Design of cold chain logistics monitoring system

    At present, the China Food Industry Association points out that due to the lack or problems of cold chain logistics management, about 12 million tons of fruit and 130 million tons of vegetables are wasted every year, with a total value of more than 100 billion yuan. The Shanxi vaccine incident that shocked the whole country shows that the level of supervision is low, which directly affects food safety and medical safety. The formation of the cold chain logistics monitoring system will drive some corresponding industries, such as the quick-frozen industry and the vegetable industry, to a new level. This system is for the monitoring of cold chain logistics. The system includes terminal equipment and servers, and adopts GPRS data transmission, terminal low-power technology, and server data management to monitor the entire cold chain process in real time. After actual testing, the system meets the requirements of cold chain logistics management informatization and promotes the development of cold chain logistics and drug transportation.

1 System Design
    The system mainly monitors the whole process of cold chain in real time. It needs to collect and process information such as temperature, humidity, light intensity and geographical location, and transmit data to the server wirelessly through GPRS data packets. The system design integrates various factors to improve the response speed to sudden changes in the environment. The server side is designed in B/S mode, which monitors the status of items in real time through the Internet or mobile phone, so that users can check the environmental parameters of items in transit anytime and anywhere to reduce economic losses. As shown in Figure 1, it is a block diagram of the system, including terminal equipment, Internet, and B/S architecture server.

1.1 Terminal Hardware Design
    The terminal hardware part of the system is designed with MSP430 as the core, collects and processes the environmental characteristic data of the cold chain, and accesses the Internet server through the GPRS data packet function of SIM300. The terminal circuit includes a battery management part, a box switch status monitoring sensor, a working position monitoring sensor, a temperature sensor, a light sensor, and a humidity sensor. The terminal hardware block diagram is shown in Figure 2.

1.1.1 Hardware circuit design
    The design uses the MSP430F149 chip of TI Company of the United States as the control core, and controls the data transmission of the GPRS module through the serial port; uses its internal integrated A/D module to detect humidity; uses its 60 kB Flash memory to store a large amount of data to ensure the reliable preservation of data during the entire transportation process; and uses its internal analog comparator to detect the external light intensity. The system design uses the battery management circuit centered on the CN3063 battery charging management chip, provides a charging status indication, and provides a battery temperature protection circuit. The low-power LDO voltage regulator chip TLV70033 is used to provide 3.3 V power supply, as
shown in Figure 3. The system uses a photoresistor as a light intensity detection sensor to detect a certain intensity of light, as shown in Figure 4. CA0 and CA1 are the positive and negative input terminals of the analog comparator inside the microcontroller. Adjusting W1 can adjust the detection light intensity threshold. The DS18B20 is used to measure the ambient temperature, which has high stability and accuracy in stable measurement. The circuit design also uses the Hall switch TP4913 to detect the working position and working status. Through the Hall switch, the overall packaging of the product is simpler and the cost is lower.

1.1.2 Hardware low power design
    The system hardware power consumption requirements are strict, and the average power consumption of the system must be guaranteed to be <4.2 mW. Therefore, the MCU adopts low power technology, its active mode is 280μA@1 MHz, and the standby current is <1μA; the sleep current of the battery management chip is <3μA; SIM300 is selected to provide GPRS packet data transmission, and its standby current is <1 mA. [page] The
    low power consumption strategy of the hardware system is mainly concentrated in the following parts: the MCU operating frequency is 2 MHz; the operating voltage is 2.7 V, and all unnecessary resources are turned off; SIM300 supports software shutdown, startup, and command standby functions, providing an effective low power consumption method for the system; in order to reduce the static power consumption of the sensor part, the current limiting resistor method is used to reduce its static power consumption without affecting its accuracy, as shown in Figure 4, with a series resistor R24; low static power consumption and high efficiency LDO power management chip are selected to ensure that the power consumption is as low as possible and the power ripple is as small as possible.
The above overall low power consumption design and chip selection of the hardware make the static current consumption of the hardware system <200μA.
1.2 Software Design
1.2.1 Overall Software Design
    The system monitors the status of the entire cold chain transportation process in real time. The system detects cold chain environmental parameters, geographic location and detects dangerous information through terminal devices. It connects to the Internet server through UDP to send status data and receive terminal device working parameters. The cold chain item manager is presented in the form of a web page. Users can view and manage the item status in real time through a remote computer or mobile phone, as shown in Figure 5.

1.2.2 Terminal software design
    The terminal software design mainly includes sensor status detection, GPRS data packet link control, data backup, remote control, low power control, etc. Sensor status detection is processed by external interrupts. The microcontroller detects the status of each sensor through IO port changes, reducing system power consumption and shortening response time. The GPRS data packet link is connected to the server in UDP mode, which is a mature technology of SIM300. In addition, SIM300 also provides geographic location information, real-time time, and battery power, which can be obtained through AT commands; by analyzing the data packets returned by UDP, the terminal device can obtain information such as flight mode start and end time, data transmission interval, data collection cycle, data storage depth, temperature alarm upper and lower limits, time synchronization, etc. Data backup, store the collected important information in Flash for backup, use data compression processing, so that the microcontroller can store data depth of more than 7 days, and the entire storage space is recorded by loop overwriting, ensuring Flash read and write balance. The terminal software integrates effective low-power software design ideas. The terminal system monitors the working position through the Hall switch. When leaving the working position, the entire system is completely shut down and is at the microampere level of power consumption.
1.2.3 Server software design
    The terminal system exchanges data with the server via UDP. The server software starts a Socket listening process, receives valid packet data according to the custom data protocol, and saves it to the local database. The data packet includes the frame header, data length, data, and check bit. All data uploaded by the terminal is managed through unique ID information. On the existing PHP platform of the server, a web page for viewing and managing terminal data is run. The web page provides a platform for users to manage terminals. Users can view the status of items in the entire cold chain process to ensure the safety of items. As shown in Table 1.

2 System Test
    During the productization process of the cold chain goods monitoring system, the product's appearance and performance were comprehensively considered to overcome the difficulties of installation and harsh environment. The system's low-power design completed the 7-day cold chain monitoring task under the condition of limited battery power, meeting the working time requirements of the cold chain. The internal Flash can back up 7 days of data to ensure that the system can be in aviation mode for a long time without losing data. Through the website, the current status and location of the item can be viewed anytime and anywhere, and the working parameters of the terminal can be configured. According to the GPRS base station database provided by the mobile, the effective GPS coordinates of the base station can be obtained, and the movement trajectory of the item and the corresponding item status can be displayed on the map.

3 Conclusion
    The system design adopts the single-chip hardware low-power technology and software low-power management technology, and low-power GPRS data packet transmission technology, so that the terminal's working time meets the requirements. The system uses mature server data management technology and Web page technology to make cold chain management efficient and reliable. After testing, the system is stable and reliable, meets the requirements of the cold chain, and performs well in the transportation process monitoring of cold chain items. It will be a trend to apply this Internet of Things technology to logistics management, and it has a wide range of industrial needs.