In applications such as smart buildings, smart homes and Industry 4.0, various sensors and Internet of Things devices need to be widely deployed. If these devices are powered by ordinary batteries, there will be a problem with battery replacement. If they can be powered by solar cells, the trouble with battery replacement can be eliminated and their usefulness greatly improved. This article will show you the development of solar cells and the functions and features of the solar cell multi-sensor platform launched by onsemi.
Solar cell technology has developed rapidly
Solar power generation is renewable and environmentally friendly power generation, which will not produce greenhouse gases, such as carbon dioxide, in the process of power generation and will not pollute the environment. It is currently one of the most popular renewable energy power generation methods. A solar cell converts sunlight into electric energy through photovoltaic effect. It is a photoelectric semiconductor sheet that directly generates electricity by sunlight, also known as "solar chip" or "photocell". As long as it meets the illumination of certain illumination conditions, it can instantly output voltage and generate current in the case of loop.
Simply put, the power generation principle of solar photoelectricity is a power generation mode that uses solar cells to absorb sunlight with wavelength of 0.4μm - 1.1μm (for crystalline silicon) and directly convert light energy into electric energy for output. As the electricity generated by solar cells is direct current, it is necessary to install a DC/AC converter and replace it with alternating current to supply electricity to household or industrial appliances.
Most solar cells have problems in charging consumer goods. In the past, nickel-metal hydride or nickel-cadmium batteries were generally used for charging, but nickel-metal hydride batteries could not resist high temperature, and nickel-cadmium batteries had environmental pollution problems. At present, super capacitor develops rapidly, its capacity is super large, its area is reduced and the price is low. Therefore, some solar products begin to adopt super capacitor as charging object, thus improving many problems of solar charging.
Solar cells solve the problem of power supply for devices
In applications such as smart buildings, smart homes and Industry 4.0, various sensors and Internet of Things (IoT) devices must be used to collect and transmit environmental data. These devices usually need to be powered by batteries or mains power, which brings a lot of trouble when deploying these devices. After all, these devices may have to be deployed outdoors where commercial power is not easy to reach. If general batteries are used for power supply, even if the devices are extremely power-saving, the battery will eventually run out. At this time, we must spend manpower and time to replace the battery, which poses considerable challenges to the usefulness of these devices.
Solar cells will solve the power supply problem between these sensors and IoT devices. Once solar panels receive sunlight, they can carry out photoelectric conversion, and store excess power in batteries, so as to continuously supply power to devices at night. As a result, these devices will no longer have power supply problems, which will result in significant savings in construction costs for applications such as smart buildings, smart homes and Industry 4.0.
Battery-free solar cell multi-sensor platform
For solar cell applications, onsemi introduced the RSL10 solar cell multi-sensor platform (RSL10-SOLARSENS-GEVK), which is a comprehensive development platform for battery-free Internet of Things applications in vertical fields such as smart buildings, smart homes and Industry 4.0. It is a complete set of low-cost solutions for developing and using sensor nodes that collect solar self-power. It is based on the RSL10 SIP (System-in-Package), the industry's lowest power Bluetooth® 5 radio, and the RSL10 solar cell multi-sensor platform supports continuous BLE (Bluetooth Low Energy) without a battery to transmit sensor information. This fully integrated platform has multiple smart sensors for environmental and motion sensing, including an ultra-low quiescent current LDO regulator (NCP170) and a 2-port connector for solar cells also include a low weight, thin 47 μF storage capacitor, as well as a programming and debugging interface, and a connected solar cell.
As the platform can obtain energy from low-current sources, it is important to minimize leakage of the system during operation and standby. Together with other energy-saving devices, the ultra-low static current LDO(NCP170) on the circuit board can significantly reduce the leakage. In standby mode, the power consumption is 55 nw, Rx is 10 mW, Tx is 0 dbm, and it can support Beacon and telemetry transmission. It can be completely reprogrammable by using the SEGGER J-Link with Arm® Cortex® debug connector (10-pin) adapter, with ultra-low leakage, adaptive duty cycle (self-detection of transmission energy availability), and dual solar cell interface (through-hole wire soldering or ZIF interface).
