Cost-Effective Solution for Resonance-Based Capacitive Sensors Readout

A simple and cost-effective resonance-based method for capacitance measurement is presented. The proposed method utilizes voltage measurement using the internal analog-to-digital converter (ADC) of a microcontroller (MCU) and detects resonance by estimating the frequency at which the measured voltage reaches its maximum value. The proposed circuit topology includes an MCU (ATMega4809), a direct digital synthesizer (AD9850), and a low-cost peak detector built with an operational amplifier (ADA4891) and a diode (1N4148). Simulations and experimental validation with six capacitors ranging from 1 nF to 10 nF showed that the proposed method is capable of measuring capacitance across a dynamic range spanning more than one decade, with an average measurement error of only 1.34%. An exponential fit using a single-phase decay equation produced an R2 value of 0.9968, indicating strong agreement between the measured resonant frequency and estimated capacitance. Compared to the existing solutions, the main advantages of the proposed system are its low complexity and cost, as it eliminates the need for high-speed, high-resolution ADCs. Moreover, the automated, MCU-based operation is particularly advantageous for portable and handheld readout electronics, applicable in various practical scenarios, such as object detection, proximity sensing, and electric capacitance tomography.