Experimental characterization of off-the-shelf LEDs as photodetectors for waking up microcontrollers

Ripoll-Vercellone, Edgar; Reverter, Ferran; Ferrandiz, Vicent; Gasulla, Manel

doi:10.1109/i2mtc.2019.8826967

Cited by 4 publications

(6 citation statements)

References 6 publications

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“…This is further demonstrated with the current-voltage curves shown in the inset of Figure 2 in terms of a larger photo-current generation for the PDs and lower short circuit current of the LED. This is in line with our expectations and explains why the bulk of the literature continues to use photodiodes, rather than LEDs as light detectors, which is in agreement with earlier discussions [ 24 , 43 ]. Figure 2 also presents the normalised response of the LED along with the emission spectra of the excitation LED, which overlaps strongly with the response range of the LEDs being used as detectors.…”

Section: Resultssupporting

confidence: 93%

Advances in Optical Based Turbidity Sensing Using LED Photometry (PEDD)

Fay

Nattestad

2021

Sensors

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Turbidity is one of the primary metrics to determine water quality in terms of health and environmental concerns, however analysis typically takes place in centralized facilities, with samples periodically collected and transported there. Large scale autonomous deployments (WSNs) are impeded by both initial and per measurement costs. In this study we employ a Paired Emitter-Detector Diode (PEDD) technique to quantitatively measure turbidity using analytical grade calibration standards. Our PEDD approach compares favorably against more conventional photodiode-LED arrangements in terms of spectral sensitivity, cost, power use, sensitivity, limit of detection, and physical arrangement as per the ISO 7027 turbidity sensing standard. The findings show that the PEDD technique was superior in all aforementioned aspects. It is therefore more ideal for low-cost, low-power, IoT deployed sensors. The significance of these findings can lead to environmental deployments that greatly lower the device and per-measurement costs.

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Section: Resultssupporting

confidence: 93%

Advances in Optical Based Turbidity Sensing Using LED Photometry (PEDD)

Fay

Nattestad

2021

Sensors

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“…As a proof-of-concept, a prototype of the circuit in Fig. 1 was designed with the following devices: 1) a low-cost flat-top red LED (150060RS75000, Wurth Electronics) that provides high enough values of ∆vD at indoor and outdoor conditions without requiring very high values of RD [12]; 2) a small-signal NMOS (RE1C002UN, RHOM) that offers low values of both CM and VT ; and 3) an STM32L072 MCU with an interruption pin (PA0) that is activated at the rising edge of vM. For illuminating the LED, we used, depending on the performed tests, either the flashlight of a Motorola Moto X Style (XT1572) smartphone placed at a distance of 1 cm or a high-power white LED that emulated it [12].…”

Section: Resultsmentioning

confidence: 99%

“…However, artificial and ambient interfering lights could also wake-up the MCU. To palliate this, a resistor (RD) is added in parallel with the LED [12]. In this way, vD is proportional to the generated LED current (iD), thus allowing a better discrimination between different light intensities.…”

Section: Wake-up Circuitmentioning

confidence: 99%

LED-Based Wake-Up Circuit for Microcontrollers

Ripoll-Vercellone¹,

Reverter

Gasulla

2020

IEEE Trans. Instrum. Meas.

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This paper proposes, analyzes, and tests a wake-up circuit for a microcontroller (MCU) that uses a LED, operating as a photodetector, illuminated by a smartphone flashlight. The wake-up circuit consists of a high-pass filter and a voltage level translator that interfaces the LED, with a suitable resistor in parallel, to the MCU. When illuminated by a switching flashlight, the LED generates a square voltage that is conveniently converted in logic levels at the output of the wake-up circuit. A firmware embedded into the MCU additionally checks that a predetermined sequence of logic pulses at a given rate is accomplished to activate the MCU. The paper includes a theoretical analysis and experimental results that validate the proposed circuit.

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“…• Publication IV. Conference proceeding III: "Experimental characterization of off-the-shelf LEDs as photodetectors for waking up microcontrollers" [201]. It is reproduced in Chapter 3, section 3.2.…”

Section: Publicationsmentioning

confidence: 99%

“…Publication IV tackles the LEDs current-voltage characterization problem. An initial characterization of twenty LEDs with a high-power white emitting LED (emulating the smartphone flashlight, as defined in [201]) was first carried out to choose the appropriate ones for the study. The same setup as in [201] was utilized.…”

