Design of monitoring system for AVR modern facility agriculture

Facility agriculture is a production method that comprehensively utilizes advanced facilities and equipment and advanced production technologies to artificially create the best environmental conditions required for the growth and development of animals and plants, and through scientific and technical management, maximizes land output, resource utilization, labor productivity and product commodity rate, thereby obtaining the best economic, ecological and social benefits. Compared with traditional agriculture, it has outstanding advantages such as high space utilization and short production cycle, and has become a widely used crop production method at home and abroad. In response to the requirements of modern facility agriculture, a parameter acquisition system integrating temperature, humidity, CO2 concentration and light intensity is designed _, and combined with the relationship between crops and LED optical characteristics, a light source control system with adjustable LED spectrum is designed for supplementary lighting of crop environments. The monitoring system replaces the traditional manual monitoring method, and the degree of automation is greatly improved. According to the requirements of different crops, the system uses different spectra for supplementary lighting, which is more conducive to the growth of crops.

1. Monitoring system components

According to the needs of crop planting, a multi-parameter monitoring system suitable for modern facility agriculture is designed, which mainly includes the monitoring of parameters such as light, temperature and humidity and the spectrum adjustment function of LED light source. This system is used for crop lighting supplement. Different control LED spectrum ranges can be selected according to the characteristics of specific plants, thereby realizing flexible control of light sources. The system composition is shown in Figure 1.

Figure 1 System composition

1.1 Parameter measurement end

According to the four parameters that need to be collected and their characteristics, a parameter acquisition module is designed. The temperature measurement uses the DS18B20 temperature sensor, which uses a single bus interface. The temperature measurement range is between -10 degrees and +85 degrees. The temperature measurement accuracy is about ±0.5 degrees, which can meet the temperature accuracy requirements of the crop environment. The humidity parameter measurement uses the CHTM-02NA sensor, which outputs an analog voltage signal of 0-3V and a humidity measurement range of 10% - 95%RH. The _CO2 concentration measurement uses the MG811 sensor, which has a measurement range of 350-10000ppm and an output analog voltage of 30-50mV. The illumination measurement uses a photocell. A photocell is a photoelectric conversion device made using the photovoltaic effect, which detects the measured value by converting an optical signal into an electrical signal.

1.2 Controller Chip

Modern facility agriculture requires the simultaneous measurement of various parameters at multiple points in the greenhouse environment, so it has high requirements for the real-time performance and processing speed of the data. Therefore, the microprocessor uses MEGA128, which is an 8-bit low-power CMOS microprocessor based on the AVR RISC structure developed by ATMEL. Due to its advanced instruction set and single-cycle instruction execution time, the data throughput of MEGA128 is as high as 1MIPS/MHz, which can alleviate the contradiction between power consumption and processing speed in the system. It is a microcontroller with high cost performance and high stability, and the maximum operating frequency is 16MHz. MEGA128 minimizes system costs by expanding a complete series of general peripheral devices. It has SPI, JTAG and PWM timers, on-chip A/D converters, etc., which can meet the requirements of this design.

2 System Structure Design

According to different parameter monitoring requirements, the following functional modules are designed.

2.1 Parameter acquisition module

DS18B20 uses 1-Wire bus protocol, that is, bidirectional data transmission is realized on one data line. However, for MEGA128 microcontroller, the hardware does not support single bus protocol. Therefore, software must be used to simulate the protocol timing of single bus to complete the access to DS18B20 chip. And there are strict timing requirements for the data bits to be read and written. All timings are based on the host as the master device and the single bus device as the slave device. And each transmission of command and data starts from the host actively starting the write timing. If the single bus device is required to send back data, after the write command, the host needs to start the read timing to complete the data reception. The transmission of data and commands is low-order first. The temperature parameter acquisition module designed with DS18B20 is shown in Figure 2.

            Figure 2 Temperature acquisition module Figure 3 Humidity acquisition module

The humidity acquisition module uses a CHTM-02NA humidity sensor, which outputs an analog voltage signal of 0-3V and has a humidity measurement range of 10% - 95%RH. The analog voltage signal is converted into an analog digital signal through the PA0 port of the single-chip microcomputer MEGA128, as shown in Figure 3.

_The CO2 concentration acquisition module is shown in Figure 4. The external +6VDC voltage heats the HH end heating element. When its surface temperature is high enough, the MG811 element is equivalent to a battery, and its AB ends will output a voltage signal. The CO2 concentration can be measured based on the size of the voltage _signal .

            Figure 4 CO ₂ concentration acquisition module Figure 5 Illuminance acquisition module

In view of the advantages of LED in supplementary lighting for crops, a light acquisition system and a light control system with adjustable spectral range are developed, which can be conveniently applied to different types of plant supplementary lighting occasions. The illumination acquisition module is shown in Figure 5.

3 Conclusion

The purpose of system monitoring is to create suitable optimized environmental conditions such as light, temperature, humidity, and air for crop growth, and to adjust the crop growth process and maturity time to market in order to obtain better economic benefits. This paper designs a monitoring system that integrates multi-parameter acquisition with adjustable illumination and wavelength to facilitate remote monitoring and control of the crop environment, saving human capital while improving work efficiency. The system works reliably and meets the design requirements.