Improving the performance of Bio-Impedance Spectroscopy via Dynamic Direct Sampling : design and test of a low-Cost Microcontroller based device

A portable impedance spectroscopy (IS) device has been developed based on the STM32F407 commercial microcontroller. The microcontroller has been programmed to perform dynamic sampling in response to the sinusoidal input signal, effectively addressing oversampling issues for multi-frequency analysis and reducing acquisition time through an internal clock optimization algorithm. The resulting architecture further reduces overall size, enhancing device portability. Validation tests were conducted using electrical circuits designed to mimic the characteristics of biological samples. The experimental results were compared with theoretical transfer functions derived from simulated impedances in the 10-200 kHz range under sinusoidal current excitation to preserve bioimpedance linearity. In the worst-case scenario, the device demonstrated a maximum mean magnitude error of 3.48% and a maximum mean phase error of 1.71 degrees when compared to the ideal transfer function of the equivalent impedance. These results highlight the performances achieved by the low-cost, portable IS device.