Section: Data Availability Statementmentioning

confidence: 99%

Design and implementation of wireless nodes for the Internet of Things

Ripoll Vercellone

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The Internet of Things is a trending topic these days. However, energy is often the major job stopper for broad adoption of this technology, which have three tight constraints: extremely cost oriented, long service life and small size. As a consequence, developers must overcome many challenges related to the optimal management of the energy available to power a node. This management is not only limited to the power supply, but also comprises the smart energy consumption of the node. Three challenges are addressed in this work: the first associated with the node’s sensing system, the second, with the power consumption when the node is not operating, and the third, with the energy harvesting. The contributions of this thesis are presented as an articlebased dissertation of three journal publications and three conference articles, where each publication addresses one of the challenges. The first contribution is related to the node’s sensing system. Particularly, the electronic gas meters’ sensing system. A novel sensing system for gas meters has been developed. It is based on a dual magnetic sensing: a) low-cost, low-power primary sensing via reed switches connected to the microcontroller's (MCU) digital inputs, and b) secondary sensing using Hall-effect sensors coupled to the MCU's analogue inputs. Furthermore, both sensing systems use an active and a passive element to provide an output that is immune to external interfering magnets. To establish the dependability of the prototype, it was implemented and evaluated under various test scenarios. The second contribution of this research work has proposed, analyzed, and evaluated a contactless wake-up circuit for an MCU that makes use of a light-emitting diode (LED) operating as a hotodetector and is lighted by a smartphone flashlight. The circuit comprises a high-pass filter and a voltage-level translator that connects the LED to the MCU through an appropriate resistor in parallel. When lighted by a switching flashlight, the LED produces a square voltage, which is translated into logic levels at the wakeup circuit output. A firmware embedded in the MCU also ensures that a specified series of logic pulses at a specific rate is received in order to activate the MCU. These additional stages make it more robust against ambient light interferences. Note that LEDs manufacturers do not disclose information regarding how LEDs respond to light. Consequently, this second contribution is complemented with the current-voltage characterization of several types of LEDs. Finally, in the third contribution, the energy challenge associated with the node’s power source is addressed. Specifically, the energy harvesting of radiofrequency (RF) signals present in the environment is chosen among all available energy sources. A compact Thévenin model for a rectenna is proposed in this study.The investigated rectenna comprises an L matching network and a halfwave rectifier. The developed model is simpler and more compact than those previously proposed in the literature, and it contains explicit and simple analytical expressions of the Thévenin voltage, resistance, and power efficiency. The experimental findings support the suggested model, demonstrating a linear current–voltage relationship as well as a maximum efficiency (60%) at -10 dBm. At the rectenna output, an MPPT was also employed to automatically work at the highest efficiency point, with an overall efficiency nearing 50% at -10 dBm. Further experiments were carried out, this time with a nearby transmitting antenna, to power a sensor node with a power demand of 4.2 µW. El Internet de las cosas es un tema tendencia en estos días. Sin embargo, la energía es a menudo el principal obstáculo para la adopción generalizada de esta tecnología, que tiene tres restricciones estrictas: es extremadamente orientada a los costos, requiere una larga vida útil y un tamaño pequeño. Como consecuencia, los desarrolladores deben superar muchos desafíos relacionados con la gestión óptima de la energía disponible para alimentar un nodo. Esta gestión no solo se limita a la fuente de alimentación, sino que también comprende el consumo energético inteligente del nodo. En este trabajo se abordan tres desafíos: el primero asociado con el sistema de detección del nodo, el segundo, con el consumo de energía cuando el nodo no está rn funcionamiento, y el tercero, con la recolección de energía. Las contribuciones de esta tesis se presentan como un compendio de artículos de tres publicaciones de revista y tres artículos de conferencias, donde cada publicación aborda uno de los desafíos. La primera contribución está relacionada con el sistema de detección del nodo. En particular, el sistema de detección de los contadores electrónicos de gas. Se ha desarrollado un nuevo sistema de detección para contadores de gas. Se basa en una detección magnética dual: a) detección primaria de bajo costo y baja potencia a través de interruptores de lengüeta conectados a entradas digitales del microcontrolador (MCU), y b) detección secundaria mediante sensores de efecto Hall acoplados a entradas analógicas de la MCU. Además, ambos sistemas de detección utilizan un elemento activo y uno pasivo para proporcionar una salida que es inmune a imanes externos que puedan interferir con la medición. Para corroborar la fiabilidad del prototipo, se implementó y evaluó en varios escenarios de prueba. La segunda contribución de este trabajo de investigación ha propuesto, analizado y evaluado un circuito de activación sin contacto para MCUs, que hace uso de un diodo emisor de luz (LED) que funciona como fotodetector y es iluminado por el flash de un móvil. El circuito comprende un filtro pasa alto y un traductor de nivel de voltaje que conecta el LED al MCU a través de una resistencia apropiada en paralelo. Cuando se hace conmutar el flash, el LED produce una señal cuadrada, que se traduce en niveles lógicos en la salida del circuito de activación. Un firmware integrado en el MCU garantiza que se reciba una serie específica de pulsos lógicos a una cierta velocidad para activar el MCU. Estas etapas adicionales lo hacen más robusto contra las interferencias de la luz ambiental. Se debe resaltar que los fabricantes de LED no divulgan información sobre cómo responden los LED a la luz. En consecuencia, esta segunda aportación se complementa con la caracterización corriente vs. tensión de varios tipos de LED. Finalmente, en la tercera contribución, se aborda el desafío energético asociado con la fuente de energía del nodo. Específicamente, la recolección de energía de señales de radiofrecuencia (RF) presentes en el medio ambiente se elige entre todas las fuentes de energía disponibles. En este estudio se propone un modelo compacto de Thévenin para una rectenna. La rectenna investigada comprende una red de adaptación L y un rectificador de media onda. El modelo desarrollado es más simple y compacto que los propuestos previamente en la literatura, y contiene representaciones explícitas de la tensión y la resistencia de Thévenin y la eficiencia energética. Los hallazgos experimentales apoyan el modelo sugerido, demostrando una relación lineal entre la corriente y la tensión, así como una eficiencia máxima (60%) a -10 dBm. En la salida de rectenna, también se empleó un MPPT para trabajar automáticamente en el punto de mayor eficiencia, con una eficiencia general cercana al 50% a -10 dBm. Se llevaron a cabo más experimentos, esta vez con una antena de transmisión cercana, para alimentar un nodo sensor con una demanda de energía de 4,2 µW.

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Experimental characterization of off-the-shelf LEDs as photodetectors for waking up microcontrollers

Cited by 4 publications

References 6 publications

Advances in Optical Based Turbidity Sensing Using LED Photometry (PEDD)

Advances in Optical Based Turbidity Sensing Using LED Photometry (PEDD)

LED-Based Wake-Up Circuit for Microcontrollers

Design and implementation of wireless nodes for the Internet of Things

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