How to rapidly build powerful IoT-based LED lighting & sensor systems for greenhouses

Author : Rich Miron | Applications Engineer | Digi-Key Electronics

01 May 2019

Digi-Key_IoT-based LED lighting & sensor systems for greenhouses
Digi-Key_IoT-based LED lighting & sensor systems for greenhouses

In horticulture, the IoT can play a key role in both monitoring & ensuring plant health, using a combination of sensors & specialised LEDs. However, adapting & implementing the right IoT computing platform, with the required peripherals, sensors, LEDs & connectivity options, can be time consuming and put both budgets & schedules at risk.

This tutorial was originally featured in the Digi-Key Article Library and in the May 2019 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.

Here, Rich Miron, Applications Engineer at electronic components distributor, Digi-Key Electronics will explore the relationship between LEDs and plant health, before introducing and describing solutions to simplify the design process and allow the rapid development of sophisticated greenhouse control systems.

LEDs and plant health
Plant health depends on a wide range of external factors, including light, temperature, soil moisture content and pH levels. They respond to various combinations of these factors in aggregate, as well as to the specific characteristics of each factor. For example, a plant depends upon light received within a photosynthetic active radiation (PAR) region lying between 400 nanometers (nm) and 700 nm. Yet, the illumination they require across that region is by no means uniform. Instead, plants require light at specific wavelengths corresponding to the absorption spectrum of the multiple photopigments involved in photosynthesis.

For example, chlorophyll A has absorption peaks at approximately 435 nm and 675 nm. Other photopigments, including chlorophyll B, beta carotene and other photochromes, also serve vital roles in photosynthesis. As a result, optimal illumination for plants requires the ability to deliver illumination at multiple wavelengths in the PAR region.

As with any living organism, the factors that influence health in plants are not limited to a simple set of wavelengths or static illumination levels. Plants require different levels of light intensity, varying light/dark cycles and even different wavelength combinations, all at each stage of the growth cycle. Similarly, temperature and soil moisture content can cause variations in root length.

This optimal combination of characteristics for each factor can vary across different species, or even across different stages of growth within a single species. For example, many flowering plants require day length less than about 12 hours. In contrast to these ‘short day’ plants, ‘long day’ plants such as beets and potatoes only flower after exposure to more than 12 hours of light.

Greenhouse environments enable farmers or backyard gardeners to control most of the factors. Yet, the lack of cost-effective system platforms, peripherals and even suitable light sources has remained an obstacle to development of greenhouse control systems. Building a system capable of monitoring and managing these various factors has required complex systems akin to complex industrial programmable logic controllers.

The availability of off-the-shelf boards and specialised horticulture LEDs offers a simpler alternative. Developers can easily create sophisticated greenhouse automation systems by combining boards based on Cypress Semiconductor’s PSoC microcontroller, specialised horticulture LEDs from Wurth Electronics, and an add-on board from SparkFun Electronics. The latter ties in the broad set of sensors and actuators needed in these systems.

To read the full version of this tutorial, visit the Digi-Key Article Library or read EPDT magazine's May 2019 digital issue.

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