The invention relates to a high-precision wireless monitoring system for atmospheric pressure and temperature
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With the development of science and technology, atmospheric pressure and temperature measurement in weather forecast, agricultural production, industrial sites and daily life and other fields are more and more widely used, people's atmospheric pressure and temperature measurement requirements are also increasing. In view of the current atmospheric pressure and temperature monitoring system measurement accuracy is not high, the production environment is bad, can not stay in the field for a long time [1⁃4], this paper proposes a high-precision wireless atmospheric pressure and temperature monitoring system. The system uses STC89C52 single chip microcomputer as the core control element, BMP180 sensor collects atmospheric pressure and temperature data, transmits information to the display through the radio frequency module, and gives alarm in special cases.
1 Hardware design of the system
1.1 Overall system design
The whole hardware of the monitoring system consists of data acquisition module, key control module, monitoring and display module, radio frequency transmission module and alarm module.
1) Data acquisition module: collect the data of temperature sensor and pressure sensor. The data acquisition module BMP180 is responsible for monitoring the environmental factor. When the status of the environmental factor is detected, it is sent to the monitoring and display module through RF communication.
2) Key control module: It is a common key switch device, because it is connected to the ground, when the key is pressed, through the software shake elimination program, it can correctly ground operation, real-time transmission of low-level signals to the MCU, so as to achieve the pressure and temperature threshold setting operation.
3) Monitoring display module: specially display the data collected by the sensor.
4) RF transmission module: Through wireless transmission, transmit the data transmitted by the transmitting end to the receiving end.
5) Alarm module: The use of two different colors of LED bulbs as alarm equipment, BMP180 sensor collected pressure or temperature data through the RF module transmission, the receiving end after the successful reception of the MCU data processing, when the pressure and temperature data do not meet the requirements of the threshold, the LED light will be flashed accordingly.
1.2 Main hardware selection
1.2.1 Selection of core processing chip
At present, there are two kinds of single-chip computers with low cost and simple programming, they are ATC51 series and STC52 series. ST89C52 microcontroller is superior to AT89C51 microcontroller in terms of performance, and the cost is lower, so this design uses STC89C52 microcontroller.
1.2.2 Selection of data acquisition sensor and communication module chip
Since the BMP180 sensor is convenient to use, can work at 3.3V and 5V voltage, and is more cost-effective than the MPX pressure sensor, this design uses the BMP180 sensor [5⁃6].
At present, there are many communication chips on the market, among which infrared communication is more popular in the past, and now the common radio frequency communication, because nRF2401 RF module than the infrared communication module transmission distance, and stability is better than the infrared communication module, so this design uses nRF2401 RF module.
1.3 Hardware design module
1.3.1 Data acquisition module
The core of the data acquisition module is the BMP180 pressure sensor module. After the data is collected by the module, it is processed by STC89C52 MCU and then handed over to the RF module for transmission. The connection between BMP sensor and MCU is shown in Figure 2 [7⁃10].
Figure 2 Connection diagram between BMP sensor and MCU
1.3.2 RF Communication Module
The module can easily adjust the transmit power and operating frequency through the SPI port bus, and the energy consumption is small because the working current is low. It is only 10.5 mA at -5 dBm operating power and 18 mA in receiving mode. This makes energy efficient design easier, allowing the nRF2401 to obtain two different channels of data at the same time under the same antenna. The connection between the RF module and MCU is shown in Figure 3.
Figure 3 Connection diagram between RF module and MCU
1.33 Key Control Module
Under the software program, the SCM can accurately judge whether the key is pressed, so as to achieve the function of modifying the pressure threshold and temperature threshold. The key control circuit is shown in Figure.
2 Software design of the system
2.1 Send module program
The program of the sending module is relatively simple, the sending end only needs to read the data of the BMP180 sensor through the I2C bus, and then send it out through the RF module.
2.2 Receiving module program
After receiving the data, the RF module at the receiving end performs two operations on the data in the buffer of the RF module. Since the pressure data is of long type, one of them is split into two, one takes the whole and the other takes the rest, and the data is sent in two times, and the temperature data is added. In total, there are three sets of data at the data sending end.
3 Result Analysis
3.1 Analysis of physical test data
1) nRF2401 transmission distance test
The transmitting end transmits different data, and each group of transmitting data corresponds to a different transmission distance. It is necessary to see whether the receiving end receives successfully. The distance test results are shown in Table 1. The results show that the effective transmission distance is 10 m, and after analysis, it is found that there is a certain relationship with the power supply, in addition, the wall block will also cause the relative transmission distance is not too far.
Table 1 nRF2401 transmission distance test
2) BMP180 pressure data test
The standard altitude of Jingzhou in Hubei Province is 32.6m, which is used as the lowest height of the test in the calculation process, and the altitude is changed with the change of the test site. Based on 5 groups of data, the altitude changes by 32.6m, 36.6m, 40.6m, 44.6m and 48.6m. After testing, it is found that the higher the altitude, the pressure will decrease accordingly. The specific measurement data, error and the function diagram of the influence of altitude factors on pressure are shown in Table 2 and Figure 7 respectively.
Table 2 Comparison of atmospheric pressure data of BMP180
Figure 7. Relationship between altitude and pressure function
3) Pressure and temperature comparison test
Since the altitude does not change much in the actual process, the temperature does not change much, and the atmospheric pressure data of different locations can be tested at a certain altitude. In the test process, the air pressure does not completely increase with the increase of temperature, but through the function image analysis, it can be roughly shown that temperature will affect the air pressure. The corresponding relationship between pressure and temperature data is shown in Table 3, and the corresponding functional relationship diagram is shown in Figure 8.
Table 3 Comparison test table of pressure and temperature at an altitude of 40.6m
Figure 8. Function diagram of pressure and temperature at an altitude of 40.6m
LCD1602 shows that the maximum alarm threshold of PH atmospheric pressure is 98 kPa, but the measured pressure value is 102.17 kPa, which obviously exceeds the maximum threshold, so the blue LED bulb flashes at this time.
Figure 9 Abnormal pressure alarm
4 Conclusion
The system can conduct real-time wireless monitoring and alarm for atmospheric pressure and temperature, the maximum wireless transmission distance is 10 m, the relative accuracy of atmospheric pressure test is ±0.01 kPa, and the average relative error is about 0.008%. When the actual atmospheric pressure and temperature exceed the set maximum threshold or lower than the set minimum threshold, real-time alarm can be carried out. The data test results show that in addition to the altitude factor can affect the atmospheric pressure, the temperature factor will also affect the atmospheric pressure. The experimental results show that the system has the advantages of high measurement accuracy and convenient use.
reference
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