Smart Wireless Temperature Data Logger

Transcription

1 Smart Wireless Temperature Data Logger Vivek Kumar Sehgal *, Nitin, Rohit Sharma and Vikas Hastir Department of Electronics and Communication Engineering, Jaypee University of Information Technology Waknaghat, Solan (HP) INDIA Yogeshwar Singh Dadwhal, Mitesh Bansal, Rohit Puri, Shrey Abhi Pathania and Abhay Thakur Department of Electronics and Communication Engineering Jaypee University of Information Technology Waknaghat, Solan (HP) INDIA Abstract The real time data logging of a process variable is mission critical in process dynamics. Process variables (like temperature, pressure, flow, level) vary with time in certain applications and this variation should be recorded so that a control action can take place at a defined set point. This paper proposes an 8-bit embedded controller interfaced with a temperature sensor through Analog to Digital convertor. This portable data logger is programmed to control and log the temperature variations. The temperature is displayed on a liquid crystal display (LCD) interfaced with the 8-bit embedded controller and is wirelessly transmitted to a PC communication port or a PDA communication port through Infrared/Bluetooth link. Keywords: Temperature sensor, Embedded controller, Infrared/Bluetooth link, Control Algorithm 1 Introduction A mobile temperature data logger with Infrared/Bluetooth link features was designed for applications, where portability and wireless data transfer is inevitable. Communicating reader/writer can be mounted on the wall or can be portable, too. The sensed temperature is converted to the digital form by the means of analog to digital convertor and displayed in a local LCD display. Each acquisition of temperature is compared with a user defined set point. If this value exceeds the set point a control signal goes to a final control element or a buzzer. This temperature data is also communicated to the COM port of a PC via a Infrared/Bluetooth link. Temperature is recorded using a temperature tag at user defined time intervals. The temperature tag can be programmed so that when the memory is full it either stops further recording or continues recording by overwriting the earliest of the previously recorded data [1][2]. We have implemented this Data Acquisition System using LM35 (range Celsius) sensor shown in Fig. 1. The process variable is sensed by this sensor and converted into digital 8-bit format compatible with an 8-bit microcontroller input port. The role of this embedded processor is to send this input 8-bit temperature data to the LCD display unit and simultaneously the current value of sensed temperature is compared with a set point. The set Fig. 1 LM35-DZ Temperature sensor point is adjusted by a small panel of three switches whose functions are to increment, decrement and fix the set point. The proposed data logger can also be used for other process variables like pressure, flow, humidity and level like existing models [3][4]. The main functions of proposed temperature data logger are: 1) Continuous temperature monitoring. 2) Comparison with the set point. 3) To generate manipulating signal to the final control element. 4) To display the data on the local LCD 5) To transmit the data to remote display (PC or PDA) through Infrared/Bluetooth link Since this temperature data logger is equipped with 8 bit microcontroller, it can be networked with same data loggers for other process variables in specific control applications [5] The organization of the paper is as follows: In section 2, we discuss the proposed design along with the merits over previously designed models. This section also presents the block diagram for our proposed system. Detailed circuit description is provided for each block used in this section. In section 3, we present the software implementation along with algorithm and flow diagram. In section 4, PCB designing, actual circuit implementation on PCB and simulated schematic are shown. Finally, some conclusions are offered in section 5. 2 Proposed Work In the present work, LM35 Temperature sensor is connected with the programmable embedded controller as shown in the block diagram (Fig.2) of transmitter end

2 The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling as shown in Fig. 4. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 µa from its supply, it has very low self-heating, less than 0.1 C in still air. The LM35 is rated to operate over a 0 to +150 C temperature range. 2.2 LCD Interface Fig.2. Transmitting End Block Diagram The LCD, which is used as a display in the system, is LMB162A. The main features of this LCD are: 16*2 LCD display, intelligent LCD, used for alphanumeric characters & based on ASCII codes. This LCD contains 16 pins, in which 8 pins are used as 8-bit data I/O, which are extended ASCII. Three pins are used as control lines these are Read/Write pin, Enable pin and Register select pin. Two pins are used for Backlight and LCD voltage, another two pins are for Backlight & LCD ground and one pin is used for constant change. Fig.3. Receiving End Block Diagram This work is divided into three modules, first one is temperature sensor LM35-DZ, second is 8052 microcontroller connected to LCD panel along with analog to digital convertor and third module is MAX 232 with wireless receiver and DB-9 connector. The first two modules consist of transmitting end as shown in Fig.2. And last module consists of receiving end as shown in Fig Temperature Sensor Fig. 5. LCD Interface Fig. 5. Shows the interface between the LCD and 8052 microcontroller. 2.3 MAX 232 (Communication Interface) Fig. 4. Internal Block Diagram for LM35 Fig. 6. Operating Circuit of MAX 232

3 RS-232 (Fig. 6.) was created for one purpose, to interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) employing serial binary data interchange. So as stated the DTE is the terminal or computer and the DCE is the modem or other communications device. RS 232 is the most widely used serial I/O interfacing standard. In RS 232, a 1 is represented by -3 to -25 v. while a 0 bit is +3 to + 25 v, making -3 to +3 undefined. For this reason, to connect any RS 232 to a microcontroller system we must use voltage converters such as MAX 232 to convert the TTL logic levels to the RS 232 voltage level, and vice versa. This chip is used when interfacing micro controller with PC to check the Baud rate and changes the voltage level because micro controller is TTL compatible whereas PC is CMOS compatible.. 3 Software Implementation In this work the temperature is sensed by the LM35 is converted into 8 bit data using A/D converter connected to the input port P2 of embedded processor.the program processor compares the input temperature with set point which is fixed from the switch panel. The switch panel is interfaced with port P0. If the current value of the temperature exceed the set point the buzzer beaps. The processor is programmed through Keil compiler. 3.1 Flow Chart Initially all the ports of 8052 are defined in embedded C. Baud rate is set to 1200 bps. The instruction set used and the flow of program control is shown in Fig.7. Apart from the main function, four other functions are defined for comparison with set point,display the current value of temperature and two delay functions. The call delay function ensures that the bits set at the output ports after a function call are held for a desirable amount of time. The program runs for an indefinite loop. 3.2 Algorithm of Microcontroller Operation 1. (loop 1)While power is ON. 2. Initialize LCD connected on port Enter Maximum Temperature (Default value is 0). 4. (loop 2)While switch SET i.e P0.2 (switch 3)is not If Switch INC i.e. P0.0 (switch 1) is Increment MaxTemperature Else If Switch DEC i.e. P0.1 (switch 2) is Decrement MaxTemperature End loop 2 Fig. 7. Flow Chart 5. (loop3)while switch INC i.e. P0.0 (switch 1) and switch SET i.e. P0.2 (switch 3)and Switch DEC i.e. P0.1 (switch 2)is not (we don t want current MAX Temperature to change) 1) Read the ADC connected on port 2 2) Display CurrTemp and the MAX temperature on the LCD and send the data to the Transmission port i.e. P3.1 for wireless transmission to the computer.

4 3) If CurrTemp is greater than MaxTemperature Set the Buzzer connected on P0.5 as ON ( active low). Else Set the Buzzer connected on P0.5 as OFF. End loop 3 6. Give a Delay of 5 seconds End loop 1 4 Hardware Implementation and Circuit Simulation The implemented work is shown in Fig Fig. 11. Wireless Link Fig. 12. Temperature Logging on PC Fig. 8. Complete Application Fig. 9. LCD Display Fig Microcontroller The sensed temperature from LM35, in analog format is converted into the digital 8-bit data by ADC 0809 IC chip. This 8-bit data is then sent to the input port of 8052 microcontroller.the controller then manipulates this data according to the written algorithm and perform the controlled actions.the whole hardware is implemented according to the schematic diagram shown in Fig 13.The proposed temperature logger can be used in the following applications : 1) It can be used in temperature based devices like Air Conditioners, Microwave ovens, Automobiles etc. 2) The process industries where the physical channel between sensor and display unit is not possible. 3) It can be used to control some biological processes in which temperature plays vital role, by continuously monitoring the temperature. 4) It can be used to determine the maximum and minimum temperature of the day. 5) Applications where multiple display units are required.

5 Fig. 13 The schematic diagram of the implemented hardware 5 Conclusion The necessary code has been made and downloaded in microcontroller by using appropriate software. The further extension in this work is: 1) The number of sensing elements can be increased. 2) The system is flexible to change the control algorithms like PID control algorithm. 3) A memory database can be built by using on chip memory as well as remotely connected PC through wireless link. 4) A wireless network can be built between such data loggers. 6 References [1] Radek Kuchta, Radimir Vrba, Wireless and Wired Temperature Data System, IEEE ICONS,07 pp [2] Crowley, K. Frisby, J. Edwards, S. Murphy, S. Roantree, M. Diamond, Wireless temperature logging technology for the fishing industry, IEEE - ICSENS.2004 pp Vol (2). [3] [4] logging_portable_mod8.jsp [5] Wireless Sensor Networks: Technology, Protocols, and Applications by Kazem Sohraby, Daniel Minoli, and Taieb Znati (Hardcover - April 6, 2007).