Plant growth dynamic fill control system for initial construction of LED light source

Photosynthesis is the material basis for the metabolism and energy of all substances in the biological world. Plants reflect the original light photosynthesis and release the light energy in a large fluorescence mode. Therefore, chlorophyll fluorescence has a close relationship with photosynthesis. In the past 30 years, research on LED artificial light sources in facility horticulture, plant facility cultivation, and space agriculture has attracted widespread attention worldwide. The results of different light quality on plants such as strawberries and orchids show that red light has an important effect on plant morphology and plant height regulation, and promotes the growth process of leaves. The leaves, stems and petioles of plants will elongate. However, the chlorophyll content is low, and growth indicators and dry matter accumulation are also reduced. The regulation of photosynthesis by blue light mainly focuses on the opening of stomatal, the differentiation of chloroplasts and the regulation of photosynthesis enzyme activity. POSPA and other studies found that under the action of monochromatic blue LED, the chlorophyll content was the highest and the number of stomata was the most. At present, in the study of the photosynthetic physiological characteristics of plants by composite spectroscopy, the combination of red and blue LEDs can have a positive impact on the growth and development of plants. Due to the monochromatic light treatment, the system uses red and blue light combination as an auxiliary light source for tomato growth. The closed-loop control of the host computer, the programmable power control LED array and the MINIPAM modulation fluorometer is carried out by software to analyze the growth conditions of the tomato under the optimal illumination conditions.

1. The overall structure of the system

The dynamic fill light control system uses MINI-PAM to monitor the actual photosynthetic efficiency of tomato and LED combined light source fill light to guide the greenhouse tomato fill light production. The system consists of five modules. The upper computer decision module is an industrial grade server, developed independently. Designed STM32 single-chip greenhouse environmental factor monitoring system, providing a stable current JBP-7510 programmable constant current source for the fill light source, high-power red and blue LED combined light source and MINI-PAM modulated fluorescence detector. With the fluorescence parameters as the goal, the output current of the programmable constant current source is continuously adjusted in the greenhouse environment to change the illumination intensity of the LED combined light source, and then the fluorescence parameter ΦPSII of the tomato is changed to the expected value to achieve the effect of artificial regulation of tomato photosynthesis. The basic schematic diagram of the system is shown in Figure 1.

2. Monitoring system hardware design

2.1 LED combination

The power supply module JBP-7510 programmable control constant current power supply is the current power supply. Under the rated working condition, it can output a stable desired current. In order to accurately control the LED combined light source driving current and achieve the purpose of controlling the light source illumination condition, choose one. A very stable current source is very important. The programmable constant current source has a constant output current, so the current is not affected by the load, and the magnitude of the driving current directly controls the brightness of the LED lamp bead , so the current source can accurately control the light intensity of the LED combined light source. Programmable constant current source voltage output is up to 75V, voltage accuracy is 0.05%+37.5mV, current output is up to 10A, current accuracy is 0.1%+10mA, and the appropriate fill light current value is calculated according to the fluorescence parameter upper computer. The line communication sends instructions to the power supply, and finally the programmable output current provided by the constant current source drives the LED combination light source.

The JBP-7510 programmable control constant current power supply tests the control current and the actual current when the LED fill light source is driven at room temperature 25 degrees Celsius. The 12 data in the test results are shown in Table 1. From the data result analysis, the current accuracy is better than ±0.2%, so the JBP-7510 programmable control constant current source current accuracy can meet the output precision of the system fill light current.

2.2 LED array design

By using the characteristics of LED light concentration and direction fixation, it is necessary to make reasonable planning, optimization and improvement to make the red and blue LEDs uniform in the illumination area. The complementary light of tomato is mainly used for red and blue LEDs. The designed combined light source should ensure the uniformity of red and blue light in the light received by tomato. The ratio of red and blue LEDs of the two design schemes is 1:1 and 4:1. : The ratio of red and blue LEDs is 1:1, the LEDs are evenly spaced, and the spacing between adjacent LEDs is 10mm. The array is shown in Figure 2(a). Array 2: The ratio of red and blue LEDs is 4:1. The red LED and blue LED form an area, and the blue LED is at the center. The array is shown in Figure 2(b).

2.3 MINIPAM modulation fluorescence detector

The MINIPAM pulse-modulated chlorophyll fluorescence instrument is manufactured by WALZ Co., Ltd., and the system uses the correlation fluorescence value of the steady-state fluorescence yield Fs under plant light adaptation and the maximum fluorescence yield Fm under light adaptation. Through the RS-232 interface and the host computer for two-way communication, the host computer closed-loop control MINIPAM and LED lighting array.