Wireless temperature & humidity monitor and control system

Transcription

1 Wireless temperature & humidity monitor and control system ang Zhou 1, Qiaodi Zhou 2, Qingpeng Kong 3, Wenyu Cai 4 Hangzhou dianzi University Electronic information institute, Hangzhou ,China Abstract The traditional cable data transmission is high cost and big interference.instead,the wireless data transmission has advantages like: low cost,better applicability and lower interference.so,a kind of handheld wireless temperature and humidity control system based on the msp430 microcontroller, wireless transceiver module and DHT11 temperature and humidity sensor is designed. This system not only can receive data by hand-held device, but also can connect to computer with RS232 line. In this paper, software and hardware design ideas have been givn. The practice usage indicates that the system is stable, power consumption is small, and can be used in various occasions where the temperature and humidity data is needed. terminal. The temperature and humidity measure system is mainly responsible for the temperature and humidity data acquisition and send. Receiving terminal receivs data from the distant, and display on the LCD. The receiving end is also responsible for temperature and humidity alarm and connecting with PC. In Special circumstances the receiving terminal can also send control information to temperature and humidity measurement system, in order to control the temperature and humidity. The temperature and humidity measure system data transmission Receiving terminal RS232 Keywords-wireless; temperature and humidity;,dht11;msp430. I. ITRODUCTIO In daily production and life, we often need to know the temperature and humidity value of the certain place If we use cable to transmit data, it will cost a lot, but the wireless communication costs less, it establishes a connection between the buildings in a very short time, and error rate is quite low. Therefore, in the environment which cable can't be used, the wireless communication is more practical.and if the receiver is made into hand-held, the flexibility will increase greatly. At present, this kind of low power wireless data transmission technology is widely used in industrial and civil field. II. THE STRUCTURE OF WHOLE SSTEM A. Design ideas The System can be devided into data acquisition part, hand-held data receiving part. As is shown in figure 1, the first part is the temperature and humidity measure system, the second is temperature and humidity receiving and display B. System model Figure 1. System overall structure. Data collection end:the data collection end consists DH11 temperature and humidity sensor, msp430 processor, and module, other parts are fans and humidifier. The structure shows in the figure 2: Fan Humidi fier Figure 2. MSP430 DH11 Power The structure of temperature and humidity collection end. As the figure shows, DHT11 collects the temperature and humidity data, these data are handed to the after processed by the, The system works as soon as power on. Data are collected every period of time. Fan and humidifier are controlled by, when the temperature and humidity valves are larger than a certain value, the /12/$ IEEE 2246

2 corresponding switch will be turned on, in order to control the temperature and humidity in the certain circumstance. Data receiving end The receive module mainly consists msp430 microcontroller, module, indicator LED, alarm buzzer, LCD display etc. the structure is showed in figure 3.As the figure shows, when the data are received by, the real-time temperature and humidity data will be displayed on the LCD after the treatment of the, the fan indicator and the Humidifier indicator are designed to show wether the corresponding device is working at this time of the Data monitoring end. In addition, the module has RS232 interface, it convenient to conncet with PC, it is more intuitive to show the change of temperature and humidity. Fan indicator Humidifiers indicator Buzzer Figure 3. MSP430 RS232 interface Structure of temperature and humidity receiving III. SSTEM HARDWARE A. wireless transceiver module LCD Power is low cost wireless transceiver below 1 GHz, designed for wireless application with low power consumption. The main circuit is for ISM (industrial, scientific and medical) and SRD (short distance equipment), frequency band in 315, 433, 868 and 915MHz, but can easily programme to work in other frequency,such as MHz, MHz and MHz. is improved from the CC1100 RF transceiver and compatible with CC1100. s main improvements lile: improved pseudo response; better closing phase noise, thus improve the adjacent channel power (ACP) performance; higher input saturated level; improve the output power cant; expanded working band. provides 6 I/O ports and can be connceted to the directly.the SCLK, MISO, MOSI, CSn are SPI interface and responsible for working mode switching, RF channel choice, RF power Settings etc. GDO1, GDO2 pins are used as a general digital output (DO), also can be used as one of the four function :test signals, FIFO state signals, always output, continuous data input. The pecific connection showed in figure 4: 3.3V MOSI MISO CSn SCLK GDO0 GDO1 Figure 4. connection. workflow: 1. Initialize SPI pins 2. reset. 3. initialization. (the status can be read from the SO pin). Switching CC1100 to the IDLE state after initialization. 4. State swithcing, write/read FIFO data. In this system, works in the 433 MHz, 20 Mw, effective distance is about 200 m. B. Msp430 microcontroller Msp430 was released by the U.S. TI (Texas instruments) company in 1996.It s a 16 bits mixed signal ultra-low power processor. It contains many peripherals such as ADC and DAC, simulation comparator, common digital module (such as SCI, SPI, the I2C, the watchdog, PWM, CAP, time/timer) inside the IC. so can reduce the complexity of the peripheral control circuit, save PCB space, also reduce design costs, improve the reliability of system. It completely meet the requirements for general application. Its main characteristics are: 1) low power consumption; 2) strong processing ability, single cycle instruction, hardware time-multiplier inside; 3) high-performance simulation technology and rich chip peripheral modules; 4) high stability, industrial products; 5) convenient, efficient development environment; 6) Adapt to wide rang of temperature, Strong anti-interference ability 7) small and flexible, cost-effective. In order to adapt to the industrial operation environment,msp430 s microcontroller working temperature is-40 C ~ + 85 C, the product can operate in industrial environment stably. 2247

3 C. DHT11 temperature and humidity sensor The DHT11 is a digital signal output temperature and humidity sensor which is already be calibrated.it uses the digital acquisition technology and temperature and humidity sensor technology. The sensor includs a resistive humidity measure component and a TC temperature sensor component.the connection with a 8 bits high performance Single-chip microcontroller gives the sensor excellent quality, super fast response, anti-jamming ability, high cost-effective. DHT11 offers an I/O port to connect with the msp430. the 40 bits humidity and temperature data send to the microcontroller at every time, data are checked by CRC. So the accuracy of the data is guaranteed. DHT11 s power consumption is quite low, 5 V power supply voltage and the maximum average current is about 0.5 ma. DHT11 digital temperature and humidity sensor connection circuit is simple, just needs one I/O port to connect to the. The typical application circuit is showed below : The sends a signal to start (low level), DHT11 switches itself from low speed mode to high-speed mode, and then gives the response signal as soon as the ending of start signal, triggers a data acquisition, then 40 bit data will be sended,at this time the temperature and humidity data can be read from the I/O port. D. LCD character type (i.e. show 16x2 characters) LCD module is widely used in different occasions, and all kinds of LCD manufacturers offer almost the same 1602 module or compatible module.many manufacturers offer different backlit color of display module. Its working voltage is 5 V, working current 2.0 ma, shows 16x2 characters once a time. The LCD1602 has 16 pins, in addition to the power and, the others are D0-D7 data I/O ports and backlight control ports. The connection circuit shows in figure 7: VDD VDD DATA DHT11 Figure 5. Typical application circuit. DHT11 uses a single bus data format. That is, a single data port completes input/output two-way transmission. One single packet is 5 Byte (40 Bit). Communication time is less than 3 ms. The specific format shows in the following figure. a full data transmission contains 40 bits, high bit comes out first. Data format: 8 bit humidity integer data + 8 bit humidity decimal data + 8 bit temperature integer data + 8 bit temperature decimal data + 8 bit calibration.the calibration is the sum of the first four bytes. Humidity Temperature CRC Integer Decimal Integer Decimal Figure 6. DHT11 data output format. D0 D7 E LCD1602 R/W RS VL 5V 10K BLK BLA Figure 7. LCD1602 and connections. E. RS232 interface RS-232 is a serial physical interface.the standards are made by Electronic industries Association EIA (Electronic Industry Association). RS is short for "recommend standard", 232 for identification number. RS-232 bus has 25 standard signal lines, including a arteries and an auxiliary channel. In most cases we use the main arteries.in general communication usage, only a few signal lines are needed a sending line, a receive line and ground line. There is a 232 interface on the receiving module, it can conncet to PC with a cross RS232 line, so the temperature and humidity data can be sent to the 2248

4 PC. The baud rate is 9600, 8 bits of data, a stop bits, no parity, the largest transmission distance is about 15 meters. IV. SOFTWARE DESIG A. Data collection Data collection end uses DHT11 to get temperature and humidity data, 4 bytes of temperature and humidity data are send to the after the treatment of msp430.one packet includes 1 byte of preamble byte, 2 bytes of sync word, 1 byte packets length, 1 byte address, 4 byte packet size, 2 bytes fan and humidifier state information, 2 bytes of CRC check. Figure 9. Data send flow. Figure 9 is data sending flow chart.the microcomputer and module initialize after power on. The reads DHT11 after a starting signal, and then judges whether the temperature and humidity data are larger than the setted threshold,if it does, fan and humidifier will turn on to control the temperature and humidity.at last the data will be sent directly if in normal range. Data receiving part is used to filter packets and display. The specific flow shows in figure 10: Preamble bits sync word length Address Data status CRC Start Figure 8. Frame format. Msp430 initialize The preamble byte and sync word are set by initialize configuration register,the module will add themto the beginning of a frame. Because CC110 is very sensitive, in IDLE mode, it also has some garbled output, in order to make sure the data is correct, the address byte is needed, receiving end receives or rejecte data by wether the address is correct or not. set to the RX mode Data receiving Address correct? Data reject Start temperature and humidity more than threshold? Turn on indicator and buzzer Display Msp430 initialize Figure 10. Data receive flow. initialize set to the TX mode DHT11 Data collection Data more than the certain value? Open fan or humidifier The data are not directly to show on the LCD when received. At first,the judges wether the source address is correct, then,then checks fan and humidifier state, these two bytes control the indicator lights and the buzzer on hand-held devices.,at last the real-time temperature and humidity are displayed on LCD. V. TEST AD SUMMAR Sending data 2249

5 Figure 11. Data are shown on PC through RS232 line display the real-time temperature and humidity data and the status of temperature and humidity control devices,but also can communicate with PC.By test, this system s mainly features are : reliable performance, the transmission distance 200 M,low error rate, high precision, convenient installation, low cost. It can be widely used in various occasions where the temperature and humidity control is needed. ACKOWLEDGMET This work is supported by the ational atural Science Foundation of China (O ) and Zhejiang province key scientific and technological innovation team project (O.2010R50003). As is shown on figure 11,data are received by a PC.because the preamble byte,sync word and CRC bytes are sent by automatically,so 8 bytes are displayed in the textbox above.the first one is length 0x08,four bytes of temperature and huminity data are shown followed by adress 0xaa. The last two are status informations. This paper designs and realizes a kind of temperature and humidity control system by wireless transceiver module. The handheld receiving equipment can not only REFERECE [1] Liu Wei,Zong Xiaoping, Wireless temperature and humidity collection system design, heibei.china,vol. 27,2010,pp [2] Huang Jianwei. The wireless temperature measuring system based on DS18B20 henan.china,vol. 29, 2010,pp [3] ue Pengxia. Wireless temperature and humidity data acquisition system, shanxi.china,vol. 2,2009,pp [4] Lu Chao. Wireless temperature and humidity monitor device for Greenhouse, shanxi.china,vol.7, 2011,pp [5] Qiang unxiao,wu Fengbo. Wireless temperature and humidity measure and control system based on ZigBee technology, shanxi.china,vol.38,2009,pp