DS18B20 digital temperature sensor in the use of attention to matters
small hardware overhead need to compensate relative complex software, because the DS1820 and serial data transfer between microprocessors, therefore, in the programming of DS1820, speaking, reading and writing, must be strictly guaranteed to read and write timing, otherwise will not be able to read the temperature measurement result. In the use of PLM, C and other high-level language for system programming, the part of DS1820 operation had better use assembly language implementation.
are not mentioned in the relevant data of DS1820 DS1820 hung on single bus number problem, can make people easily mistaken for hanging any number of DS1820, not in the practical application. If the hang DS1820 single bus is more than eight, you need to solve the problem of the bus driver of the microprocessor, this in multi-point temperature measurement system is designed to be attention.
connection DS1820 bus cable length limitation. Experiment, when adopt ordinary signal cable transmission length of more than 50 m, read the temperature measurement data error will occur. When take bus cable instead of twisted pair shielded cable, normal communication distance is 150 m, when using twisted per meter more twisted pair with shielded cable, normal communication distance is further extended. This kind of situation is mainly by the bus signal waveform distortion caused by distributed capacitance. Therefore, in the use DS1820 for temperature measurement system design should fully consider long distance bus distributed capacitance and impedance matching problem.
in DS1820 temperature programming, sent DS1820 temperature conversion after the command, the program will always waiting for the return signal of DS1820 once a DS1820 is bad or break line contact, when the program is to read the DS1820, there will be no return signal, the program into the infinite loop. This point in the DS1820 hardware connection and software design to give some attention.
temperature shielded twisted-pair 4 core cable recommended, including a couple line grounding line and signal line, the other set, VCC and ground the shield at the source end single point grounding.
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key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor