Plant lighting system design

1. Functional target design of plant lighting system

This paper intends to design a plant lighting system integrating monitoring, management and control. The overall goal of the design is to realize an easy-to-use, efficient and reliable energy-saving plant lighting system. Plant lighting needs to focus on the following factors:

(1) Light intensity: The light intensity determines the photosynthesis effect of plants. With the increase of light intensity, the speed of photosynthesis will be accelerated until it is saturated. Photosynthesis is a key process in the growth and development of plants, so light intensity has a great impact on plants, and plants can grow well only under appropriate light intensity.

(2) Light quality (spectral distribution): Plants do not absorb light of all wavelengths in sunlight, they selectively absorb light of corresponding wavelengths according to needs. Plants mainly rely on chlorophyll and carotenoids to absorb light energy. The distribution of the absorption bands is shown in Figure 2-1. It can be seen that the absorption rate of plants is the highest in the red and blue light regions, while the absorption rate in the rest of the bands is low. So in photosynthesis, plants absorb the most red and blue light.

(3) Photoperiod: Photoperiod refers to the requirements of plants for the alternating appearance of light cycle (sunshine time length) and dark cycle (night time length), and photoperiod also affects the growth and development of plants. Photoperiod mainly affects plant flowering, and the formation of plant flower buds needs to meet its requirements for photoperiod. For some plants, the longer the light time, the earlier the flowering.

In order to better cultivate plants, the plant lighting system needs to be able to match and adjust the light intensity, light quality and photoperiod accordingly. In summary, the specific functional goals of the system are designed as follows:

(1) Appropriate light source. In order to meet the needs of plants for light quality and light intensity, the light source should match the spectrum required by plants as much as possible, and can reach the light intensity at the saturation point of plant photosynthesis. At the same time, the light source also needs to consider energy saving and environmental protection, so as to reduce the energy consumption of the system and the pollution to the environment.

(2) Flexible lighting control. The system needs to be able to control the light intensity and photoperiod to meet the lighting needs of different plants or the same plant at different growth stages. At the same time, plant lighting systems often have a large range and many light sources, so in addition to single-point control, the system should also support multi-point control.

(3) Simple and efficient control method. For plant lighting systems that often have a large scale, traditional wired switches or controllers are not only difficult to install and maintain, but decentralized control also leads to low efficiency and high labor costs. Therefore, the system needs a simpler and more efficient control method.

(4) Simple and real-time environmental monitoring. In addition to light requirements, environmental factors such as light intensity, temperature and humidity, and CO2 concentration are also extremely important to the healthy growth of plants. Staff need to understand the environmental conditions in a timely manner and take corresponding measures. Therefore, in order to save labor costs, reduce the complexity of the environmental monitoring system, and reduce human error rates, the system needs to digitize and centralize these environmental parameters to achieve simple and real-time environmental monitoring.

(5) Multiple control methods that can be expanded. In order to meet the needs of various occasions, the system should preferably support various control terminals such as mobile phones, computers, and pads, as well as local and remote management and control.

Among them, the first three constitute the main functions of the plant lighting system, and this article will focus on the design and implementation of the first three.

2. The overall frame design of plant lighting system

According to the functional target design in the previous section, the system needs to have a simple and efficient control method, and the wireless control technology supports remote and centralized control and can save installation and maintenance costs, which just meets the functional target. Therefore, this paper designs and uses wireless communication technology in system control.

The system is mainly composed of three parts: lighting system control center, controlled nodes and wireless communication lines. The controlled nodes include lamp nodes and sensor nodes to support lighting control and environmental monitoring. The control center is composed of single-chip microcomputer, wireless communication module, Ethernet module and serial port module, etc. It is the core of the system, and its main function is to effectively manage and control the entire lighting system. The serial port module is designed to provide a direct access interface for the PC control terminal, while the wireless communication module is designed to provide direct access and control access for control terminals such as mobile phones and pads. The system can expand the network through the Ethernet module, such as providing remote cloud control, web-based network control, etc.; multiple plant lighting systems can also be networked to provide long-distance or large-area distributed management and control.

Various functions of the plant lighting system are realized by controlled nodes. The wireless communication technology is used to establish a connection between the control center and the controlled nodes, so the system can realize the information acquisition and control of each node in a centralized control manner. In addition, the control center provides a variety of communication interfaces for control terminals such as mobile phones and computers. The system can be easily managed and controlled through mobile phones, computers and other control devices, and has strong scalability.

