发布时间 : 星期三 文章基于IA4421分布式温度和湿度采集系统(英语原文与翻译)更新完毕开始阅读34ddfb12185f312b3169a45177232f60dccce7d4
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Distributed Temperature and Humidity Acquisition System Based
on IA4421
Abstract-Nursery sheds have the characteristics of staying closely, quantity,
parameter changing slowly, a small amount of data, so the article presents a distributed centralized monitoring system based on a short-range radio transceiver IA4421 chip.The front-end system circuit choose single-chip STC89LE52RC as the control of the core, complete a humidity sensor HSl101, the temperature sensor DS18B20 circuit and IA4421 peripheral circuit design, method of CRC, after completing front-end systems and hardware design of data center ,design gives the software design , the corresponding flow chart and some instances.
Keywords-IA4421; DS18B20; HSllOl; CRC; wireless transmission; distributed I. INTRODUCTION
The short-range wireless transmission technology can get more than one nursery shed parameters of temperature and humidity and pooled centralized monitoring , this type of scene temperature and humidity parameters changes slowly , it takes more interval time in data acquisition, and the amount of data value for each sample is small ; from a technical perspective ,with the monitoring system of this type with many monitoring points ,it is more suitable to use the advanced zigbee wireless network . However, examine from an economic point of view, such programs are too much expensive. In this paper a program came up with a distributed centralized monitoring based on the wireless chip IA4421, the program is suitable for the above-mentioned type of scene, and it has obvious advantages in cost .
II. SYSTEM AND HARDWARE DESIGN
A. System components
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With too many distributed multi- monitoring points which the distance is short ( d < 100m ) and distribution, system decide to adopt a short-range wireless communication chip to form a distributed wireless monitoring system , shown in Figure 1 .There are m front-end monitors and a wireless monitoring system center, each front-end monitor has a microcontroller core, collected by the temperature and humidity sensors to get temperature and humidity parameters , the microcontroller send the parameters to the wireless monitoring center through front-end wireless communications chips.
Figure 1. Distributed wireless acquisition system
Wireless monitoring center is the center of the whole system, it has taken to the polling work, and give instructions which were issued to the various front-end monitoring units , the front-end monitoring units only received its own polling command and then decided to launch out of the unit data. The system is designed every 3 seconds polling program , every minute can be polled to 20 monitoring units and it is better to extend the polling cycle or decrease the pollmg interval to solve the larger-scale monitoring site . B. Front-end monitoring units
Front-end monitoring unit is responsible for the collection site
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of the temperature and humidity parameters , and send the collected to the wireless monitoring center , the circuit schematic shown in Figure 2. Design uses STC89LE52RC as the controller core , the controller has the advantage of downloading the program through serial port. The instructions and the codes are fully compatible with the 51 MCU within six interrupt sources , four mterrupt priority levels , a watchdog timer (WDT), the clock frequency up to 40MHz [1] . The system is supplied with DC6V, using 3.3V voltage regulator chip ASM1117 -3.3 to supply microcontroller and wireless chip.
Dallas company's I-Wire bus digital temperature sensor DS 18B20 is used in temperature measurement circuit. The design uses a 3-pin TO-92 small-size package , the temperature measurement range of -55 to 125°C , programmable for 9-12 bit A/D conversion and the precision temperature resolution up to 0.0625 ° C , The digital format of temperature with converted of 12 bit takes the maximum time of 750 ms [2] . The design uses 9 bit digital format, the default conversion accuracy is 0.5 ° C , the conversion time is about 100ms[3].
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Figure 2. Circuit of front-end monitoring units
Humidity acquisition uses humidity sensor HS1101 and NE555 in the circuit,HS1101 can affect the oscillation frequency of the NE555 circuit when the outside humidity changes and the capacitor value of both end of the HS1101 is changed , thereby changing the output frequency of the timing circuit. The MCU system calculate the humidity field through the measurement of the frequency of its output . The site humidity and the output frequency corresponding relationship[4] is shown in Table1.
TABLEI HUMIDITY AND THE OUTPUT FREQUENCY CORRESPONDING RELATIONSHIP RF Fr 10 7224 20 7100 30 6976 40 6853 50 6728 60 6600 70 6468 80 6330 90 6186 C. Wireless transceiver portion and the wireless monitoring center circuit Integration Associates production of short-range wireless transceiver chip IA4421 is used in this design. This is a fully integrated , low power consumption and requires very few external components, multi-channel , programmable , low-cost , high-performance wireless communications chip [5] .
Chip has a programmable PLL frequency synthesizer with high-precision, and the sending letter frequency offset and receiver bandwidth is also programmable, it has great flexibility in applications. The chip uses FSK modulation mode, the operating band is optional for the 433M, 868M and 915M , the largest sending letter power up to 8dBm, when the receiver sensitivity is -109dBm and the bit error rate is 10-3 , the air rate up to 115.2kbpS,sending letter current less than 24mA , receiving current is less than 10mA . standby current is only 0.3uA the maximum communication distance is 100 meters to 200 meters [6] . In addition to the crystal oscillator and the antenna the IA4421 peripheral circuit has only two inductors and two capacitors , and their specific parameters depend on the system of communication frequency
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