Design of battery power temperature monitoring system for communication power supply
0 Introduction In the design and construction of communication systems, 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. A survey result of American APC Company shows that more than 75% of communication system failures are caused by power supply equipment failures. At present, the power supply of the communication system is mostly provided by the uninterrupted battery, and 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.
1 system composition The functional block diagram of the battery temperature monitoring system is shown in Figure 1. It is mainly composed of voltage, temperature and humidity collection, temperature collection, 89S51 single-chip microcomputer, keyboard control module, display circuit module, and communication module. The system can complete the temperature measurement of 6 or more groups of communication batteries, the environmental measurement of 1 computer room (temperature and humidity measurement), the measurement of 2 DC voltages and 2 AC voltages, and the transmission data distance is more than 200 m.
2 Hardware design
2. One-chip computer choice The one-chip computer of this system chooses 89S51, this one-chip computer adopts 0.35 new craft. The cost is reduced and the function is improved. Compared with the traditional 89C51 microcontroller, it has the following characteristics:
(1) The functions are increased, the performance has been greatly improved, and the price is basically unchanged;
(2) ISP online programming function;
(3) The maximum operating frequency is 33 MHz, and the calculation speed is faster;
(4) With duplex UART serial channel;
(5) Internally integrated watchdog timer;
(6) Double data indicator;
(7) Strong compatibility, fully compatible with all 51 sub-series products.
2.2 The choice of temperature sensor and its connection with the single-chip microcomputer DS18B20 temperature acquisition, DS18B20 has a unique single bus interface mode, through the serial communication interface (I / O) directly output the measured temperature value interface mode, CPU only needs one The root port line can realize two-way communication with DS18820; no external components are required in use; it contains a parasitic power supply, which can be either a parasitic power supply or a VDD direct power supply; the allowed voltage range is 3.0 to 5.5 V, The operating current during temperature / digital conversion is about 1.5 mA, the standby current is only 1 μA, and the typical power consumption is 5 mW; the temperature measurement range is -55 to 125 ° C, and the error is less than 0 between 0 and 85 ° C ．5 ℃; support multi-point networking function, multiple DS18B20 can be connected to a bus, which can realize multi-point temperature measurement; with negative pressure characteristics, when the polarity of the power supply is reversed, the thermometer will not burn due to heat , But it doesn't work.
The connection between DS18B20 and the single-chip microcomputer is shown in Figure 2. It is directly powered by VCC, connected with a pull-up resistor of about 4.7 kΩ, and DQ is directly connected to P1.0 port of the single-chip microcomputer.
The access flow of the CPU to the DS18B20 is to initialize the DS18B20, that is, the ROM operation command, and the memory (including the pad RAM and E2PROM) operation command, that is, data processing. All processing on the single bus begins with initialization, and the initialization sequence consists of the reset pulse sent by the master and the response pulse sent by one or more slaves. After the master receives the response pulse from the slave, it indicates that there is a single bus device online, the master can start the ROM command and memory operation command to the slave, so that the DS18B20 can complete the temperature measurement and store the measurement result in the high-speed temporary memory, and then read This result.
2.3 Measurement of AC, DC voltage and temperature and humidity of the computer room TLC1543 is selected for the measurement of DC voltage, AC voltage and the temperature and humidity of the computer room. TLC1543 is a 10-bit 11-channel A / D converter. The connection with the single chip is shown in Figure 3. The environment measurement (temperature, humidity) of the computer room adopts JWS temperature and humidity transmitter, and the output signal is a standard 0 ~ 5 V DC voltage signal; the data collection of DC voltage is directly sent to the A / D converter after the resistance is divided, and the AC voltage The collection is also sent directly to the A / D converter after being divided and rectified.
2.4 Display circuit design The temperature display uses 6-bit LED, and the connection with the single chip is shown in Figure 4. The display module is composed of 8279 keyboard, display interface chip and corresponding driving circuit. During the scanning process of 8279 scanning lines SLA ～ SLC, the content of the internal display unit of the chip can be sent to the output data lines OA0 ～ OA3 and OB0 ～ OB3 scanning lines to be decoded by 74HC138, as the bit selection line of multi-bit LED digital tube. After reversed by 74LS04, it passes through the bit driver chip, which is used to drive different nixie tubes. At the same time, the data sent from OA0 to OA3 and OB0 to OB3 are used to correspondingly drive the eight display segments of each nixie tube, and the six nixie tubes are driven to emit light in turn. The driving chip adopts SN75491 and SN75492 to drive the segment and bit display of the nixie tube respectively to ensure the maximum current required when all 6 nixie tubes are lit.
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