Weak current College】 【RF card design water control Terminal.

Summary: with the computer, micro-electronics and industrial communication technology, these issues have been a better solution, this article describes an approach based on CAN bus and RF card technology water control terminal design.

With the increasing shortage of water resources, water has become the water units, the entire country and the countries of the world. In our country, the water there is a huge waste of, the existing policy also has the technical level. To implement modern management of water, water control terminal of development and improvement is an important subject. A high degree of automation of water and control Terminal is designed to address many of the technical issues, including: valve control, authentication, water payment, data acquisition, data management, etc. With the computer, micro-electronics and industrial communication technology, these issues have been a better solution, this article describes an approach based on CAN bus and RF card technology water control terminal design.

I. Introduction to radio frequency card technology

Current common IC card has two kinds: contact and contactless IC card. Contact IC card through mechanical contact gets energy from the reader and the exchange of data, broader application, but sometimes mechanical contact on unreliable, and contacts can easily be corrosion and pollution, and in some areas of the application is restricted; non-contact IC card through the Induction coil RF from the reader Gets the energy and the exchange of data (also known as RF card), which store large capacity, low cost, applicable to certain places with special requirements. Contactless identification has gradually developed into an independent interdisciplinary expertise, involves high-frequency technology, semiconductor technology, data protection, cryptography, telecommunications, etc, it will come from different professional areas of technology application integrated with the already mature.

RF card card electrical parts from an antenna and ASIC. Card of the antenna is some set of winding of coils, suitable package to the card. The card consists of a high-speed ASIC (106KB baud rate) RF interface, a control unit and a 8K bit EEPROM. Card is divided into 16 sectors, each slice consists of 4 blocks (block 0, block 1, block 2, block 3), 16 sectors of 64 block in absolute address number for 0 to 63. The card's stored content by user-defined according to the needs, the following is an identity system storage scheme, as shown in Figure 1:

Second, water control Terminal hardware design

The main water control terminal for data display, user identification, consumer data storage, parameter, save, black/white list retrieval, CAN data communication, flow pulse acquisition, electromagnetic valve actuation functions.

1. RF card driver circuit:

Selection of Fudan company FM1702 or Philips RC500, the two chips are based on standard ISO14443 contactless card reader chip, support ISO14443typeA contactless communication protocols, support MIFARE standard encryption algorithms. Chip internal height integrates analog modulation and demodulation circuit, you only need a small amount of peripheral circuits can constitute a read-write card circuits.

Antenna resonant frequency adjustments difficult, there are conditions it is best to use the impedance Analyzer, can accurately receive antenna resistor of matching parameters, the impedance analyser is expensive, no such equipment condition of designers you can use the dual-generally track oscilloscope with lissajous graphics method or based on the empirical formula of data repeatedly try to scrape together you can get a good card.

2.CAN communication circuit:

The CAN communication controller SJA1000 (data link layer chip) and level translator 82C250 (physical layer devices). Peripheral circuits SJA1000 and communications program has a very mature programmes and information can no longer describe here for reference. To fully exploit the advantages of CAN bus technology, should be adopted to improve CAN2.0B communication efficiency. Baud rate selection according to the communication distance, do not blindly pursuing high baud rate, the baud rate is too high can cause communication errors, but will reduce the communication efficiency.

CAN bus does not provide an application layer protocol specification, a strong application layer protocol on the application of the system is essential, if the application layer protocols, more complex, CANOPEN or DEVICENET can refer to the standard agreements.

3. data storage circuits:

By fram FM24C256 and FLASH memory AT24C256. Use the FRAM FM24C256 storage consumption data, while the costs are relatively high, but writes up to 10 billion times, ensuring the reliability of data storage. Select FLASH memory to store blacklist information AT24C256, is this part of the data written is not very frequent and AT24C256 lower cost.

4. display circuit:

Use seven segment led or LCD module. Depending on the users site use environment. If you use the ambient temperature is maintained at 10-30 degrees Celsius, and there are no special mechanical strength, waterproof sealing requirements, it is recommended that you use the LCD module, because the LCD module with display content-rich, intuitive, elegant appearance, low power consumption of benefits. But if you use the site is the ambient temperature range is large, and there are water-proof seal requirements of occasions (such as baths, etc), then display to choose digital tube.

5. sampling circuit: flow measurement of water control Terminal usually with meter pulse sender, sampling circuit current limiting resistors and mainly optocoupler.

