luXbeacon: An Open Source Platform for Energy Harvesting BLE Beacon DevelopmentFollow article
With the advent of manufacturing technologies for low-cost computation and communication devices, the Internet of Things, a new paradigm for a communication system, was introduced.
Bluetooth low energy (BLE) beacon is one of the most prospected building blocks for the Internet of Things, an infrastructure that will support various user-aware/-centric applications. However, because these BLE beacons are battery powered, a periodic battery replacement and management operation are imperative. To address this issue, this article presents an open source hardware design, an energy harvesting BLE beacon platform, luXbeacon, that will pave a way to a green and self-sustaining infrastructure for the Internet of Things era.
luXbeacon is an energy harvesting BLE beacon platform designed and developed by the research team in HKUST-NIE Social Media Lab. luXbeacon harvests ambient light energy to power it's onboard PMIC and BLE SoC, and also charge 1.5F supercapacitor to enable perpetual operation even in absence of light sources. Therefore, it can support battery-free operations even in indoor environments where the ambient light energy is scarce. Moreover, the luXbeacon design is open sourced, and the corresponding circuit and casing designs and source code for the firmware can be downloaded at luXbeacon website.
However, since most of the original luXbeacon development was done on a paid ECAD designing software, the released source files were not easily accessible to the public. To address this issue, the luXbeacon design was converted to a free ECAD software, DesignSpark PCB, along with few upgrades that prove to have a significant improvement in luXbeacon’s performance, namely the operational lifetime. This DesignSpark PCB version of luXbeacon is henceforth called HKUST luXbeacon. The article aims to provide a brief overview of luXbeacon’s circuit and firmware design to establish a basic understanding of the working principles of luXbeacon.
HKUST luXbeacon Hardware
Fig. 1. Block diagram of HKUST luXbeacon hardware design
The luXbeacon hardware design is largely divided into two sub-systems; power management and Bluetooth communication system. The power management system consists of a power management IC, 3.3V regulator, 1.5F supercapacitor, and a solar panel. The power management IC routes the harvested power to the entire circuit in an appropriate manner to ensure continuous operation of the BLE SoC and alleviate the cold-start problem. Moreover, our luXbeacon design ensures startup time under 15 seconds in an indoor lightings environment of around 100 lux light intensity.
The supercapacitor is employed as the rechargeable energy storage instead of the widely used lithium-ion rechargeable battery to allow efficient and quick charging of the energy storage in an indoor environment. Although the rechargeable battery offers superior energy density, it is observed that the energy harvested from the indoor lighting, which is around 40 uA at 3V, is simply insufficient to charge up the battery.
A step-down voltage regulator is employed between the output of the PMIC and BLE SoC to provide a fixed voltage to power the SoC and increase the energy storage capacity of the supercapacitor. Furthermore, having a regulated voltage source of 3.3V would make adoption of I2C-enabled sensor modules easy. This is a newly added component in HKUST luXbeacon. Through the experiments, we have observed that the HKUST luXbeacon could extend the lifetime of the supercapacitor by 33%.
Fig. 2 - 4 below presents the schematics of HKUST luXbeacon, PCB design, and the actual prototype of the design.
Fig. 2. Schematic of Bluetooth sub-system of HKUST luXbeacon.
Fig. 3. Schematic of power management sub-system of HKUST luXbeacon.
Fig. 4. PCB design and prototype of HKUST luXbeacon.
HKUST luXbeacon Firmware
One of the most important operating parameters of a BLE beacon is the advertising interval. The advertising interval determines the broadcast frequency or the time interval between each broadcasting event. To allow the HKUST luXbeacon to adapt to varying energy harvesting rate, a Dynamic Advertising Interval Algorithm (DAIA) was implemented to make the energy usage flexible by varying the advertising interval depending on the supercapacitor level. This allows the BLE SoC to stop advertising automatically and operate in sleep mode when it senses that the stored energy in the supercapacitor is almost used up. Through the experiments, we observed that the lifetime of the HKUST luXbeacon was improved by 25%.
The block diagram of the DAIA is shown below.
Fig. 5. Block diagram of DAIA for HKUST luXbeacon.
Real-life Deployment and Use Cases
To prove the practicality of luXbeacon, we have conducted multiple field-tests with our industry partners. We have deployed the luXbeacon in Bangkok, Thailand for proximity marketing purpose as shown in Fig. 6. Here, the luXbeacon was deployed in a semi-outdoor environment where it could harvest sunlight during the day and led lamp lights during the evening time. However, after midnight, it would have to survive until dawn with the stored energy in its supercapacitor.
Fig. 6. Deployment of luXbeacon in Bangkok, Thailand for a proximity marketing application.
We have also deployed the luXbeacon in INNOCentre, Hong Kong, for indoor navigation application as shown in Fig. 7.
Fig. 7. Deployment of luXbeacon in INNOCentre, Hong Kong, for an indoor navigation application
We have also deployed the luXbeacon in EMSD headquarters, Hong Kong, for indoor localization application as shown in Fig. 8. The luXbeacons were deployed very close to the light source and proved to be able to support batteryless operation with 0.1 s advertising interval, which is very power consuming.
Fig. 8. Deployment of luXbeacon in EMSD headquarters, Hong Kong, for indoor positioning application.
In the recent few years, Bluetooth low energy beacon rose as a viable option for various Internet of Things and smart city applications. However, it's limited battery lifetime and the necessity of periodic maintenance and battery replacement operations discouraged some from adopting this new technology. To solve this problem, our team at HKUST Social Media Lab., came up with an energy harvesting BLE beacon design that can self-sustain even in indoor environments. Furthermore, this design was transferred into DesignSpark PCB platform as an open source design initiative for others to access and further develop this innovative design. The luXbeacon initiative opens up numerous possibilities and opportunities for students, researchers, and hobbyists to come up with their own versions of luXbeacon, accelerating the developments for green and sustainable IoT infrastructure. Hopefully, we will see more of luXbeacons deployed across our cities to not only make them smart but also green.
The luXbeacon initiative was sponsored and supported by RS components, HKUST-NIE Social Media Lab., HKUST ECE Dept., and EMSD. The HKUST luXbeacon was designed and developed with help from Alex Choi and Ivan Yeung.
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