Monitoring method of battery temperature of communication power supply

Communication power battery temperature monitoring solution

The communication power supply is called the heart of the communication system. The power supply system will directly affect the reliability and stability of the communication system. At present, the power supply of the communication system is mostly provided by uninterrupted batteries. The high temperature of the battery will inevitably affect the working efficiency and life of the battery. Therefore, it is of practical significance to monitor the working temperature of the battery in real time. A survey result of APC in the United States shows that more than 75% of the communication system failures are caused by power supply equipment failures.

Topic content:

System composition of battery temperature monitoring system
Software and hardware design of battery temperature monitoring system
Solution:

Voltage, temperature and humidity acquisition, temperature acquisition
Communication between modules
Data display

System composition

The principle block diagram of the battery temperature monitoring system is shown in Figure 1. It is mainly composed of voltage, temperature and humidity acquisition, temperature acquisition, 89S51 single-chip microcomputer, keyboard control module, display circuit module, and communication module. The system can complete the temperature measurement of 6 or more communication batteries, 1-way machine room environment measurement (temperature and humidity measurement), 2-way DC voltage and 2-way AC voltage measurement, and the data transmission distance is greater than 200m.

Hardware Design

1 MCU selection

The system uses 89S51 microcontroller, which adopts the new 0.35 process. The cost is reduced and the function is improved. Compared with the traditional 89C51 microcontroller, it has the following characteristics:
(1) More functions, greatly improved performance, and basically unchanged price;
(2) ISP online programming function;
(3) The maximum operating frequency is 33MHz, and the calculation speed is faster;
(4) It has a duplex UART serial channel;
(5) Internal integrated watchdog timer;
(6) Dual data indicators;
(7) Strong compatibility, fully compatible with all 51 sub-series products.

2. Selection of temperature sensor and its connection with microcontroller

DS18B20 is used for temperature acquisition. DS18B20 has a unique single bus interface mode. It directly outputs the measured temperature value interface through the serial communication interface (I/O). The CPU only needs one port line to realize two-way communication with DS18820. It does not require any peripheral components during use. It contains a parasitic power supply, which can be powered by either parasitic power supply or VDD directly. The allowable voltage range is 3.0~5.5V, the working current during temperature/digital conversion is about 1.5mA, the standby current is only 1μA, and the typical power consumption is 5mW. The temperature measurement range is -55~125℃, and the error is less than 0.5℃ between 0~85℃. It supports multi-point networking function, and multiple DS18B20 can be connected to one bus to realize multi-point temperature measurement. It has negative pressure characteristics. When the power polarity is reversed, the thermometer will not burn due to heat, but it cannot work normally.
The connection between DS18B20 and the microcontroller is shown in Figure 2. It is powered directly by VCC, connected to a pull-up resistor of about 4.7kΩ, and DQ is directly connected to the P1.0 port of the microcontroller.

The CPU's access process to DS18B20 is: initialization of DS18B20, i.e., ROM operation command, memory (including scratchpad RAM and E2PROM) operation command, i.e., data processing. All processing on the single bus starts with initialization. The initialization sequence consists of a reset pulse from the host and a response pulse from one or more slaves. After the host receives the response pulse from the slave, it indicates that a single bus device is online. The host can then start to issue ROM commands and memory operation commands to the slave, allowing DS18B20 to complete the temperature measurement and store the measurement results in a high-speed temporary memory, and then read out the results.
3 Measurement of AC and DC voltages and room temperature and humidity

TLC1543 is used to measure DC voltage, AC voltage and room temperature and humidity. TLC1543 is a 10-bit 11-channel A/D converter, and its connection with the microcontroller is shown in Figure 3. JWS temperature and humidity transmitter is used to measure room environment (temperature and humidity), and the output signal is a standard 0-5V DC voltage signal; the DC voltage data is directly sent to the A/D converter after resistor voltage division, and the AC voltage data is also directly sent to the A/D converter after voltage division and rectification.

4 Display circuit design

The temperature display uses 6-bit LEDs, and the connection with the single-chip microcomputer is shown in Figure 4. The display module consists of an 8279 keyboard, a display interface chip, and a corresponding drive circuit. During the scanning process, the 8279 scan lines SLA~SLC can send the content of the internal display unit of the chip to the output data lines OA0~OA3 and OB0~OB3. The scan lines are decoded by 74HC138 and used as the bit selection lines of the multi-bit LED digital tubes. After being inverted by 74LS04, they are passed through the bit driver chip to drive different digital tubes. At the same time, the data sent by OA0~OA3 and OB0~OB3 are used to drive the 8 display segments of each digital tube accordingly, so that the 6 digital tubes are driven to emit light in turn. The driver chips use SN75491 and SN75492 to drive the segment and bit display of the digital tubes respectively, ensuring the maximum current required when all 6 digital tubes are lit.

5. Communication module design

In order to meet the data transmission distance of more than 200m, the communication uses the 75LBC180 full-duplex 485 chip, and the conversion between the microcontroller communication level and the computer level is completed by MAX232, as shown in Figure 5. The MAX232 chip is an interface circuit designed for the RS232 standard serial port of the computer and is powered by a +5V single power supply. In addition, the conversion from RS232 to RS485 can use a dedicated converter, such as BOK-60 or ATC-160A passive converter.

Software Design

The software design of the battery temperature monitoring system mainly includes the main program, external interrupt subroutine, display subroutine, etc. Figure 6 is the main program flow chart of the system. It is used to complete the functions of calling DS18B20, interrupt management, calculation of measured temperature value and display of temperature value. The host 89S51 first resets the pulse to reset all DS18B20 chips on the signal line, then sends the skip ROM operation command to activate all DS18B20 online, and then the system switches to the interrupt processing flow to complete the temperature conversion and reading. The external interrupt subroutine completes the reading of the temperature measurement data, and the display subroutine completes the initialization of the LCD and displays the temperature value.

The communication power supply battery temperature monitoring system based on 89S51 and DS18B20 has a simple interface, occupies fewer ports of the microprocessor, and can save a large number of leads and logic circuits. Compared with traditional devices, it has the advantages of simple structure, low cost, high reliability and temperature measurement accuracy, low power consumption, and wide application.