Cricket: A Self-Powered Chirping Pixel

TL;DR

The paper tackles battery-free, wireless light sensing by harvesting energy from ambient illumination. It introduces cricket, a minimalist analog sensor that emits short RF chirps when energy suffices; the chirp carrier identifies the device, while the inter-chirp interval encodes light with a wide dynamic range, enabling untethered sensing and even simple video-like arrays. Key contributions include a working 24-cricket prototype with linear radiometric response over a $10$ to $170{,}000$ lux range, a cricket cube for centroid estimation with low angular error, and practical demonstrations in lighting control and battery-free eTransition sunglasses. The work demonstrates practical, scalable, battery-free sensing for solar tracking, energy-efficient lighting, and embedded sensing, with potential extensions to additional environmental parameters. These results point to compact, self-powered sensor networks capable of real-time, wireless illumination monitoring and control.

Abstract

We present a sensor that can measure light and wirelessly communicate the measurement, without the need for an external power source or a battery. Our sensor, called cricket, harvests energy from incident light. It is asleep for most of the time and transmits a short and strong radio frequency chirp when its harvested energy reaches a specific level. The carrier frequency of each cricket is fixed and reveals its identity, and the duration between consecutive chirps is a measure of the incident light level. We have characterized the radiometric response function, signal-to-noise ratio and dynamic range of cricket. We have experimentally verified that cricket can be miniaturized at the expense of increasing the duration between chirps. We show that a cube with a cricket on each of its sides can be used to estimate the centroid of any complex illumination, which has value in applications such as solar tracking. We also demonstrate the use of crickets for creating untethered sensor arrays that can produce video and control lighting for energy conservation. Finally, we modified cricket's circuit to develop battery-free electronic sunglasses that can instantly adapt to environmental illumination.

Figures (17)

• Figure 1: Cricket circuit. When the photovoltaic cell is exposed to light, the voltage across the capacitor $C_1$ begins to rise. At a certain voltage, the circuit comes alive and the oscillator generates a short and strong chirp. The time between consecutive chirps reveals the intensity of incident light.
• Figure 2: Cricket prototype. The photovoltaic cell, printed circuit board and RF antenna are stacked and packaged in a compact 3D-printed case.
• Figure 3: Cricket voltages. The waveforms of the voltage $V_c$ of the capacitor $C_1$ and the comparator output $V_o$, measured using an oscilloscope. The oscillator is connected to the antenna only after its output frequency has stabilized.
• Figure 4: Chirp detection. (a) Signal from a single cricket received by the software defined radio. (b) A time-expanded view of a single chirp. (c) The known carrier frequency $f_{id}$ of the cricket is used to detect chirps in frequency domain. Here, the power within a small window around $f_{id}$ is plotted as a function of time. The frequency $f_c$ of received chirps (chirps per second) is proportional to the incident light level.
• Figure 5: Performance characteristics of crickets. (a) Experimental setup used to evaluate the performance of crickets. The cricket is illuminated using a regulated halogen light source. A luxmeter is placed close to the cricket to obtain ground truth light levels. In these experiments, the software defined radio was placed roughly 12 ft from the cricket. (b) The radiometric response of a cricket was found to be linear. Also shown is a zoomed-in view of the response function for low light levels ($0-100 \ \unit{lux}$). Ideally, the response function should pass through the origin. It does not in our measurements because of a small error (roughly $7 \ \unit{lux}$) in the measurements produced by the luxmeter, which were used as ground truth. (c) The PSNR of a cricket for different light levels.