Design of intelligent adaptive intermittent light control system based on MSP430 single chip microcomputer

    In order to overcome the shortcomings of the existing supplementary lighting system, such as the inability to adjust the supplementary lighting time and the degree of supplementary lighting, and the inability to fully utilize the full spectrum for photosynthesis, the system is based on the MSP430 single-chip microcomputer and uses the principle that the rate of photosynthesis light reaction is greater than the dark reaction to improve the continuous supplementary lighting to intermittent supplementary lighting, avoid wasting light reaction products, and inhibit dark reaction; the photosensitive sensor circuit detects the current ambient light intensity, and sets the duty cycle to perform intermittent supplementary lighting to the light intensity most suitable for the growth of the plant; a high-brightness LED light group with a red: blue ratio of 5:1 is used to replace ordinary supplementary lights, which has a high spectral absorption rate. The system is innovative, efficient, and energy-saving, and is suitable for a wide range of applications in greenhouses, sheds, and homes.

    The traditional greenhouse lighting system will provide supplementary lighting when the light intensity is insufficient. The supplementary lighting time cannot be adjusted and is always on. Moreover, the degree of supplementary lighting is consistent and cannot be adjusted. In some cases, this will not only waste excess light and precious electricity, but also be detrimental to energy conservation and emission reduction. Moreover, if the sum of the light intensity in the external environment and the light intensity generated by the supplementary lighting exceeds the light saturation point of the plant, it will not only be of no help to the growth of the plant, but also inhibit the photosynthesis of the plant due to the excessive light intensity. Traditional supplementary lighting is usually white light, and most of the spectral energy in white light cannot be used by photosynthesis. The cost of traditional supplementary lighting is 0.6 yuan/kWh to meet the supplementary lighting of a 1 mx1 mx1 m space. If a month is calculated as 30 days, a normal power of 40 W will consume 28.8 kWh of energy for continuous irradiation for 1 month, and 5 lamps are needed, with a total electricity bill of 86 yuan. The price of 5 lamps is about 400 yuan, and the bracket and wires are about 30 yuan, totaling 516 yuan, which is beyond the affordability of most farmers and families. Therefore, traditional fill lights not only waste energy, but are also expensive and have poor applicability.

    This light control device can intermittently fill light according to the current ambient light intensity changes, fill light intensity to the light saturation point most suitable for the growth of the plant, and intermittently fill light with an adjustable duty cycle. The light saturation point can be set by programming. It uses a high-brightness LED light group with a red: blue ratio of 5:1 for fill light, and the photosynthesis utilization rate is optimal. It is simple to operate, highly efficient and energy-saving, low-priced, and widely used.

    1 System Hardware Design

    The hardware block diagram of the project system is shown in Figure 1.

    
    The system uses the low-power MSP430 series chip of TI Company in the United States as the main control module. The light intensity in the current environment is sampled through the lighting module with photoresistor as the core, and then the MSP430 series single-chip microcomputer is used to analyze and process it, so as to control the LED array fill light module with obvious fill light effect.
    In Figure 1, the device is connected to 220 V AC, and the 220 V AC is converted into 14 V DC through the adapter to power the photoresistor and LED light group. The photoresistor converts the light signal into an electrical signal, which is converted into a digital signal through the ACD analog/digital converter. The MSP430 series single-chip microcomputer samples it every 1 s and compares it with the preset value of the single-chip microcomputer program (assuming that the light saturation point is 18 kLux, and the light intensity of a group of LED lights at a distance of 1 m is 6 kLux). When the external light intensity is greater than 18 kLux, the lamp will not be turned on. When 12 kLux < light intensity < 18 kLux, the ⑥ single-chip microcomputer sends a lighting control signal to the ⑦ power amplifier to light one ⑩ lamp; when 6 kLux < light intensity < 12 kLux, the ⑥ single-chip microcomputer sends a lighting control signal to the ⑦⑧ power amplifier to light two ⑩ lamps; when the light intensity is < 6 kLux, the ⑥ single-chip microcomputer sends a lighting control signal to the ⑦⑧⑨ power amplifier to light three ⑩ lamps.
    Figure 2 is the legend of Figure 1 : (a) is a red LED lamp bead, (b) is a blue LED lamp bead, and the arrangement is shown in Figure 2.