3. Selection of light source for plant lighting system

The light sources used for plant lighting mainly include incandescent lamps, high pressure sodium lamps, fluorescent lamps, metal halide lamps and LEDs.

Incandescent lamps were the first artificial light source used to alter the photoperiod of plants. But incandescent lamps have high energy consumption and low efficiency, because photosynthetically active radiation only accounts for 15% of electric energy consumption, and the remaining 85% is dissipated as far-infrared light and heat. High-pressure sodium lamps are widely used as supplementary light sources in plant lighting due to their long life and suitable spectrum. However, only 30% of the electrical energy is converted into light by the high-pressure sodium lamp, and 70% of the electrical energy is converted into heat and lost. High-pressure sodium lamps generally work at high temperatures (≥200˚C), which will produce obvious infrared heat radiation in the environment. Therefore, high-pressure sodium lamps cannot be placed close to plants, and a corresponding ventilation system is required to avoid excessive temperature of the environment. This characteristic limits the development of high pressure sodium lamps in plant lighting.

The electro-optical conversion efficiency of metal halide lamps is lower than that of high-pressure sodium lamps, only about 24%, but its spectrum is better than that of incandescent lamps and high-pressure sodium lamps, and it is more suitable for the growth of plants. Fluorescent lamps do not provide light in the far-infrared spectrum, which prevents long-day plants from flowering. Moreover, the light intensity of fluorescent lamps is lower than that of high-pressure sodium lamps and metal halide lamps, resulting in low yield when used for plant lighting, which greatly limits the application of fluorescent lamps in plant lighting.

Compared with the above-mentioned plant lighting sources, LED has the following advantages:

(1) More flexible and matched spectra. The monochromatic high-power LED light source has a narrow-band spectrum, and the spectral width range is about 20nm. The spectrum of monochromatic LEDs can cover all visible light spectrum from blue light to red light, which can accurately match the absorption spectrum of plants, and the effective utilization rate of light energy can reach 80% to 90%, making it play an important role in the field of plant lighting.

(2) Higher light intensity. LED lighting systems can be configured to produce very high light levels, even well beyond daylight if required. But unlike high-pressure sodium lamps, they can be placed near plants even under higher light intensities, because LEDs convert most of the energy into light energy, the radiant heat generated during work is low, and waste heat can pass through The active heat sink is separate from the light-emitting surface.

(3) Longer service life. According to the test, the service life of the LED light source is more than 50,000 hours. If it is used reasonably, this may still be a conservative figure. It can be seen that a reasonably designed LED lighting system can have a life span beyond any traditional light source.

(4) The brightness is easy to adjust. As solid-state lighting, LEDs are easily integrated into digital control systems. The brightness of the LED can be continuously adjusted between zero and maximum brightness by digital dimming.

(5) Lower cost. LED has less maintenance cost and electricity cost. Traditional light sources have fragile filaments, electrodes, or gas-filled pressurized lampshades that must be replaced periodically. LEDs have no filament and no ballasts required to work with gas light sources, and they also have a longer lifespan in comparison, thus saving the purchase and maintenance costs of replacement bulbs. LEDs are also more energy-efficient, and 150-watt high-pressure sodium lamps have been tested to produce the same horticultural lighting effects as 14-watt LEDs.

(6) Environmental protection. LED does not contain mercury that will pollute the environment, and does not produce harmful substances during use. Because the effective utilization of LED light energy in plant lighting is high, it only needs to provide lower light intensity to achieve the same effect as other light sources, reducing light pollution.

In summary, according to the design purpose of system energy saving, environmental protection, high control efficiency and matching the requirements of plant lighting on spectrum and light intensity, this system will use LED as the light source of plant lighting, and the corresponding dimming scheme will be given below.

4. The dimming scheme of the light source of the plant lighting system

There are three commonly used dimming methods for LEDs: linear dimming, analog dimming and digital dimming. The three dimming methods are introduced as follows:

(1) Linear dimming: As the forward current increases, the output light intensity of the LED will also increase and increase almost proportionally. Linear dimming uses this mechanism to adjust the brightness. Therefore, a variable resistor can be connected in series in the LED circuit for dimming, and the operation is very simple. But this method also has some disadvantages: first, the resistance will consume a lot of electric energy and convert it into heat energy and waste it, resulting in low utilization efficiency of electric energy in the circuit; second, the LED is usually driven by a constant current source, which is not suitable for this kind of dimming The third way is that while changing the brightness of the LED by adjusting the current, it may change the spectrum and color temperature of the LED, especially the LED that uses phosphor powder. When the current changes, the output light intensity of the LED also changes, but the thickness of the phosphor is fixed, so the properties of the light passing through the phosphor change.

