1.1 Introduction
A greenhouse is a place that can change the environment in which plants grow, create optimal conditions for plant growth, and avoid the effects of changing seasons and harsh weather. It uses light-covering materials as all or part of the structural material, which can be cultivated in winter or other seasons when plants are not suitable for open field. Greenhouse production aims to regulate the production period, promote growth and development, control pests and diseases, and improve quality and yield. The key technology of greenhouse facilities is environmental control, and the ultimate goal of the technology is to improve control and operational accuracy. With the development of agricultural modernization, facility agricultural engineering has received more and more attention from all countries in the world because of its wide range of disciplines, high technology content and close relationship with people's lives. This also provides an excellent opportunity for the development of China's large-scale modern greenhouses, and has a huge impetus. This project uses AVR chip as the control chip to design a set of lighting and carbon dioxide concentration control system suitable for current watermelon production.
1.2 Project Background / Motivation
As a big agricultural country, China's "three rural issues" are related to the quality of the people and economic development, and are related to social stability, national prosperity, and national rejuvenation. Modern agriculture is the top priority in the “Twelfth Five-Year Planâ€, and the situation of China’s agricultural production relying on the heavens has not changed fundamentally. Agricultural infrastructure conditions are still relatively poor, and the ability to resist natural disasters is weak. In recent years, China has lost about 100 billion kilograms of grain per year due to meteorological disasters. Natural disasters are on the rise, and food production risks are growing. Therefore, it is particularly important to reduce the impact of meteorological disasters on agricultural production while increasing the output of agricultural products.
Greenhouse is one of the essential facilities in modern watermelon production. Light and carbon dioxide concentration are two important factors affecting the growth and development of watermelon. Carbon dioxide is an important raw material for photosynthesis in plants. To maintain the photosynthesis of watermelon, the concentration of carbon dioxide should be kept at 250%-300%ppm. Light crops have two important coordinate points—the light compensation point and the light saturation point. The formation of photosynthetic products is related not only to the intensity of illumination but also to the time of illumination, ie the amount of illumination accumulated by a certain intensity. The more uniform the light distribution, the smaller the shadow area ratio and the light loss of the crop group, the higher the light energy utilization rate of the greenhouse crop. Therefore, controlling the amount of light and carbon dioxide is extremely important for greenhouse watermelon cultivation. This project uses the ATmega16 chip, combined with the light sensor, carbon dioxide sensor to achieve automatic control of greenhouse lighting and carbon dioxide.
Second, the demand analysis2.1 Functional requirements
The system first measures the light intensity, and controls the opening and closing of the related equipment according to the measured value of carbon dioxide under the corresponding illumination conditions and the highest and lowest values ​​of the environmental factors of the corresponding growth period. When the measured value is greater than the highest value or less than the lowest value, in addition to opening the corresponding device, the system also activates the alarm device to alert the staff. The system has the ability to measure the value of the displayed carbon dioxide concentration, and to connect to the execution device to perform automatic control, while leaving an interface to detect and control multiple environmental factors.
The light intensity of the greenhouse varies with geographical location and time. The light transmittance of different greenhouses is different, so the light distribution in the greenhouse is not uniform. Solar radiation is one of the main factors affecting the greenhouse environment. It can directly affect indoor temperature, humidity, photosynthesis and respiration of plants. According to the results of Dutch scholars, when the illumination is reduced by 19%, the yield is reduced by 21%. When the illumination is reduced by 32%, the yield is reduced by 34%, and the conclusion that 1% illumination equals 1% of the yield is obtained. The importance of crop growth.
In summer, the light intensity is too large. When the light saturation point is exceeded, it is necessary to artificially block the light to prevent the greenhouse temperature from being too high to burn the crop. The outer shade can be used for shading. In the rainy season and winter night, when the light intensity is lower than the light compensation point to shorten the effective illumination time of the crop, artificial light supplementation is required to promote crop growth. Commonly used greenhouse fill light artificial light sources mainly include incandescent lamps, halogen lamps, fluorescent lamps, high pressure mercury lamps, metal halide lamps and high pressure sodium lamps. In order to adjust the light quality and save energy, the metal halides and high-pressure sodium lamps are generally installed in the greenhouse in a ratio of 1:1.
Carbon dioxide is the main carbon source for plant photosynthesis. It is generally believed that the concentration of carbon dioxide is maintained at a suitable concentration of 500^-1000 (mg/kg). If it is as high as 3000 mg·kg, it will be harmful to the human body. The concentration of carbon dioxide in normal atmospheric conditions is 340350 mg/kg, and the photosynthesis rate increases with the increase of light amount, but tends to be moderate after reaching the light saturation point. In this case, the effect of temperature is not significant, but if carbon dioxide is applied to a concentration of 1000 mg/kg or more, the photosynthesis rate can be accelerated. However, there are compensation points and saturation points for the absorption of carbon dioxide by watermelon. The long-term concentration of carbon dioxide can cause damage to the photosynthetic system of watermelon and reduce the photosynthetic efficiency. Therefore, timely and accurate understanding of the concentration of carbon dioxide in the greenhouse is the basic condition for ensuring high quality and rapid growth of greenhouse watermelon.
The sources of carbon dioxide fertilizers in greenhouses are mainly carbohydrate fuels, high-pressure bottled carbon dioxide, dry ice, fermentation, organic matter degradation and chemical reaction formation, but most facilities are difficult to achieve automatic control. In the general greenhouse, a liquid carbon dioxide gas source in a steel cylinder is used, and the release and control time of the relay is used to realize the release of carbon dioxide. When the concentration of carbon dioxide in the greenhouse is too high, it can be adjusted by natural ventilation and forced ventilation. Provide them with a closed, good living environment that is more suitable for their growth. We first compiled a management schedule for the optimal environmental conditions for each stage of greenhouse watermelon storage, stored in the ROM of the AVR microcontroller, and the AVR microcontroller confirmed and corrected the parameters in each greenhouse according to the program table, and gave the terminal control system instructions. The terminal control device transmits the detection information to the AVR single-chip microcomputer, and outputs a control signal according to the instruction of the AVR single-chip microcomputer, so that the electrical machinery and equipment perform the action to realize the greenhouse environment adjustment. The system automatically controls the concentration of light and carbon dioxide.
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