Gesture sensing is an increasingly practical way to interact with devices, particularly as wearables become more common. Your smartwatch may already respond to basic gestures like lifting your arm to check the time, or shaking it to clear a notification. But those usually work with an IMU (inertial measurement unit) that uses a non-trivial amount of electricity and requires a relatively significant amount of processing power. This new gesture sensing system is completely self-powered, and only requires photodiodes to work.
Photodiodes are extremely common and very inexpensive discrete components that are generally used as light sensors. They’re used in all kinds of devices, including remote control IR receivers and disc drives. Unlike most electronic components which consume power, photodiodes actually generate a tiny amount of electricity from the light they’re detecting, similar to small solar panels. This gesture sensor, created by researchers from the Dartmouth College Department of Computer Science, utilizes the energy-harvesting properties of photodiodes to power itself.
The gesture sensor is made up of multiple photodiodes that are laid out in either a line or rectangle pattern, which could easily be integrated into smartwatches and other wearables. When the user moves their finger across the photodiode array, the system detects a corresponding change in light levels and register a gesture. The user can move their finger in a variety of patterns and speeds to complete a number of different gestures. And, because the photodiodes are harvesting energy from the ambient light the whole time, the system doesn’t require any additional power source.