Intelligent sensing for farmland: the Renesas system

Ken Imai, Senior Marketing Manager at Renesas, demonstrates a soil condition monitoring system that uses Energy Harvesting technology to provide the energy needed to manage the sensor and the resulting data (soil temperature and moisture).

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Renesas Energy Harvesting

To use pesticides, fertilisers and water efficiently, it is necessary to accurately measure the variations within the cultivated field. To ensure that the power supply for monitoring applications is also efficient, you can choose to recover energy from the environment.

Ken Imai_Renesas ElectronicsKen ImaiSenior Marketing Manager of Renesasillustrates a system of monitoring of soil conditions using Energy Harvesting technology to provide the energy needed to manage the sensor and the resulting data (temperature and soil moisture). The main component of the system is the Renesas RE01 microcontrollerwhich manages the available power at all times and integrates an Energy Harvesting controller. "First of all, we have to consider the energy balance available in the system and be able to power the microcontroller, the electronic components associated with the system, the sensors and the LoRa radio, which is the biggest contributor to energy consumption in this application.". The system must manage the energy collected from the environment, store it until the level is sufficient to read the sensors and send a message via radio to the host computer. The energy sources must then be selected. In this specific case, Matrix Industries' PowerSpike, a unique component that generates energy using Teg technology from the temperature difference between the subsurface (in this case less than 20cm below the ground surface) and the air on the surface, and Panasonic's AM1816CA solar cell were chosen.

System components 

The RE01 requires less than 35uA per MHz in active mode and only 120ns in standby mode. Its architecture consists of several internal and external domains, capable of working with a wide operating voltage range, allowing it to operate at 64MHz even at extremely low supply voltage levels. The RE01 also contains a wide variety of on-board peripherals, including a 14bit analogue-to-digital converter that can operate even when the entire device consumes less than 4uA. The Energy Harvesting controller can harvest energy from various renewable energy sources, charge external rechargeable batteries and super caps, and power external devices such as radios and sensors. In embedded Energy Harvesting applications, however, the problem of inrush current can arise, which is high and can cause the energy harvesting sources to collapse. With the RE01, on the other hand, power-up requires very little energy, just 5uA. Renesas then selected AVX's SCMQ14C474MRBA0 component to manage the power reserve and a Mercury family Dc-Dc converter from Matrix to convert the output from the Teg into a usable voltage. The Renesas HS3001, a high-performance humidity and temperature sensor ideal for developing smart applications in agriculture, was chosen as the main sensor. The LoRa radio selected is Dorgi's DRF1262G.

How monitoring works

The energy collected from the Energy Harvesting sources is stored in a super cap controlled by RE01. After 90 seconds, RE01 switches on and checks the level of energy stored in the super cap. If there is enough energy, then the sensors and radio switch on, the measurement is made and the data is transmitted via the LoRa radio. "The advantage of the system is that RE01 is able to switch on and initialise itself using its Energy Harvesting controller to handle the limited amount of energy available - a normal microcontroller would not be able to operate with such limited resources," comments Imai. The soil status monitoring system is currently being tested at various locations around the world to verify its reliability under real operating conditions.


Renesas sensorSensor for RH and T detection

The Renesas HS3001 sensor detects relative humidity and temperature and is an ideal solution for the development of smart applications in agriculture.
A built-in temperature compensation and calibration logic provides correct temperature (T) and relative humidity (RH) values via a standard I2C communication line. The sensor measures 2.41×3 mm. The measured data is internally corrected and compensated to provide accurate data within a wide range of temperature and humidity levels. The user also does not need to perform any calibration. The accuracy for the RH value is ±1.5%, for the temperature value ±0.2°C.

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