At present, the internationally new temperature sensor is developing from analog to a digital form, from integrated to intelligent and networked. Intelligent temperature sensor DS18B20 integrates temperature sensors, A/D sensors, registers, and interface circuits in a chip. It has direct digital output, testing and control functions, long transmission distance, strong anti -interference capacity, miniaturization, micro -power Electric Filter Fan Cabinet Heater Fan Heater with Thermostat consumption consumption Features. DS18B20 allows us to build a temperature measurement system that is suitable for our own economy.
Performance characteristics
① Use single -line special technology, which can be used through the serial port, or the microcomputer interface through other I/O port lines. It does not need to pass the other transform circuits to directly output the temperature value of the test temperature (9 binary numbers, including symbols) , ② The temperature measurement range is -55 ° C-+125 ° C, the measurement resolution is 0.0625 ° C, ③ contains 64-bit read-only memory ROM, ④ adapting to various single-chip machines or system machines, ⑤ users can set separately separately, respectively Determine the upper and lower limits of the temperature, and the parasitic power supply in the ⑥ inside.
Control Method
In terms of hardware, there are two ways to connect the DS18B20 to the single -chip microcomputer. GND ground, I/O pick -up machine I/O. Whether it is internal parasitic power supply or external power supply, the I/O ports should connect a pull -up resistance of about 5kΩ.
Temperature measurement device based on AT89C51+DS18B20
The temperature sensor of the temperature measurement device based on DS18B20 DS18B20 transforms the measured environmental temperature into a digital signal with symbols. The sensor can be placed anywhere within 150 meters away from the device. For the pull -up resistance, the sensor is powered by external power. 89C2051 is the core of the entire device. 89C2051 with 1K byte Flashrom, the user program is stored here. The display module consists of a four -bit co -alarm digital tube and 4 9012. The system program is divided into two parts: sensor control program and display program. The sensor control program is prepared in accordance with the communication protocol of DS18B20. The system of the system is to complete the reading and writing of the sensor and the display of temperature under the program control. Smart thermostat development.
Precautions
Although the DS18B20 has the advantages of simple temperature measurement systems, high temperature measurement accuracy, convenient connection, and small occupation lines, it should also pay attention to the following problems:
(1) When reading and writing programming DS1820, it is necessary to strictly ensure the timing of reading and writing, otherwise the temperature measurement results will not be unable to read. Essence
(2) When the DS1820 hanging on the single bus is more than 8, the bus drive problem of the microprocessor needs to be solved.
(3) When using the DS1820 for long -distance temperature measurement system design, it is necessary to fully consider the problem of the distribution capacitance and impedance matching of the bus.
(4) DS18B20 requires a certain conversion time from the end of temperature to the end of the temperature to the digital amount.