A low-cost portable system for 3-Axis measurement of static and extremely low frequency magnetic fields

Magnetic fields play a crucial role in modern science and technology - yet precise and accessible tools for their measurement remain limited, especially for small laboratories, educators, or independent researchers. This paper introduces a novel, open-source magnetic field measurement system based on three-axis sensors for monitoring both direct and extremely low frequency magnetic fields. The device features a modular hardware design centered around a custom PCB, enabling flexible analog filtering, Bluetooth data transmission, and offline LCD visualization. By combining the MC858 and MPU9250 sensors with precise analog signal conditioning and a 12-bit ADC, the system ensures reliable detection of magnetic fields including the 50 Hz mains frequency and its harmonics. To verify the functionality of the device, experimental measurements were conducted inside a Faraday cage using a common hair dryer placed at distances of 1 cm and 3 cm from the sensors as a source of electromagnetic field. Frequency analysis confirmed reliable detection of the dominant 50 Hz component and its harmonics, as well as the system's ability to distinguish changes in field intensity based on distance and operating state of the source device.