    
1.1 Lighting module
    In the lighting circuit, VCC in MSP430 is used as the power supply of the lighting module. The electrical changes caused by the sensitivity of the photoresistor to light are used to compare and analyze the data stored in MSP430 through the MSP430 ADC sampling module to determine the current lighting conditions of the external environment. Then, in this case, the corresponding mode in the system that is most suitable for plant growth is selected. The plants are then supplemented with light through the fill light part of the project.
    The photoresistor used in the lighting module is GL5528. The specific circuit diagram is shown in Figure 3.

    
    The design idea of ​​this circuit is simple, easy to implement, and can basically meet the requirements in terms of accuracy.
1.2 The LED fill light module
    uses MSP430 to generate a control switch signal, which passes through the Darlington tube to make the Darlington tube work in a switch state. Since it is a square wave with a 50% duty cycle, the Darlington tube switch time is controlled by the switch signal generated by MSP430. In order to ensure sufficient light intensity, relatively high-power LED lights are selected for fill light. Therefore, these LED lights are powered by a 14 V power supply alone.

    Since the different light spectra will directly affect the efficiency of plant photosynthesis, the final ratio of red: blue LED is 5:1.
    In order to selectively supplement light for different external lighting environments, three groups of LED lamps are selected in the project. According to the external light intensity collected by the lighting module, the brightness and darkness of the three groups of LED lamps are selected. The specific circuit diagram is shown in Figure 4.

1.3 LCD display module The
    LCD model is 12864, which is controlled by a single-chip microcomputer to display the current external light intensity value and the number of lit LED lamps.

2 Project system software design
    This system uses C language to program the software part. The software part mainly includes the main function, timer interrupt program, and various subroutines.
    Timer A and timer B control the interrupt of the lighting module and the interrupt of the LED fill light module respectively. The specific block diagram is shown in Figure 5.

    

3. Results and analysis of the device experiment
    The control variable method was used for tomato seedlings, and the growth comparison in the sunny room is shown in Figure 6.
    In Figure 6, the plant on the left was continuously supplemented with light, and the plant on the right was intermittently supplemented with light at a duty cycle of 50%. The supplementary light point was set to the light saturation point of the tomato.
    No. 1 to 6 were photographed every 3 days after germination for 15 days. No pictures were taken for the control group without supplementary light. The experimental phenomena are as follows:
    (1) The growth of plants with 50% duty cycle supplementary light was better than that of plants with continuous supplementary light.
    (2) The growth of plants with supplementary light was significantly better than that of plants without supplementary light.
    It can be concluded that intermittent supplementary light can replace continuous supplementary light.
    Figure 7 is the comparison result of the same experiment on melon seedlings using the control variable method. No. 1 to 6 were photographed every 2 days after germination for 5 days. No pictures were taken for the control group without supplementary light. The experimental phenomena are the same as above.

    
    It can be concluded that intermittent fill light can replace continuous fill light.
    Cost accounting: To meet the fill light of 1 mx1 mx1 m space, the electricity fee is 0.6 yuan/kWh, and one month is calculated as 30 days. The power of each LED group is 1.5 W, and the continuous irradiation for 1 month consumes 1.08 kWh of electricity. 6 groups of lights are required, and the total electricity fee is 3.888 yuan. MSP430 microcontroller + ADC + LCD display costs 100 yuan in total, and the LED array group of 48 pieces/group × 6 groups costs 120 yuan in total. The chassis, switch, wire, PCB board, and bracket cost 50 yuan, totaling about 274 yuan. After mass production, the cost of each set of equipment can be reduced to less than 200 yuan, so the cost of the whole set of equipment is lower than that of traditional non-LED fill lights, and it also saves half of the electricity fee compared with ordinary LED fill lights. Longer use will save more expenses.

4 Conclusion
    This device uses 50% duty cycle intermittent light filling to save half of the electricity and improve photosynthesis efficiency; fills light to the light saturation point to save the part of electricity during transitional light filling; fills light with red and blue spectrum to avoid wasting energy with redundant spectrum; low cost and easy operation. It has good operability and application prospects.