1 System hardware design
The system structure is shown in Figure 1. The 51 series single-chip microcomputers AT89C55 and AT89C51 produced by ATMEL are used as the core, of which the host uses AT89C55 and the slave uses AT89C51. The slave is responsible for 64-point data detection. The temperature and humidity of each detection point are converted into voltage signals through temperature and humidity sensors and their conversion circuits; the signal is selected through the matrix network, and the obtained signal is sent to the corresponding signal amplification and sorting circuit for amplification, and then enters the A/D converter for analog-to-digital conversion, and the digital quantity is sent to the slave, and then processed by the slave, sent to the LED for display, and transmitted to the host AT89C55 at regular intervals; the host is responsible for collecting data in each granary (50~100 granaries can be monitored), realizing data storage, printing and calling historical data, and can display the timely temperature, humidity and alarm status of each granary on a roving basis.
AT89C55/51 chip is a 51 series 8-bit single-chip microcomputer launched by ATMEL. The AT89C55 chip mainly has 20KB Flash memory, 256 bytes of on-chip RAM, 4 8-bit bidirectional addressable I/O ports, 1 full-duplex UART (universal asynchronous receiver transmitter) serial interface, 3 16-bit timers/counters, multiple priority nested interrupt structures, and an on-chip oscillator and clock circuit.
In this system, the host uses the rich 20KB flash memory resources of AT89C55 to permanently save real-time measurement information, historical measurement data and other key results, and the slave completes data collection and transmission. The host is located in the monitoring room, and the slave is located in each granary. There is a certain distance between the master and the slave. The signal transmission adopts serial asynchronous communication. The UART module integrated in the AT89C55/51 single-chip microcomputer is suitable for communicating with other computer systems and external peripheral chips of the single-chip microcomputer, and can realize three working modes: full-duplex asynchronous, half-duplex synchronous master control and half-duplex synchronous slave control. In this system, the UART module is used to work in full-duplex asynchronous communication mode, where TX is the transmit line and RC is the receive line. RS-422 drivers and receivers, such as MC3487 and MC3486 chips, are used to achieve stable signal transmission.
The system structure is shown in Figure 1. The 51 series single-chip microcomputers AT89C55 and AT89C51 produced by ATMEL are used as the core, of which the host uses AT89C55 and the slave uses AT89C51. The slave is responsible for 64-point data detection. The temperature and humidity of each detection point are converted into voltage signals through temperature and humidity sensors and their conversion circuits; the signal is selected through the matrix network, and the obtained signal is sent to the corresponding signal amplification and sorting circuit for amplification, and then enters the A/D converter for analog-to-digital conversion, and the digital quantity is sent to the slave, and then processed by the slave, sent to the LED for display, and transmitted to the host AT89C55 at regular intervals; the host is responsible for collecting data in each granary (50~100 granaries can be monitored), realizing data storage, printing and calling historical data, and can display the timely temperature, humidity and alarm status of each granary on a roving basis.
AT89C55/51 chip is a 51 series 8-bit single-chip microcomputer launched by ATMEL. The AT89C55 chip mainly has 20KB Flash memory, 256 bytes of on-chip RAM, 4 8-bit bidirectional addressable I/O ports, 1 full-duplex UART (universal asynchronous receiver transmitter) serial interface, 3 16-bit timers/counters, multiple priority nested interrupt structures, and an on-chip oscillator and clock circuit.
In this system, the host uses the rich 20KB flash memory resources of AT89C55 to permanently save real-time measurement information, historical measurement data and other key results, and the slave completes data collection and transmission. The host is located in the monitoring room, and the slave is located in each granary. There is a certain distance between the master and the slave. The signal transmission adopts serial asynchronous communication. The UART module integrated in the AT89C55/51 single-chip microcomputer is suitable for communicating with other computer systems and external peripheral chips of the single-chip microcomputer, and can realize three working modes: full-duplex asynchronous, half-duplex synchronous master control and half-duplex synchronous slave control. In this system, the UART module is used to work in full-duplex asynchronous communication mode, where TX is the transmit line and RC is the receive line. RS-422 drivers and receivers, such as MC3487 and MC3486 chips, are used to achieve stable signal transmission.
The measurement circuit is composed of sensors, matrix measurement networks, multi-channel analog switches and amplifier circuits. Temperature measurement range: -45～+45℃, ±0.5℃; humidity measurement range: 0～99％RH, ±0.8％RH. The temperature sensor uses the integrated temperature sensor AD590M, which has the characteristics of linear current output 1μA/K; temperature range -55～150℃; voltage input/current output; laser correction to ±0.5℃ calibration accuracy (AD590M), and linearity can reach ±0.3℃/FS. When in use, the AD590M can be inserted into the granary pile. In view of the humidity measurement range and accuracy requirements, the humidity sensor uses the humidity-sensitive integrated sensor IH-3602. This is a capacitive humidity sensor, which contains a conditioning circuit and a temperature compensation circuit, and outputs a DC voltage of 0.8～4V, which can be directly input into the A/D converter through a multi-way switch.
The matrix measurement network is composed of multi-way analog switches CD4051, CD4052, temperature sensor AD590, and humidity sensor IH-3602, and its connection is shown in Figure 2. The temperature (humidity) measurement matrix is composed of 8 analog switches of CD4051, 4 analog switches of CD4052 and 32 AD590 (32 IH-36021). The selection of each measuring element is controlled by the address code. In the matrix network composed of CD4051, CD4052, AD590, and IH-3602, the 4 input lines A and B of the two CD4052 and the 3 input lines A, B, and C of CD4051, a total of 7-bit address codes, are provided by the P0 port of AT89C51. The INH of CD4052 is directly connected to the high level, while the INH of CD4051 is provided by the P2 port. The temperature and humidity output signals, i.e., the OUT of CD4052, are respectively connected to the temperature and humidity amplifier circuits.
The matrix measurement network is composed of multi-way analog switches CD4051, CD4052, temperature sensor AD590, and humidity sensor IH-3602, and its connection is shown in Figure 2. The temperature (humidity) measurement matrix is composed of 8 analog switches of CD4051, 4 analog switches of CD4052 and 32 AD590 (32 IH-36021). The selection of each measuring element is controlled by the address code. In the matrix network composed of CD4051, CD4052, AD590, and IH-3602, the 4 input lines A and B of the two CD4052 and the 3 input lines A, B, and C of CD4051, a total of 7-bit address codes, are provided by the P0 port of AT89C51. The INH of CD4052 is directly connected to the high level, while the INH of CD4051 is provided by the P2 port. The temperature and humidity output signals, i.e., the OUT of CD4052, are respectively connected to the temperature and humidity amplifier circuits.
The software of the multi-channel temperature and humidity monitoring system is designed in a modular way, mainly including the host program and the slave program. The slave program design usually performs initialization first, such as setting interrupts, timers, serial ports, and initialization of external programmable devices, and then cyclically executes the main functions, such as timing, data acquisition, digital filtering, display, and timing data transmission to the host. The host receives the acquisition signal sent by the slave at a regular time, saves it and displays it in real time. The process is shown in Figure 3. After power-on reset, different granary position numbers, temperature and humidity values, and their measurement time are displayed, and the keyboard management program module and the receiving program module are called. In order to prevent the program from running away, the master and slave machines are respectively designed with watchdog circuits to ensure the normal operation of AT89C55 and AT89C51.
This design uses the AT89C51/55 single-chip microcomputer, which has reliable performance and simple circuits and is suitable for mass production. Moreover, the system can make full use of the unused software and hardware resources in the AT8951/55, making the system redevelopable.
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