At present, the international new temperature sensor is being developed from integrated to intelligence and networked direction from integrated. Intelligent Temperature Sensor DS18B20 integrates temperature sensors, A / D sensors, registers, and interface circuits in one chip, with direct digital output, strong test and control, high transmission distance, strong anti-interference ability, miniaturization, micro power
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consumption Features. DS18B20 allows us to build a temperature measurement system that is suitable for yourself.
Performance characteristics
1 Using a single-bus-specific technology, it can be either directly output by other I / O port and microcomputer interface through other I / O port lines (9-bit binary numbers, symbol) 2 The temperature range is -55 ° C – + 125 ° C, the measurement resolution is 0.0625 ° C, 3 contains 64-bit memory ROM, 4 adapts various single-chip or system machine, 5 users can separately The upper and lower limits of each road, and the 6 containing parasitic power supply.
Control Method
On the hardware, the DS18B20 has two methods with the only one-chip connection, one is the VCC connected external power supply, GND ground, I / O connected to the I / O line of the microcontroller; the other is to power the power supply with the parasitic power supply, at this time UDD, at this time GND grounding, I / O contact single-machine I / O. Whether it is internal parasitic power or external power supply, the I / O port line is taken from 5kΩ pull-up resistor.
Temperature measurement device based on AT89C51 + DS18B20
The temperature measurement device temperature sensor DS18B20 based on the DS18B20 converts the measured ambient temperature into a symbolic digital signal, and the sensor can be placed anywhere within 150 meters away from the device, and the output foot I / O is directly connected to the P1.1 of the microcontroller, R1 For the pull-up resistor, the sensor is powered by external power supply. The 89C2051 is the control core of the entire device, and the 49C2051 FlashRom with 1K bytes is stored here. The display module consists of four integralxes of common male codes and 4 9012. The system segment sensor control program and the display program are compiled in accordance with the communication protocol of DS18B20. The system’s work is to complete the read and write and temperature display of the sensor under program control. Development of intelligent thermostat.
Precautions
Although the DS18B20 has the advantages of simple temperature measurement system, high temperature measurement, convenient connection, and less port line, but should also pay attention to the following issues in practical applications:
(1) When reading and writing in DS1820, the read / write timing must be strictly guaranteed, otherwise the temperature measurement result will not be read. .
(2) When the DS1820 hanging on the single bus is more than 8, the bus driver problem of the microprocessor is needed.
(3) It is necessary to fully consider the bus distribution capacitance and impedance matching problems when designing long distance temperature measurement systems with DS1820.
(4) The DS18B20 is completed from the temperature to convert the temperature value into a digital quantity requires a certain conversion time.