The ecological impact of today’s battery-powered Internet of Things (IoT) is troubling. Technology advancements that reduce the reliance on batteries could blunt the environmental impact of the projected billions of IoT devices. With the emergence of low-cost, small, and high-performance microcontrollers, along with more efficient micro-energy harvesting devices that can harness the power of sunlight, motion, and heat a new revolution in computing has come. That is, IoT devices are increasingly leaving their batteries behind and are relying only on ambient power from sunlight, motion, thermal gradients, and other modalities to power their operation. Unfortunately, harvested energy can fluctuate greatly and is hard to predict, leading to intermittent operation. Intermittently-powered devices form a new class of low-power devices that can guarantee correct and forward-progressing computation despite these frequent power interrupts. Despite the inconvenience of intermittent operation, the benefit of using intermittently-powered devices instead of ‘classical’ battery-based ones is threefold. The removal of batteries creates a more environmentally-friendly device, harvesting energy from ambient sources is sustainable and removing the battery can potentially lead towards perpetual operation—as long as there is an ambient energy source, battery-free devices will continue operating. Challenges of battery-free devices however, still include basic features that are foundational to IoT devices. Interaction with battery-free devices has so far remained largely unexplored although reactive and screen-oriented systems are a significant part of today’s and future Internet of Things. Common tools used during development, such as debuggers and testing frameworks, are practically non-existent for intermittent devices. Even basic concepts such as keeping track of time need to be carefully considered on intermittently-powered devices. Finally, wireless networking of intermittently-powered devices is severely limited to only backscatter or one directional communication. This dissertation addresses the challenges mentioned above by developing and deploying mechanisms that enable connected and fully interactive applications on battery-free devices. These mechanisms alleviate key challenges that hinder actual adoption and infrastructure-less deployment of these battery-free devices.@en

Debugging and testing battery-free intermittently-powered systems is notoriously difficult. This is not only due to the additional complexity of maintaining state through power failures but also due to the lack of proper tools to test and debug these systems. As a solution, we present DIPS: a fully-featured hardware debugger for battery-free intermittently-powered systems capable of automatically verifying memory and peripheral state between power failures. Our solution seamlessly integrates an emulator allowing for emulation of any power scenario to the device under test. This allows our debugger to pause emulation and program execution when debugging or when state restoration issues are detected. Our new system is built around GNU Debugger (GDB): a widely-used debugging tool. Therefore, DIPS allows for a debugging process identical to state-of-the-art debuggers for continuously-powered devices. User studies found that our debugger is easy and intuitive to use. It allows embedded system developers to find bugs quicker in code written for battery-free devices. With our debugger we found unseen errors in state-of-the-art software frameworks for intermittently-powered systems.@en

We present an architecture for intermittently-powered wireless communication systems that does not require any changes to the official protocol specification. Our core idea is to save the intermediate state of the wireless protocol to non-volatile memory within each connection interval. The protocol state is then deterministically restored at a predefined (harvested energy-dependent) time, which follows the connection interval. As a case study for our architecture, we introduce FreeBie: a battery-free intermittently-powered Bluetooth Low Energy (BLE) mote. To the best of our knowledge FreeBie is the first battery-free active wireless system that sustains bi-directional communication on intermittent harvested energy. The strength of our architecture is articulated by FreeBie consuming at least 9.5 times less power during device inactivity periods than a state-of-the-art BLE device.

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Any future mobile electronic device with which a user interacts (smartphone, hand-held game console) should not pollute our planet. Consequently, designers need to rethink how to build mobile devices with fewer components that negatively impact the environment (by replacing batteries with energy harvesting sources) while not compromising the user experience quality. This article addresses the challenges of battery-free mobile interaction and presents the first battery-free, personal mobile gaming device powered by energy harvested from gamer actions and sunlight. Our design implements a power failure resilient Nintendo Game Boy emulator that can run off-the-shelf classic Game Boy games like Tetris or Super Mario Land. Beyond a fun toy, our design represents the first battery-free system design for continuous user attention despite frequent power failures caused by intermittent energy harvesting.@en

Energy-harvesting devices have enabled Internet of Things applications that were impossible before. One core challenge of batteryless sensors that operate intermittently is reliable timekeeping. State-of-the-art low-power real-time clocks suffer from long start-up times (order of seconds) and have low timekeeping granularity (tens of milliseconds at best), often not matching timing requirements of devices that experience numerous power outages per second. Our key insight is that time can be inferred by measuring alternative physical phenomena, like the discharge of a simple RC circuit, and that timekeeping energy cost and accuracy can be modulated depending on the run-time requirements. We achieve these goals with a multi-tier timekeeping architecture, named Cascaded Hierarchical Remanence Timekeeper (CHRT), featuring an array of different RC circuits to be used for dynamic timekeeping requirements. The CHRT and its accompanying software interface are embedded into a fresh batteryless wireless sensing platform, called Botoks, capable of tracking time across power failures. Low start-up time (max 5 ms), high resolution (up to 1 ms) and run-time reconfigurability are the key features of our timekeeping platform. We developed two time-sensitive batteryless applications to demonstrate the approach: a bicycle analytics tool-where the CHRT is used to track time between revolutions of a bicycle wheel, and wireless communication-where the CHRT enables radio synchronization between two intermittently-powered sensors.

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We present ENGAGE, the first battery-free, personal mobile gaming device powered by energy harvested from the gamer actions and sunlight. Our design implements a power failure resilient Nintendo Game Boy emulator that can run off-the-shelf classic Game Boy games like Tetris or Super Mario Land. This emulator is capable of intermittent operation by tracking memory usage, avoiding the need for always checkpointing all volatile memory, and decouples the game loop from user interface mechanics allowing for restoration after power failure. We build custom hardware that harvests energy from gamer button presses and sunlight, and leverages a mixed volatility memory architecture for efficient intermittent emulation of game binaries. Beyond a fun toy, our design represents the first battery-free system design for continuous user attention despite frequent power failures caused by intermittent energy harvesting. We tackle key challenges in intermittent computing for interaction including seamless displays and dynamic incentive-based gameplay for energy harvesting. This work provides a reference implementation and framework for a future of battery-free mobile gaming in a more sustainable Internet of Things.

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