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Existing smartwatches offer convenient health monitoring and interfaces with mobile devices. However, the interactivity between a user and a smartwatch suffers from the limited size of the screen and buttons. To improve the usability of smartwatches, novel human-computer interaction methods are introduced into the watchband. To this end, we present a modular lightweight watchband consisting of various capacitive sensing modules—TouchBand. It is made with a flexible printed circuit board (PCB) supporting the bottom electrodes, silver-coated conductive fabric as the top electrodes, and Eco-Flex as the dielectric to electrically separate the PCB and fabric. The watchband incorporates three control modules—(i) two shear-sensitive pressure sensing buttons, (ii) two capacitive sliders, and (iii) one proximity sensing array for hand gesture recognition. Shear forces are captured by analyzing the asymmetric changes in multiple mutual-capacitance readings produced by a shear motion between the top and bottom layers, where overlapped electrodes reside. Sliders pick up changes in proximity as fingers are moved across the sensor surfaces. Hand gestures could be recognized by monitoring the capacitance-based proximity readings between the watchband electrodes and the user’s skin. Eyes-free input to the watch becomes feasible by providing a shear/sliding touch input to the watchband as well as performing a free-hand gesture on the wearing hand. With a flexible printed circuit (FPC) connection to the compact custom electronics, all modules of the watchband were sampled at 50 Hz while consuming 30 mW of power. Meanwhile, the measurement data was wirelessly transmitted through Bluetooth Low-Energy 5.0 (BLE) to a nearby mobile device for real-time data analysis and visualization.
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