A Flexible Raspberry Pi-Based Data Logger Platform for Modbus Sensors with Ansible Deployment

Abstract: This article presents LibrePiLogger, an open-source data logging platform based on the Raspberry Pi for environmental monitoring using Modbus sensors over RS-485. The system combines the AtmosPyre Python library for sensor communication with Ansible-based deployment automation, allowing researchers to deploy sensor networks by editing a single YAML inventory file. Two hardware configurations are described: a minimal setup using a Raspberry Pi Zero with an RS-485 HAT, and a maximal setup using a Raspberry Pi 4 with a USB-to-RS-485 converter. Currently implemented sensors include the Vaisala GMP252 for CO$_2$ and the RadonTech AlphaTRACER for $^{222}$Rn, with new sensors requiring approximately 100 lines of Python following a provided driver template. Data is logged to timestamped CSV files with JSON metadata. The system has been deployed for continuous CO$_2$ and $^{222}$Rn monitoring in a karst environment since spring 2025 and remains in active operation, demonstrating reliable long-term performance. All hardware designs, software, and deployment scripts are released under the GNU General Public License v3.0. Total hardware costs range from 54 to 63EUR (excluding housing), depending on the configuration.