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How To Test ds18b20

2017-06-19 16:15:11 | 日記

With the development and progress of society, the requirements of the temperature is becoming more and more strict on many occasions, the application of temperature monitoring system has been paid more and more attention. In the field of agricultural development, agricultural greenhouses, cold storage, incubation of greenhouse and many other occasions need temperature measurement technology. The traditional temperature measurement system is a wired system, for some need more temperature measurement occasions, the use of traditional wired temperature measurement in the layout, maintenance and update there are many inconvenience. In order to solve this problem, a wireless temperature monitoring system based on single chip and wireless transceiver module is designed. It is very convenient to construct a multi - point distributed intelligent wireless temperature monitoring system with temperature sensor.

Wireless temperature monitoring system
The system consists of two parts. As shown in Figure 1, the first part is the node temperature measurement system, the second part is the temperature display management terminal. The node temperature measurement system is responsible for measuring the temperature and sending the temperature value to the temperature display management terminal via wireless communication. The management terminal receives the temperature information and displays and sends out the alarm signal, and in special case the management terminal can also send the control information to the node temperature measurement system in reverse to realize the temperature regulation.This paper will tell you how to test ds18b20 .

Design of Node Temperature Measurement System

Node temperature measurement system structure shown in Figure 2, the system core control chip AVR series of single-chip ATmega16. This is a compact instruction set of single-chip, high speed, low power consumption, with Sleep function and CMOS technology, and has a high degree of confidentiality, can be programmed several times Flash, with multiple password protection lock function. Also built-in watchdog timer (WDT) and chip with RC oscillator, it is very convenient to use. With a sleep power-saving features and idle low-power function, in terms of practicality is relatively high cost. However, there are many electronic component distributors to supply.

Temperature sensor module using digital temperature sensor DS18B20, it is the United States Dallas Semiconductor introduced a smart digital temperature sensor. DS18B20 in connection with the MCU only need a line (that is, a single bus interface, plus power for the three-wire interface) to achieve the microprocessor and DS18B20 two-way communication. Using the DS18B20 can save system resources and make the system architecture easier. DS18B20 temperature range is -55 ℃ ~ +125 ℃, the inherent temperature resolution of 0.5 ℃. Power supply is 3 V ~ 5V / DC. In the use of no external components, the measurement results in 9 to 12 digital serial transmission. DS18B20 internal structure is mainly composed of four parts: 64-bit lithography ROM, temperature sensor, non-volatile temperature alarm trigger TH and TL, configuration register. Where the 64-bit lithography ROM stores the address sequence number of the DS18B20. (48H) is the product type label, followed by the 48-bit DS18B20 itself is the serial number, the last 8 is the first 56-bit cyclic redundancy check code (CRC = X8 + X5 + X4 +1). The address sequence code in the lithography ROM can distinguish between each DS18B20, thus enabling multiple DS18Bs to be mounted on the same bus. According to the DS18B20 communication protocol, MCU (single-chip) control DS18B20 to complete the temperature conversion must go through three steps:

(1) DS18B20 should be reset before each read and write

(2) After a successful reset, send a ROM instruction

(3) Finally send the RAM instruction

NRF24L01 is Nordic's highly integrated single-chip wireless transceiver device. Chip with automatic response and automatic retransmission function, the speed of up to 2 Mbps, 126 optional work channel, a very short channel switching time, can be used for frequency hopping, the output power, channel selection and protocol settings can be carried out through the SPI port Set up. Its Enhanced Shock Burst mode can simultaneously control the response and retransmission functions without increasing the workload of the microcontroller. NRF24L01 also has the same channel to receive six different channel data function, the use of FDMA technology can achieve up to 750 points of data collection, which makes it a wireless temperature measurement system hardware to achieve the best choice. NRF24L01 module in the data transmission with the MCU, you can use the MCU general I / O port, the system directly using ATmega16 inherent resources SPI communication port, so to a certain extent, simplifies the software design process. You may be interested on: how to use 74hc595.

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