Using CAPSENSE in a Wearable Textile Chest Belt for Respiration Sensing and Interaction Possibility

Textile sensor integration in clothing creates new fields of application because of their imperceptability during human activity for gathering biometric data, especially in sports. [1]However, smart textiles pose new challenges for research and development. Textile capacitive sensors are used in numerous wearable garments and generally more robust than resistive sensors, [2] however, they are affected by external influences, e.g. temperature and moisture. [3] Within this work, we present the applicability and advantages of the CAPSENSE™ technology (CAPSENSE; Infineon) in an improved version of a wearable running stride and respiration sensor (SRS) (see Figure 1).[4]After experimenting with capacitive sensing solutions, e.g. capacitive voltage division and capacitive touchpins using an ESP32 chipset (Espressif Systems, China), it was decided to use a PSoC™ microcontroller unit (PSoC; Infineon) with integrated CAPSENSE function to measure the capacitance changes of the respiratory sensor. The PSoC enables parallel CAPSENSE input channels and thus the simultaneous determination of different measured values. Besides self-capacitance sensing, CAPSENSE additionally provides mutual-capacitance scanning between a Tx and Rx electrode for increased sensitivity and accuracy. In addition, an auto-calibration function is applied to counteract negative external influences, e.g. due to temperature and moisture. Therefore, we integrate a smart-textile sensor in parallel to the respiration smart-textile sensor as input touch button to manually trigger the auto-calibration function at self-selected times.Regarding first pilot tests, CAPSENSE improves the respiration signal quality compared to the initial SRS. The signal quality is evaluated in an upcoming study regarding the signal-to-noise ratio.In addition, the textile input touch button will be evaluated according to a proper functionality.The investigated technology and the resulting prototype integrated into a chest strap enables further research and studies. The improved SRS will be used to investigate if runner can be guided towards a locomotor respiratory coupling by sound instructions provided by a smartphone application.[5],[6] The number of textile interaction buttons on the SRS can be increased to allow on-body touch interaction, which has proven to be effective and user-friendly whilst performing sports. [7] As such, CAPSENSE could enable a phoneless interaction to be holistically integrated in the sports experience.