(2) Analog dimming: also known as thyristor dimming, this method utilizes the characteristic that thyristor can change the input voltage. Specifically, when the thyristor is turned on, the change of the conduction angle can cause the change of the voltage waveform (the voltage will also change accordingly). The conduction angle can be adjusted through the internal integrated adjustable resistor, so the thyristor can be dimmed in this simple way. This dimming method only needs to add a thyristor dimmer to the circuit, and the installation is more convenient, so it is widely used. But this method also has its drawbacks: the voltage is prone to fluctuate during dimming, causing the LED to flicker and emit noise. At the same time, the change of the voltage waveform may cause electromagnetic interference to the power grid.

(3) Digital dimming: that is, pulse width modulation (PWM) dimming. This method uses the characteristics of LEDs to support fast switching (up to microseconds), and the brightness of the LED can be changed by changing the width of the pulse in each cycle. As shown in Figure 2-3, the power supply is a pulse constant current source. By adjusting the ratio (duty cycle) of the LED power-on time in a pulse cycle, different average voltages can be obtained, thereby obtaining different brightness. When using PWM dimming, the pulse frequency can easily be set above 200Hz. Due to the visual residual effect, the human eye does not feel the flicker when dimming. At the same time, when PWM dimming is used, it is driven by a constant current source, so there is no need to worry about changes in spectrum and color temperature caused by voltage fluctuations.

In a comprehensive comparison, the PWM dimming scheme has obvious advantages, which is more in line with the design requirements of the plant lighting system in this paper. First of all, the LED is always switched between normal working state and non-working state during PWM dimming, so there will be no problem of low energy utilization in linear dimming, and no spectral changes that may occur during analog dimming. At the same time, the regulation of the pulse waveform is very precise, so digital dimming can achieve precise dimming and has a large dimming range, which can well meet the requirements of plant lighting for flexible control of lights. Therefore, this article will use PWM as the dimming scheme of the system.

5. Selection of wireless communication technology for plant lighting

From the research and development of plant lighting systems, it can be seen that simple and centralized control with the help of wireless communication technology is the development direction of plant lighting systems in the future. At present, several short-range wireless communication technologies commonly used in the Internet of Things include ZigBee, Bluetooth, Wi-Fi, infrared connection technology (IrDA), ultra-wideband (UWB) and Z-wave, etc., and the transmission distance of IrDA and UWB is too short (not More than 10m) and there is no international standard, it is not suitable for plant lighting systems. The comparison of other wireless technologies is shown in the table below.

Among them, ZigBee and Z-wave have the lowest power consumption, and the battery life can last hundreds of days, greatly reducing the cost of manual maintenance; while Wi-Fi and Bluetooth are relatively high power consumption, and the battery can only last for a few days, so ZigBee and Z-wave are more suitable for industrial fields that are sensitive to power consumption. Comparing ZigBee and Z-wave, it can be found that ZigBee has obvious advantages: ZigBee uses standard protocols, while Z-wave uses private protocols; ZigBee's communication distance and transmission rate are better than Z-wave; ZigBee networking is more flexible, It can support various network topologies such as mesh, tree and star, and can adapt to more applications; in terms of network capacity, ZigBee is far ahead of other wireless technologies, and can support up to more than 60,000 nodes, which is enough for plant lighting networking needs. But ZigBee also has its disadvantages. The maximum transmission rate of ZigBee is relatively low, only 250kbps, while Bluetooth and Wi-Fi can reach 24Mbps and 54Mbps respectively. Compared with Bluetooth and Wi-Fi, ZigBeeb cannot directly communicate with control terminals such as computers and mobile phones. In order to take advantage of ZigBee's low power consumption and powerful networking, and make up for its disadvantages such as low transmission rate and inability to communicate directly with the control terminal, this article will use ZigBee/Bluetooth dynamic multi-protocol technology combining ZigBee and Bluetooth as a plant lighting system. The main wireless communication technology for the control center. ZigBee/Bluetooth dynamic multi-protocol technology will be introduced in the third chapter.

