LED Technology
How to use add-on boards to build a powerful IoT-based greenhouse LED lighting and sensor system
I
n horticulture, the Internet of things (IoT) can play a key role in both monitoring and ensuring plant health, using a combination of sensors and specialised horticulture LEDs. However, adapting and implementing the right IoT computing platform can be time consuming and put both budgets and schedules at risk. To reduce this risk, a combination of board and device solutions can be used to greatly simplify the design process while at the same time allow the rapid development of sophisticated greenhouse control systems. This article by Stephen Evanczuk, Digi-Key, will explore the relationship between LEDs and plant health and offer solutions explaining how to use them together. 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 (Figure 1).
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
Figure 2: The PSoC Pioneer IoT add-on shield (red board) extends the capabilities of Cypress Pioneer boards such as the PSoC 6 BLE Pioneer Kit (blue) with its multiple connector options for adding off-the-shelf Qwiic and XBee-compatible boards. (Image source: SparkFun Electronics)
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 and 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
Figure 3: Small changes in pH level affect plant physiology directly, as well as indirectly through its impact on nutrient availability in soil. (Image source: Wikimedia Commons)
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.
Figure 1: Plant growth depends on sufficient illumination at wavelengths corresponding to the absorption spectra of various photopigments active at different segments of the overall photosynthetic active radiation (PAR) region. (Image source: Wurth Electronics)
12 February 2020 Components in Electronics
High-performance platform Designed for embedded applications, the Cypress PSoC family of microcontrollers integrates an Arm Cortex-M0 or Cortex-M3 core, and a full complement of programmable analog and programmable digital blocks called universal digital blocks (UDBs). Using the Cypress peripheral driver library (PDL), designers can use UDBs to implement a wide range of functions, including standard serial interfaces and waveform generators. Similarly, programmable I/O blocks called Smart I/O, support logic operations on signals passing to and from the GPIO pins, even while cores are in a power saving, deep sleep mode. The latest PSoC device, the PSoC 6, extends the family with dual-core devices that combine the processing performance of a Cortex-M4 core with the low power capabilities of a Cortex-M0+ core. Along with the 1 megabyte (Mbyte) of flash memory, 288 kilobytes (Kbytes) of SRAM, and 128 Kbytes of ROM found in PSoC 62 devices, the PSoC 63 devices add additional capabilities, such as Bluetooth 5.0. The PSoC 63 devices integrate a
complete Bluetooth 5.0 subsystem including hardware physical and link layers, as well as a protocol stack with application programming interface (API) access to the generic attribute profile (GATT) and the generic access profile (GAP) services at the heart of Bluetooth protocols. Within each series, devices such as the CY8C6347FMI-BLD53, include dedicated hardware crypto accelerators. With their extensive capabilities, PSoC 6
microcontrollers are able to support the performance requirements of an emerging class of complex embedded applications. At the same time, their power efficiency enables them to support the tight power budgets typically found in these applications. With its user-selectable 0.9 or 1.1 volt core operating voltage, the PSoC 6 microcontroller requires minimal power, consuming 22 microamps ( A) per megahertz (MHz) for the Cortex-M4 core, and 15 A/MHz for the Cortex M0+ core. To simplify development of applications based on these devices, Cypress provides versions of its Pioneer kit line for both PSoC 63 and PSoC 62 devices. Based on the PSoC 63, the PSoC 6 BLE Pioneer Kit includes a 512 Mbit NOR flash, Cypress's KitProg2 onboard programmer/debugger, a USB Type-C power delivery system, and multiple user interface features. The PSoC 6 Wi-Fi-BT Pioneer Kit combines a PSoC 62 microcontroller with a Murata Electronics LBEE5KL1DX module, which is based on the Cypress CYW4343W Wi-Fi/Bluetooth combo chip.
Hardware extensions Using the Cypress Pioneer boards to develop process control applications becomes easier thanks to an add-on board developed through a collaboration of
www.cieonline.co.uk
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