6. valve driver circuit:

Valve drive circuit for switching water control valve control valve, solenoid valve used to driving circuit is simple; if the water control valve with ball valve, then consider reversing, the driver may be slightly more complexWith single pole double reset type relay driver for ball valve, due to the relay contacts service life limited, often using four transistor for reversing the ball valve drive circuit for power supply.

7. the clock circuit:

Water control Terminal has a real-time clock is necessary, particularly in the e-card and billing system, the consumption of water data must have a time-scale, to identify consumption data of the order, to meet a variety of billing methods. This design uses a serial clock chip DS1302, DS1302 is of small size, low price, the interface is simple, provide advantages of trickle charging, thus becoming the most popular clock chip DS1302 external button batteries constitute the clock circuit:

3. water control Terminal parameters configuration

The following briefly describes the parameters of the water control Terminal configuration, so that readers on water control Terminal features a more comprehensive understanding. Because the user needs may be more complex, and the user requirements for the Terminal parameters to configure from flexible, Central Online require a Terminal parameters can be set via the CAN network and stored in its non-volatile memory. The specific meaning of each parameter is as follows:

1. the sector code: PC management software, has established a water sector at all levels of the tree structure, and to each sector code assigned to the sector. Individual water control terminal attached to a Department, "Dept Code," property as shown in the Terminal where they are located. And "Dept Code," also appears in the terminal uploading of consumption data to support management software implementation by Department for statistics and the clearing of water consumption.
2. work in the sector: the attribute identifies the Terminal to identify MF1 RF card which sectors.
3. black/white list: this property identifies the Terminal work in the blacklist or whitelist mode.
4. open status: whether the properties determine terminal respond to the user's credit card operations, this property can be used to remotely shut down the Terminal.
5. filtering time: as the Terminal receiving traffic signals is the width of a pulse sequence (i.e. Wiegand signal), may be affected by the interference of the clutter, the parameter determines the end of the filter constants, the terminal will be able to receive the narrowest pulse width.
6. Pulse equivalent: this property identifies each premium corresponding pulse number.
7. ball valve stroke: the attribute determines the Terminal output open valve signal length of time, also determine the ball valve to open degree.
8. device status: this property identifies the end own current alarm or working conditions.
9. no card has the pulse beep: when the valve or the terminal controller valve driver circuit failures can occur even if the user is not a credit card or water, when this occurs, the Terminal should be timely and progressive machines and alarm. This parameter gives the result "no card pulse alarm" threshold.
10. card no pulse alerts: when flow sender or terminal controller sampling circuit failures can occur even if the user does not charge card, when this happens, the Terminal also should promptly up bit machine alarm. This parameter gives the result "has the card no pulse alarm" threshold.
11. Terminal address: this attribute determines whether terminal equipment in the CAN network address and is unique.
12. the terminal device type: this parameter has three available options: credit card terminal, remote metering Terminal, access control Terminal
13. the Terminal measurement types: this parameter has four alternatives: running water, hot water, boiling water, constant temperature bath water
14. Terminal account type: this parameter has two alternatives: public account Terminal, personal consumer Terminal
The user may be required for all kinds of water control terminal equipment is available for the above three types combined description.
15. user code and seed keys: these two properties are encrypted and card-related parameters.

IV. concluding remarks

As civil product, the price factor is very important. In programme design and device selection process should be adequate in function, try to reduce costs, but also must consider the product's reliability and stability index, which requires designers technical plan carefully to find the best price/performance of the product.

Innovation point of this article the author:

1. current water control terminal communication way almost all the way, there is the RS485 slow, reliability is poor, communication distance is short, and many other issues. CAN bus technology could very well solve the above problem, CAN bus technology while in the field of industrial automation control has been widely used, but in water control system application in the CAN-bus technology, is a relatively new application scenarios.
2. This article provides a complete set of water control Terminal parameters settings, you can adapt to different functional requirements of water control system. This scenario proven design reasonable, full-featured, for similar systems, the higher its value.

Reference documents:

1.CANopen Protocol _ popular European CAN-bus layer protocols
http://www.zlgmcu.com/philips/can/CANopen.asp
2. Yang Hsien-Hui, industrial data communications and control network/new information control and system series textbook, Tsinghua University Press
3. the text of the copies of his son's remolding thought RF card read-write module Design Department of electronic engineering of Beihang University
4. Liu Tianhua, smart RF card at the campus one-card system of micro-computer information 200635 period