is usually sufficient to run it at home.

See below an overview of the software architecture. This project provides the components colored in red:

BOM

• Olimex BB-STM32WL-ANT.
• Olimex MOD-BME280.

Wiring is simple - connect ground, VCC and I2C from MOD-BME280 to the respective pins of BB-STM32WL. There is no need for pull-ups - MOD-BME280 already has them.

Getting Started

Before getting started, make sure you have a proper Zephyr development environment. You can follow the official Zephyr Getting Started Guide.

Initialization

The first step is to initialize the workspace folder where the helium_meteo and needed Zephyr modules will be cloned. You can do that by running:

# initialize workspace for the helium_meteo (main branch)
west init -m https://github.com/dinuxbg/helium_meteo --mr main helium_meteo_project
# update Zephyr modules
cd helium_meteo_project/helium_meteo
west update

Build & Run

The application can be built by running:

west build -d build -b olimex_lora_stm32wl_devkit@D -s helium_meteo/app  --pristine

Once you have built the application you can flash it by running:

west flash

Serial terminal

Hook a serial UART to LPUSART1. You would get access to a shell running on the device, where you can setup the Helium/LoRaWan keys and tweak other settings.

screen /dev/ttyACM0 9600

Type help to get a list of supported commands.

Configuring Helium parameters

In order to connect to the Helium network, you must first set the keys. Reboot the board after that for the settings to take effect.

lorawan dev_eui AABBCCDDEEFF0011
lorawan app_eui 0000000000000000
lorawan app_key 123456789ABCDEFFEDCBA98765432101
lorawan auto_join true
kernel reboot cold

Note: With the new ChirpStack, app_eui should be set to 0. Only the now-deprecated Helium Console requires a valid app_eui.

Acknowledgements

This project is heavily based on https://github.com/retfie/helium_mapper .

TODO

• Design a custom PCB.
• Create a custom board definition for Zephyr instead of inheriting stm32wl_devkit.
• Add more documentation (e.g. how to setup Helium/LoRaWan keys).
• Add battery voltage measurement to the Lora packet.
• Add driver for AHT20 sensor, so that firmware can run directly on LoRa-STM32WL-DevKit, no custom wiring required.