6. Plant lighting system hardware and software platform

6.1 Brief introduction of plant lighting system hardware platform

This system will use Silicon Labs' EFR32MG12P332F1024GL125 (hereinafter referred to as EFR32) chip as the main control chip. The EFR32 chip uses ARM32 Cortex-M4 as the core, the operating frequency can reach 40MHz, supports sleep and deep sleep modes, has the advantages of low power consumption, powerful functions, good real-time performance, and excellent data processing capabilities. The size of the RAM; its built-in wireless communication module has a maximum transmission power of 10dBm and a receiving sensitivity of -102.7dBm, which can provide excellent link budget and support ZigBee/Bluetooth dynamic multi-protocol technology, which can achieve wider range and more reliable Wireless communication. The chip contains up to 65 GPIO ports, has multiple UART, USART, I2C interfaces, SPI interfaces, timers and 12-bit ADCs, and can work in the temperature range of -40°C to 80°C. Wake up quickly.

6.2 Introduction to Plant Lighting System Software Platform

Micrium OS is a full-featured embedded operating system, its components are tightly integrated, but there are few dependencies between components, allowing developers to flexibly tailor applications according to application requirements. The system is based on the very successful μC/OS-III kernel. μC/OS-III is provided by Micrium Corporation. It is a preemptive multitasking real-time kernel with good portability, high efficiency, tailorability, and adaptability to various microprocessors. And μC/OS-III is highly configurable, supports round-robin scheduling of each task priority, supports an unlimited number of tasks and other kernel objects, and can flexibly enable or disable most components of the kernel to save space. The ROM space occupied by the kernel ranges from 6KB to 24KB, and the RAM occupied by the kernel usually ranges from 3KB to 4KB. Micrium OS is provided in the form of source code and provides rich technical documentation, which is very easy to use and develop. For these advantages, this system uses it as a software platform. The following will briefly introduce the main modules of Micrium OS.

(1) Task management. Different from the front-end and back-end systems that perform tasks sequentially, Micrium OS is a multi-task real-time operating system. The system abstracts different tasks, allowing developers to divide functions into multiple modules, and each task is responsible for a module. As shown in Figure 2-4, the system kernel allows multitasking. The execution order of tasks is determined by the preemptive scheduler. Once the task with higher priority is ready and in a runnable state, the preemptive scheduler will save the currently running tasks. The state of the lower priority task and switch to the higher priority task to run. Typically, the state of a task is saved on a stack and restored from the stack when execution can resume. The system supports multiple task synchronization mechanisms such as semaphores and mutexes, and inter-process communication between tasks is realized through message queues.

(2) Memory management. Traditional memory managers use memory allocation related functions to dynamically allocate and release memory, which is prone to memory fragmentation. In an embedded system, memory is very limited, so Micrium OS partitions continuous large blocks of memory, and sets a memory control block for each memory partition to dynamically manage it to overcome the problem of memory fragmentation.

(3) Time management. Timers alert the kernel using interrupts called ticks, which occur at a fixed frequency, with each tick ranging from 1ms to 100ms. In this time range, the kernel is allowed to provide task delay service, timeout control and time-based round-robin scheduling for applications. Micrium also supports the use of dynamic ticks, in which case the ticks don't run at a fixed frequency, and the kernel is only notified when there is a task, so the system can stay in a low power state without being periodically woken up.

Summarize

Firstly, the function target of plant lighting system is analyzed, and the frame structure of the system is designed. The main components of the whole system are control center, controlled nodes and wireless communication lines. After that, the light source selection and dimming scheme of the system were designed, and it was learned that LED is the most suitable light source for the system, and the corresponding optimal dimming scheme is PWM dimming. This chapter also compares wireless communication technologies, and selects the optimal ZigBee/Bluetooth dynamic multi-protocol communication method combining ZigBee and Bluetooth. Finally, the hardware and software platform used by the system are introduced.

The above are the details of the plant lighting system solution introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have the development and design needs of plant lighting systems, you can trust us. We have rich experience in custom development of electronic products. We can evaluate the development cycle and IC price as soon as possible, and can also calculate the PCBA quotation. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. Our development capabilities cover PCB design, single-chip microcomputer development, Bluetooth technology development, software customization development, APP customization development, WeChat official account development and other hardware and software design. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.