The remote world of the IoT and building management systems (BMS) involves the connectivity of autonomous devices which require little or no maintenance – hence the term “Fit and Forget”. These “lonely” devices often consist of sensor/actuator functions which need power. The use of replaceable batteries or the provision of mains power is often not ideal due to location, cost and increasingly, user preference. To address this market need GSS, Sharp and the University of the West of Scotland (UWS) partnered to develop a self-powered wireless enabled CO2 sensor unit for environment monitoring, using Sharp’s energy harvesting technology. The development program is being supported by an Innovate UK grant.
Development Objective and Components
The objective was to develop an autonomous wireless CO2 sensing solution with integrated temperature, humidity and light measurements. The required platform had to self-power using energy harvesting techniques, and needed to perform at light levels down to 200 lux as is typically found in buildings, factories and homes. To support this requirement, the CO2 sensor node had to consume a miserly amount of power!
The GSS SmartIR NDIR CO2 gas sensors are based on mid-infrared, solid state light emitting diode (LED) and photodiode technology. Infra-red light is discharged from the LED and travels through the CO2 gas, bouncing round the inside of a horseshow-shaped light guide. The design of the light path provides enough distance between the LED and photodiode for the gas to absorb the infra-red light, which is important for ambient air environments where you’re measuring low concentrations of CO2.
With an energy per measurement requirement of just 6mJ, it’s ideal for extremely low power and wireless applications. The overall power consumption of the sensor can be adapted to the application by applying a sampling approach whereby the sensor is only switched on when taking a measurement. More detail on the GSS product range and the technology used can be found here.
Sharp’s Photovoltaic energy harvester is a new optoelectronic device optimised for florescent and LED indoor light. The device can harvest ambient light eciently down to as little as 10 lux and has the potential to drastically reduce or even eliminate the usage of batteries depending on the overall system requirements. The harvester array is capable of producing >20µW/cm2 at 200 lux, the 10 cm2 array used in the prototype produces circa 40µA at this light level. https://www.lightricity.co.uk/product-line-up
The Prototype System and result overview.
The prototype consists of the Sharp novel energy harvester, a charge management interface module, the GSS SmartIR CO2 sensor and a low power MCU/wireless module housed in a custom enclosure. The interface module manages the average and peak load power requirements of the storage element which can be either a rechargeable Li-ion battery or supercapacitor. The MCU module controls the various sensors and minimises system quiescent current. For this prototype activity, a proprietary wireless interface operating at 868Mhz was used. However the energy harvester powers supply module is capable of supporting state-of-the-art low power wireless formats such as LoRA, BLE, Zigbee etc. The energy harvesting system developed has proven that “Fit and Forget” self-powered, perpetual operation is achievable with the GSS CozIR® CO2 sensor at less than 200 lux.
For more information on our technology, and specifically our newly released upgrade of the CozIR®, the CozIR®LP – please contact [email protected]