The project, backed by the UK’s InnovateUK R&D agency, uses the GSS SmartIR low power mid-range infrared sensor. The energy per measurement is just 6mJ and 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. The low power comes from using the mid-range IR LEDs developed and made by GSS that are specifically tuned to emit between 4.2 and 4.4 microns, making them highly energy efficient.
The aim of the project was to develop an autonomous wireless CO 2 sensing solution with integrated temperature, humidity and light measurements. The design 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.
The project used a new optoelectronic device optimised for florescent and LED indoor light from Sharp spin-off Lightricity which can harvest ambient light efficiently down to 10 lux and producing 20μW/cm 2 at 200 lux. The 10 cm 2 array used in the design produces around 40μA at this light level. The company was spun out of Sharp Laboratories of Europe in Oxford earlier this year to further develop and commercialise the technology. IT is working with Ilika and e-peas on power technology to support the solar cells.
The prototype consists of the Lightricity cells, a charge management interface module, the SmartIR sensor and a low power microcontroller and wireless module. 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, while the MCU module controls the various sensors and minimises system quiescent current.
The prototype uses a proprietary wireless interface operating at 868MHz to get the long lifetime, but the team say the wireless module is capable of supporting low power wireless formats such as LoRA long range wireless, Bluetooth Low