We introduce a low-cost, flexible switchbox that automates Electrical Resistivity Tomography (ERT) surveys using a standard 4-electrode resistivity meter. Addressing the prohibitive cost of commercial multi-electrode systems, this solution utilizes affordable Arduino microcontroller technology, relay modules, and open-source software (Python/Arduino). The switchbox acts as an interface, automatically connecting the meter’s terminals (C1, C2, P1, P2) to the correct field electrodes based on chosen sequences. It supports standard ERT arrays (Wenner, Dipole-Dipole, etc.) and allows users to implement custom configurations, enhancing research flexibility. Validated in both lab settings (negligible error) and field trials—including archaeological sites in Birmingham (UK) and Negrilesti (Romania), plus urban tree root detection—the system proved reliable. Costing only a couple hundred euros for components, it offers significant advantages: affordability, operational flexibility, portability, and suitability for time-lapse monitoring. This makes advanced ERT techniques accessible for budget-constrained research, education, humanitarian projects, and urban geophysics applications.