【正文】 c, give a mand, singlechip microcontroller foot output level, triode conduction, fans, electric circuit, which began to turn it down. The design of the software system 中原工學(xué)院信息商務(wù)學(xué)院外文 翻譯 17 This system USES AT89C51 devices as the core, with DSl8B20 after the collected data, and the temperature inside the data storage AT89C51 deposit, LCD display, and pared with the prior value, and then the output signal by MCU control circuit and alarm circuit fan. Multifunctional temperature testing system software mainly include: function declarations, time delay function and DS18B20 initialization function, read the temperature, temperature DS18B20 data into a liquid crystal display characters such programs. Summary With the continuous development of industry of temperature measurement, the higher requirement, and more and more wide measuring range, so are the requirements for temperature detection technology more and more is also high. DSl8B20 introduced new digital temperature sensor and AT89C51 SCM, LCD1602 LCD module for constructing the temperature testing system. The hardware circuit and main program and system design of each module subroutines. This system USES the DALLAS is the digital temperature sensor DS18B20, plus A/D can output the digital quantity, the temperature signal directly convert serial digital signal processing for microputer. Accordingly. This system has the hardware circuit structure is simple, high precision, and shows the result conversion clear stability, low cost and significant advantages. In temperature measurement, such as grain of intelligent building, central air conditioning of the occasion to temperature testing has good application prospects. 教師評(píng)語(yǔ) 教師簽名： 20 年 月 日 。 c, Fahrenheit temperature range from 67 to + 257, incremental value . (6) support multipoint work function. Multiple DS1820 can pick on the same bus and, more temperature measurement. (7) 9 temperature resolution. Measuring results in nine serial transmission way the digital quantity. (8) user can set temperature alarm threshold. (9) have super temperature search function. ① .DSl8B20 principle of work The internal structure of DS18B20 DSl8B20 temperature measurement principle diagram shown in figure . Low temperature coefficient graph oscillation frequency vibration product temperature is used to produce with fixed frequency, pulse signal to counter l. High temperature coefficient crystals temperaturedependent its oscillation frequency change significantly. The signal generated as the counter 2 input pulses. Counter 1, 2 and temperature registers are counter in 55 degrees preset corresponding a base value. Counter l to low temperature coefficient of the pulse signal generated crystals, when the counter for subtraction counting the preset value reduced to 1, when the temperature counter O value will add l, counter the preset value will be l man again, to counter the l start low temperature coefficient of crystal oscillator pulse signal, so cycle count until the counter 2, stop counting to O accumulative temperature, temperature of the register for the register is measured values. Figure accumulative used for the slope pensation and fixed temperature measurement, the output of the process of nonlinear correction is less than the preset value counter l. ② .AT89C51 interface mode and DS18B20 Chip DS18B20 and the connection has two kinds: namely parasitic power and external power supply mode. Parasitic power way: in the parasitic power supply mode, the signal from the single chip DS18B20 in line drawing energy during the high level in the DQ energy stored in the internal capacitance, low level in signal in the energy consumed during the capacitance on working 中原工學(xué)院信息商務(wù)學(xué)院外文 翻譯 16 until highlevel ing again to parasitic power (battery). Parasitic power mode has three advantages: 1) distance measuring temperature, without the local power supply. 2) no conventional power in the condition reads the ROM. 3) circuit, with only one more concise root I/O realize temperature measurement. Want to make precise temperature conversion chip DS18B20, I/O line must ensure that the temperature conversion period, due to provide enough energy conversion in temperature during each DS18B20, when the current 1mA to work a few temperature sensor in the same root hanging on the I/O multipoint temperature measurement, only by K and resistance will not be able to provide enough energy, which cannot be switchover temperature or errors. The external power source supply way: in the external power supply modes, DS18B20 work power by VDD pin, I/O access line does not need strong pull up, there is no shortage of electricity power, can ensure accuracy and conversion in the bus theory can be articulated multiple sensor DS18B20, multipoint temperature measuring system. This system USES the external power source. Connection method is one foot grounding and DS18B20 2 feet (DQ) and AT89C51 foot an I/O port, 3 feet line up + 5V. A89S52 in the I/O port and + 5V connection between a K pullup resistors, to ensure the normal operation of the data collection. If you want to test system, posed multipoint temperature in the same root chip I/O port in the same line, and the method of connecting the parallel more pieces of DS18B20 chip. （ 3） LCD1602 LCD 1602 LCD module can and monolithic integrated circuit AT89C51 directly interface. （ 4） Buzzer driver circuit Due to the working current buzzer is pared monly big, so I/O microcontroller is not directly driven by amplifying circuit, so it is generally used to dri