Design of Control System of GPS-based Tower Clock

Transcription

1 Key Engineering Materials Online: ISSN: , Vol. 568, pp doi: / Trans Tech Publications, Switzerland Design of Control System of GPS-based Tower Clock Wei Hong 1,a, Zhou Guoping 1,b, Ding Jianwen 2,c 1 College of Information Science and Technology, Nanjing Forestry University, Nanjing , China 2 College of wood Science and Technology, Nanjing Forestry University, Nanjing , China a wh @tom.com, b Zhougp@njfu.edu.cn, c dingjianwen@njfu.edu.cn Keywords: GPS; servo motor; MCU; real-time adjusting Abstract. The design consists of STC89C51 MCU, the GPS15-XL receivers, LED display, servo motors, voice timekeeping and other components.and it is the GPS control system for tower clock, with timekeeping, display, automatic error correction functions. The design captures accurate time information from satellites by GPS15XL-W receiver chip, and collects and deals with time information received from SCM. And then it adjusts the clock. The SCM system consists master clock, and drives the secondary clock through giving out pulse to a servo motor. The system can also achieve the automatic error correction after power on, to change inconvenience of the traditional correction, reduce the mechanical errors. And the tower clock accurate up to ±1µs. There is no cumulative error. Introduction Tower clock is often found in large buildings, stations, terminals, churches, squares, tower and other places, where population is density, the passers always require the exact time to plan a trip. If there is the exact time, the trip will not be delayed, so as to protect people's travel and the normal safe operation of such equipment. Moreover, with the economic and social development, people gradually accelerate the pace of life, people have become increasingly demanding the precision of time. Though the city's tower clock is more, most is based on traditional tower clock-based transmission, manual timing. Traditional tower clock driver is purely mechanical control, and working is instability, you need check the time artificially. Now the tower clock, generally small-scale integrated circuits control the stepper motor to go, the entire system is bulky, accuracy is not high. Therefore, the design of the real-time adjusting tower clock became a critical research. GPS time synchronization technology is currently more mature and widely used in the international time synchronization. In addition to the current international U.S. GPS system, there are GLANASS the former Soviet Union and China's "Compass" system. GLANASS system due to economic reasons, the number of healthy stars is limited, the stability and reliability can not be guaranteed, "Compass" system has not been civil, and can not be covered in real-time. GPS is now more mature and reliable system. GPS is the short of Navigation Timing and Ranging Global Positioning System, which is the second generation of the development of global positioning system and researched by the U.S. Department of Defense in the late 1970s [1]. GPS navigation has been widely used in navigation, precision measurement, high-precision timing, vehicle location and security fields, the development is very fast, and there is constantly cross-industry development. The hammer is the power source of ancient mechanical tower clock, which took the needle through the mechanical transmission driven institutions to indicate the time, and gave the correct time by tapping a special "clock". Modern electrical and mechanical tower clock of the needle is mechanical; control system is the picture-minute form. Tower clock is the sub-clock, which receives high-precision electrical pulses sent by the master clock (usually quartz) regularly, and takes the needle through the stepper motor driven institutions to indicate the time, and synchronized with the master clock. Chime bells or music issue from the audio tape or program control. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-12/05/16,03:59:39)

2 158 Machining and Properties of Material and Manufacturing Technology Currently, most GPS research is based on the research of navigation, the research for the timing has just started, GPS precision timing can not only provide accurate time, you can also make the electricity network of transportation and communication sector to achieve time synchronization, such as the Internet computers, CDMA base stations, etc., need to synchronize with the UTC time. The use of GPS-OEM receiver board, a second research and development to achieve time synchronization, compared with the traditional timing, which has high precision, good stability, no accumulated error, and are limited without geographical, climatic and other environmental conditions, cost-effective and easy to operate and so on. "GPS tower clock" appeared in Although the GPS tower clock come on the market, the technology is immature and many issues must be further studied, such as the GPS timing solutions, the mechanical sub-clock rotation program and control systems. With the rapid development of electronic technology, people are increasingly demanding time synchronization, and GPS clock synchronization is the trend [2,3,4]. System Design The design is the use of the GPS tower clock with a precision of GPS timing, the microprocessor control system for the master clock in the form, tower clock is the secondary clock which receives the pulses from microprocessor and drives the pointer through the servo motor to achieve time synchronization, timing device realizes through a special voice chip [5]. The system consists of the following components: system control module, receiver module, display module, the keyboard module, motor module, voice module, shown in Fig.1. receiver module motor module System Control Module Fig.1. System Block Diagram display module voice module keyboard module GPS timing mode uses GPS as a standard clock source, with single-chip circuit as the core controller chip, the use of hardware and software approach, so most of the hardware circuit is replaced by a software program and the circuit structure is simple, convenient debugging, low cost, highly automatic and reliable. Hardware Design The choice of microprocessor. The microcontroller is STC89C51RC in my design. It is a new generation single-chip of powerful anti-interference, high speed, low-power, which designed by Hongjing technology, and whose code is fully compatible with traditional 8051, 12-clock /machine cycle, and 6-clock/ machine cycle can be arbitrary choice, the latest version of the D integrated MAX810 reset circuit. Security classification is strong and price is ultra-low [6,7,8]. Features: 1. Enhanced 6-clock / machine cycle, 12-clock / machine cycle 8051CPU, 2. Voltage: 5.5V-3.4V / 3.8V-2.0V, 3. the operating frequency Range: 0-40MHz, the equivalent of an ordinary MHz, the actual operating frequency up to 48 MHz, 4. the user application space: 4k, 8k, 13k, 16k, 20k, 32k, 64k bytes, 5. Integrated 1280 bytes, 512 bytes ram, 6. EEPROM, 7. Watchdog, 8. The operating temperature 0-70 degrees (Celsius).

3 Key Engineering Materials Vol The choice of GPS receiver module. Common GPS receivers are a lot, such as the SiRF-starIIe, SiRF-starIII, Sony-single chip solution-cxd2951, Evermore, Garmin, and so on. Compared with others, the design options is the United States GARMIN series GPS15xl-w, it is the economic card, parallel 12-channel GPS receiver, which can track 12 satellites, high precision, low power consumption. GPS real-time differential accuracy is 3-5 meters, and it support WAAS function. It is compact, easy to use, and information of the receiver can be easily displayed on the display unit or the PC. Fully shielded package, excellent anti-electromagnetic interference characteristics are its characteristics. Users do not need initialization, installation, receiver navigation data can be automatically transferred, it has strong anti-blocking capability, reliable performance. [9,10]. Motor selection. The differences between common stepper motor and servo motor are as follows. Comparison shows that the servo motor main advantages: good speed control characteristics throughout the region can achieve smooth speed control, almost no oscillation, high efficiency is up to 90% and no fever, speed control, high-precision position control (depending on what encoder), constant torque within rated operating region, low noise, no brush wear, maintenance-free, no wear particles, no spark, and it is suit for clean rooms, easily violent environment [11,12]. Therefore, the design chose the Yaskawa servo motor SGMAH-04AAA4C, the power is 400w, the voltage is 200v, the current is 2.8A, and the speed is 3000r / m. Voice module selection. The voltage of ISD4002 series is 3v, the single recording time is 4-8 minutes, and the sound quality is good for mobile phones and other portable electronic products. Chip uses CMOS technology, contains the oscillator, anti-aliasing filter, smoothing filter, audio amplifier, automatic squelch, and high-density multi-level flash storage display. Chip design is based on the microcontroller, and all operations must be controlled by it, operation commands deliver via the serial communication interface (SPI or Micro wire). The chip uses multi-level direct analog storage technology, the value of each sample directly store in the flash memory chip, so it can be very real, natural reproduction of voice, music, tone and effect sound, and avoid quantization noise and the "metal sound" caused by the quantify and compression of solid recording circuit. Sampling frequency can be 4.0, 5.3, 6.4, 8.0 khz, the frequency is lower, the recording time is longer, while quality has declined, on-chip information stored in flash memory, you can save the information 100 years (the typical values) in the case of power failure, and repeated recording 100,000. Function keys Antenna GPS15LX-W Reset STC 89C51RC LED display ISD4002 Servo motor Servo LM386 Implifier Speaker Output Fig.2. System Block Diagram System Block Diagram. According to design requirements, the system include antennas, GPS OEM receiver module, single-chip signal processing circuitry, EEPROM memory, timer circuit, the speaker, and four parts of the antenna, GPS-OEM receiver modules, single-chip signal processing circuit, the main control circuit connect in series, EEPROM memory, timer circuit, display circuit respectively connected to the main control circuit in the branch structure, timer circuit connected with the speaker in series. The system block diagram is shown in Fig.2. System hardware design schematics is shown in Fig.3.

4 160 Machining and Properties of Material and Manufacturing Technology Software Design Fig.3. System schematics circuit The system software design has two main parts: the clock system controlled by the microcontroller and real-time adjusting system received information from the GPS receiver, the former is simpler, so I do not repeat them here, only introduce the adjusting system. GPS-synchronized timing solutions selection. GPS time adjusting can be divided into two types: pulse interrupt and serial communication interfaces. GPS time information itself is very accurate. But which approach is suitable to the automatic protection device in real-time clock chip timing, it becomes crucial to ensure time accuracy. We choose the serial communication to meet the basic requirements for tower clock [13,14,15]. Serial communication is output time information by the way of the serial data stream, each automatic protection device receives serial time information once per second to synchronize time. During time adjusting, sending and receiving serial data use interrupt mode, the two sides of the interrupt handler will take up the CPU time, and the size of the delay connects with both serial port interrupt priority. In addition, in serial communication, the data transmission is bit by bit according to a certain baud rate, the bus transfer will be delayed, the size of the delay connects with the baud rate and the volume of data. In the above various factors which affect the accuracy of the timing, the transmission delay can only be accurately calculated, the others can only be roughly estimated. From all accounts, we can give a correct value to the time information to ensure that timing accuracy. To obtain GPS standard time information. GPS2OEM board use NMEA20183 communication standard format, it can output a variety of sentences which are at the beginning of "$". We extract the statement from "$ GPRMC", $ GPRMC, <1>, <2>, <3>, <4>, <5>, <6>, <7>, <8>, <9>, <10>, <11> 3 hh <CR>, <LF>.The figure below shows the software compilation window: Summary Fig.4 WeiFu software compilation window In system design, we completed the following sections: 1. In the system hardware design, the devices are reliable and useful, to ensure usability, as far as possible to simplify the circuit, in the design process, we use experimental methods to complete all the software and hardware debugging; 2. The software design of the receiver module is the assembly language. We extracted accurate time information from GPS15XL-W; 3. It complete the travel time of the master clock and the display function; 4. Send a pulse to the servo motor to drive sub-minute travel time function.

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