The digital temperature sensor DS 1820 of Dallas Semiconductor Company of the United States is the first temperature sensor supporting the "one-wire bus" interface in the world, in which ON-b oard patented technology is adopted. All sensing elements and conversion circuits are integrated in a triode-shaped integrated circuit. The uniqueness and economy of "first-line bus" make it easy for users to set up sensor networks, which introduces a brand-new concept for the construction of measurement systems. Now, the new generation DS 18B20 is smaller, more economical and more flexible. This can give full play to the advantages of "first-line public transport". Like DS 1820, DS 18B20 also supports the "one-wire bus" interface. The measuring temperature range is -55℃~+ 125℃, and the accuracy is 0.5℃ in the range of-10 ~+85℃. Suitable for on-site temperature measurement in harsh environment, such as environmental control, equipment or process control, temperature measurement of consumer electronics products, etc. Different from the previous generation, the new product supports the voltage range of 3v ~ 5.5v, which makes the system design more flexible and convenient. And the new generation products are cheaper and smaller [8].
1 DS 18B20 [9]
(1) has a wider voltage range, ranging from 3.0 to 5.5v, and can be powered by data lines in parasitic power mode.
(2) Unique single-wire interface mode. When DS 18B20 is connected with a microprocessor, only one port line is needed to realize bidirectional communication between the microprocessor and DS 18B20.
(3)DS 18B20 supports multipoint networking function, and multiple DS 18B20 can be connected in parallel on only three lines to realize multipoint temperature measurement in networking.
(4)DS 18B20 does not need any peripheral components in use, and all sensing components and conversion circuits are integrated in an integrated circuit shaped like a triode.
(5) The temperature range is -55℃ ~+ 125℃, and the accuracy is 0.5℃ at-10 ~+85℃.
(6) The programmable resolution is 9 ~ 12 bits, and the corresponding resolvable temperatures are 0.5℃, 0.25℃, 0. 125℃ and 0.0625℃ respectively, which can realize high-precision temperature measurement.
(7) In the case of 9-bit resolution, the temperature can be converted into a number within 93.75ms at most, and in the case of 12-bit resolution, the temperature value can be converted into a number within 750ms at most, which is faster.
(8) The measurement results directly output digital temperature signals, which are serially transmitted to the CPU through the "one-wire bus", and CRC check codes can be transmitted at the same time, which has strong anti-interference and error correction capabilities.
(9) Negative voltage characteristics: When the polarity of the power supply is reversed, the chip will not be burned due to heating, but it will not work normally.
2. The internal structure and pin arrangement of DS18B20.
The 64-bit photoetching ROM is photoetched before leaving the factory, which can be regarded as the address serial number of DS 18B20. Different device addresses have different serial numbers. The internal structure of DS 18B20 is mainly composed of four parts: 64-bit lithography ROM, temperature sensor, nonvolatile temperature alarm triggers TH and TL, and high-speed register.
Pin definition of DS 18B20:
(1)DQ is the digital signal input/output terminal.
(2)GND is the foundation of power.
(3)VDD is the input end of external power supply (parasitic power connection mode is grounded).