Design of Mobile Monitor for Greenhouse

With the development of science and technology, my country's agricultural development has also achieved good results. Everything has its two sides, and many problems have been highlighted while making progress. The first problem is: my country is a populous country with abundant natural resources, but the per capita share is small; the second problem is that my country's agricultural production has low technological content and high production costs. Generally, family production has not formed large-scale production. 

1. Current status of greenhouse technology at home and abroad

China can be regarded as the earliest country with greenhouse technology. Most greenhouses use thin-film technology, which is easily affected by the environment. At the end of the 20th century, my country introduced a series of modern greenhouse systems from Europe, America, Japan and other countries: heating system, wet curtain cooling system, irrigation system, monitoring and centralized control system, etc. for research. In March, my country's first single-well pumping and irrigation shallow ground energy greenhouse environment control system was completed in the Chinese Academy of Agricultural Sciences.

The Netherlands is the country with the most developed greenhouse production in the world. Its greenhouses are mainly made of glass and cover a wide area, ranking among the top in the world. According to the characteristics of the natural environment and the computer control and management system developed by the United States, the environmental factors such as soil water content, temperature, air humidity, fertilizer, and carbon dioxide concentration in the greenhouse are automatically regulated. Japan is the country with the largest fruit tree cultivation area and leading planting technology in the world. The computer control system developed by it can automatically detect changes in environmental factors and then make appropriate adjustments; it can also clean, screen, pack, and Fresh-keeping and other operations are fully automated.

2. The structure and working principle of the intelligent greenhouse system

The system frame is shown in Figure 1. First, set the upper and lower limits of temperature, humidity and light intensity by writing codes through the single-chip microcomputer, and then press the corresponding number on the remote control to move the car. After arriving at the designated place, the temperature and humidity sensor and the photoresistor sensor start to collect data, and send the collected data to the single-chip microcomputer through analog-to-digital conversion, and the single-chip microcomputer processes and transmits the data to the display screen and displays it. When the single-chip microcomputer detects that the data value exceeds the set value, it will drive the buzzer to alarm.

1. Selection of MCU

The history of single-chip microcomputer development can be divided into three stages: (1) In the initial stage, because the process technology is still relatively elementary, the single-chip microcomputer adopts a dual-chip form and its functions are relatively simple, such as the F8 single-chip microcomputer produced by Fairchild. (2) Low-performance microcontroller stage. There are 8-bit CPU, parallel I/O port, 8-bit timing counter, RAM and ROM integrated in the single-chip microcomputer, but there is no serial port, and the interruption is simple. (3) High-performance single-chip microcomputer stage. Low cost, high performance, simple operation, and multiple models to meet different needs. With the development of economy and society, people's demand for microcontrollers is also increasing, and the application of single-chip microcomputers has penetrated into various fields of people's lives, such as the control of various instruments, information communication, real-time data acquisition, etc., which also stimulates In order to improve the production of single-chip microcomputers in the market, the competition of various manufacturers is becoming more and more fierce, which is conducive to the improvement of the production process and performance of single-chip microcomputers.

2. LCD12864 liquid crystal module

The liquid crystal display has the advantages of small size, low power consumption, simple operation and low cost. There are also many types of display screens, including character type, dot matrix type, etc., and the commonly used one is dot matrix type. The display screen on most single-chip microcomputer development boards is LCD1602, and the display range is too small to meet the requirements for real-time display of data such as temperature, humidity, and light intensity. Therefore, LCD12864 is selected to meet such requirements. LCD12864 is an 8-bit/4-bit parallel, 3-wire or 2-wire serial interface; its display resolution is 128×64, 128 16×8-dot ASCII character sets, built-in 8 192 16×16-dot Chinese characters . The interface mode of the module is highly operable and flexible, and it is convenient to execute instructions, and the graphical interface can be exchanged in Chinese.

3. Sound and light alarm circuit

When the single-chip microcomputer system detects that the ambient temperature and humidity are higher or lower than a certain set value, the single-chip microcomputer sends a signal to drive the indicator light to light up, and the buzzer sounds an alarm at the same time. When the temperature and humidity are within the normal range, the sound and light alarm is released.

4. Intelligent remote control car design

(1) General idea: The intelligent remote control car consists of two main parts: the infrared remote control part and the intelligent control part. The infrared remote control part uses a modular remote control keyboard as the transmitter, and the integrated HX1838 as the receiver; the intelligent part uses the STC89C52 single-chip microcomputer as the general control center, and uses the L293D motor drive module to control the DC motor, and then control the turning, start and stop, and speed of the car speed.

(2) Infrared remote control module: Infrared remote control is divided into two parts: receiving and transmitting. The transmitting circuit sends the signal to the receiver through the keyboard and code modulation through infrared rays; because the signal is very weak, the receiver will amplify it after receiving the signal. After filtering out unnecessary signals and shaping, TTL-level encoded signals are obtained, and then sent to the single-chip microcomputer. After the single-chip microcomputer decodes, it sends out corresponding instructions to control the corresponding part of the operation. The infrared receiver adopts TL1838, which has 3 terminals: ground terminal, signal output terminal and power supply terminal.

(3) DC motor drive module: The output current of the single-chip microcomputer is too small, and the DC motor requires a large drive current, so the motor drive circuit is needed to cooperate with the single-chip microcomputer to make the motor run normally. L293D is a chip specially produced for the convenience of driving the motor. The input voltage of this module can reach 36V, the working voltage is 5V, the output current is ±600 mA, and it contains 4 control terminals and 4 output terminals. A is the input control terminal, Y is the output control terminal, 1A controls 1Y, 2A controls 2Y, 3A controls 3Y, 4A controls 4Y, when A=1, Y outputs 12 volts; when A=0, Y outputs 0V. The 1,2EN and 3,4EN enable ports need to be shorted, and the maximum working voltage of the chip is 7V.

5. Introduction of DHT22 temperature and humidity sensor

Temperature and humidity detection can use DS18B20 temperature sensor and HS1101 humidity sensor respectively, but the design circuit is complicated, so DHT22 is used as the temperature and humidity detection module. DHT22 is a single-chip intelligent digital composite sensor, which adopts special digital module acquisition technology and temperature and humidity sensing technology, so that the sensor has high reliability and long-term stability. It includes an energy gap temperature measuring element and a capacitive polymer humidity measuring element, and is closely connected with an 8-bit single-chip microcomputer. It has small size, wide measurement range and high cost performance. Can measure 0%~100%RH humidity, error ±2%RH, -40~80°C, error ±0.5°C.

6. Introduction of photoresistive sensor

A photosensitive sensor is a semiconductor device that converts light signals into electrical signals. It is actually equivalent to a PN junction. Compared with ordinary diodes, it is somewhat different in structure. In order to increase the area of incident light, the area of the PN junction is relatively large, and the electrode area It is relatively small, and needs a window in contact with light when it is used. When the light changes, the PN junction is automatically turned on or off. The light intensity detection is mainly measured by the photosensitive sensor module. The module is mainly composed of an LM393 voltage comparator and a photoresistor. This system uses a thin-chip photoresistor as a sensor, the incident light is enhanced, the resistance is reduced, the incident light is weakened, and the resistance is increased, and then the optical signal is converted into an electrical signal, and then converted into high and low levels by a voltage comparator and sent to the microcontroller.

3. Analysis of Greenhouse Environmental Test Results

As the temperature of the test environment rises, the temperature data displayed on the display also rises; the humidity fluctuates and is basically maintained at 45RH%, which is more in line with the indoor humidity at room temperature. One shortcoming is that the response speed of the display screen is a little slow. Under the comprehensive consideration of the laboratory environment, hardware, software and other conditions, the monitoring results can meet the needs of the design, but the software and hardware still need to be optimized. As the light intensity increases, the resistance of the photoresistor decreases, and the output voltage of the photosensitive module decreases. The data displayed on the display is consistent with the actual measured data, and there is a certain measurement error, which may be due to the shaking of the finger when measuring the voltage or the imperfect hardware circuit, resulting in poor contact. The temperature and humidity module test is shown in Figure 2.

Summarize

Due to the lack of laboratory conditions, knowledge, experience and time in this design, the monitor still needs to be improved in many places. Practice is the only criterion for testing the truth. Only by putting the monitor into production and continuously debugging can we understand the existence of the system. problem, and then solve the problem. With the development of the economy, our country pays more and more attention to the development of agricultural science and technology, and invests more and more in scientific research. Traditional agricultural production has low efficiency, is greatly affected by the environment, and consumes a lot of manpower and material resources. With the introduction of high-tech Agricultural planting, the future agricultural production will definitely move towards intensification, high yield, scale and high level.

The above is the hardware design example of the single-chip microcomputer-based greenhouse mobile monitor introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. If you have design requirements for smart greenhouses, you can trust us. We represent a variety of single-chip microcomputers, voice chips, dual-mode Bluetooth ICs, and wifi chips. Brands include Songhan MCU, Yingguang MCU, Jerry Bluetooth, Ankai Bluetooth, Allwinner, and Realtek. Our technical services include: PCB design, microcontroller development, Bluetooth solutions, software and hardware custom development, APP development, small program development, WeChat official account development, etc. It can also undertake the design of intelligent electronic products, the development of living appliances, the research and development of beauty equipment, the application of Internet of things platform, the smart home control system, the development of TWS earphones, Bluetooth earphone speakers, the development of children's educational toys, the design of electronic education products, etc.