A Comparison-Based Interface Circuit for Detection of Motion Direction of Humans Using Capacitive Sensor

This article presents a novel, noncontact capacitive principle-based measurement system to detect the proximity and motion direction of humans while disregarding other objects. The proposed system uses a three-electrode coplanar capacitive sensor architecture that can be easily mounted on the side jamb of the door. A novel comparison-based interface circuit is incorporated into the system, which creates a distinct pattern for different directions of human motion. The working principle of the sensing system is based on the shielding effect, where the sensor capacitances decrease when humans pass through the doorway. The interface circuit is designed to accommodate both symmetrical and asymmetrical capacitive sensor configurations. The overall power consumption of the experimental prototype developed is approximately 27 mW and costs around U.S. ${\$}$ 15. The designed interface circuit has the ability to tolerate a sensor leakage resistance as low as 0.2 $\text{k}\Omega $ with an error of 0.262% and offers a power line interference (PLI) attenuation of −90.42 dB. The system’s versatility and potential are demonstrated through extensive testing, and the results are presented. Furthermore, a negative capacitance shunt-based feedback scheme in the interface circuit is proposed, which not only enhances the detection range to 70 cm but also alleviates the performance requirements of integrated circuits (ICs) used in the prototype. Consequently, the system’s overall cost is reduced to U.S. ${\$}$ 11. In addition, the power dissipation can be further minimized by employing compact, low-power-consuming ICs.