The RSL10 solar cell multi-sensor platform is equipped with a variety of ultra-low power smart sensors, including low-voltage and high-precision temperature sensor (NCT203) with wide temperature range (-40 to 125℃), combined digital humidity, pressure and temperature sensor (BME280), and smart 3-axis ultra-low power accelerometer (BMA400) with integrated wake-up and sleep functions, pre-flashed interweaving Beacon firmware, including the Eddystone TLM Beacon, supporting broadcast storage capacitor voltage level, temperature, time since power-on and advertising data packets since power-on, compatible with the BLE Scanner application (iOS® or Android™), and also supporting custom environmental service Beacon, and supporting broadcast temperature, humidity and pressure, and providing software library and examples in the B-IDK CMSIS-Pack to support a wide range of lighting conditions (artificial light or sunlight, as low as 180 lux).
The panel is powered by a solar cell, the Panasonic Amorton AM−1522 by default, and typically operates at 3V. The circuit is protected by 3V clamp, and the operating range is 1.6V to 2.65V. When it is lower than 1.6V, it does not allow transmission, and the device is harvesting energy; when the voltage is above 2.65V, the device starts to operate and depletes the energy buffer to 1.6V.
The RSL10 solar cell multi-sensor platform can be widely used in smart homes/buildings, environmental sensing (heating/cooling, air quality), intruder detection, ambiance and climate control, Industry 4.0/smart city, worker safety and fall detection, air quality monitoring, smoke detection, mobile personal care, integrated/portable sensors, smart safety helmets (bicycles, motorcycles) and other fields.
A variety of low-power devices and development tools to build a development platform
The RSL10 solar cell multi-sensor platform adopts many important devices, including the RSL10 radio frequency transceiver introduced by onsemi, which is a radio SoC and supports Bluetooth® 5.2 certification. With the SDK 3.7, RSL10 can bring ultra-low power BLE to wireless applications, support advanced wireless functions, and optimize system size and battery life. Highly integrated radio SoC adopts dual-core architecture and 2.4 GHz transceiver, which can flexibly support BLE and 2.4 GHz custom protocol. The Software Development Kit (SDK) of RSL10 allows rapid development of ultra-low-power BLE applications by leveraging from Blinky for convenient abstraction, drivers, and samples to complete BLE peripherals and the tools needed between the two.
The main features of its SDK include free onsemi IDE based on Eclipse®, support for Keil μVision® and IAR Embedded Work Bench®, complete BLE protocol stack, FOTA (firmware over the air) with Android™ and iOS applications, and support for FreeRTOS™.
In terms of smart sensors, the BMA400 triaxial accelerometer from Bosch Sensortec is the first real ultra-low power accelerometer. The BMA400 is especially suitable for wearable devices requiring long battery life. In addition, it is an ideal solution for smart home applications, such as smart indoor climate system and smart home security system. By distinguishing critical situations from false signals, the new accelerometer can avoid false alarms.
Bosch Sensortec's BME 280 is a humidity sensor that measures relative humidity, barometric pressure and ambient temperature. It was specially developed for mobile applications and wearable devices where size and low power consumption are key design parameters. This device combines high linearity and high accuracy sensor, which is very suitable for low current consumption, long-term stability and high EMC robustness. The humidity sensor can provide extremely fast response time, thus supporting the performance requirements of emerging applications, such as context awareness and providing high-accuracy sensing over a wide temperature range.
The NCT203 temperature sensor from onsemi is a digital thermometer and under temperature/overtemperature alarm, which is designed for thermal management systems requiring low power consumption and size. The NCT203 operates from 1.4V to 2.75V, making it available for a wide range of applications including low-power devices.
onsemi's NCP170 series of CMOS low dropout (LDO) regulators are designed specifically for portable battery-powered applications which require ultra-low quiescent current. The ultra-low consumption of typical 500 nA ensures long battery life and dynamic transient boost feature improves device transient response for wireless communication applications. The device is available in small 1 × 1 mm xDFN4, TSOP5 and SOT-563 packages.
Conclusion
In recent years, solar cells have seen accelerated development, including faster charging, longer service life, wider charging temperature range, and reduced solar cells (which can be charged at low voltage), making them much more useful. onsemi's RSL10 solar cell multi-sensor platform introduced in this article, combined with solar cells, will provide continuous power for various sensors and Internet of Things devices, and solve the power supply problem of devices in applications such as smart building, smart home and Industry 4.0. Its market and application will have great space for development, which will interest a great many people.