Abstract : In view of the current domestic heating system, which is based on a fixed-fee heating system that is extremely incompatible with the market economy, and the high price of heat meters abroad, this paper proposes to develop and design an integrated intelligent control system with low power consumption, high anti-interference ability, high confidentiality and high precision, so as to realize the metering and prepaid intelligent control of heating. Keywords : Prepaid; Heat meter; Smart card [b][align=center]Design and Development of Intelligent Heating Meter System SHAO Feng, et al (Henan Institute of Science of Technology, Xinxiang, Henan, 453003, China)[/align][/b] Abstract : Based on the current situation of the domestic prepaid heating system, which is unconformable to the market economic system and the expensive form of foreign heat, we develop a low-consumption, high-interference, high-privacy, and integrated intelligent control system with high accuracy. It realizes the measurement of heating and the prepaid fee under intelligent control. Keyword : Prepaid fee; Heat meters; Intelligent card 1. Introduction For a considerable period of time in the past, a system of bundled heating fees was implemented. "Heat" could not be considered a true commodity. There is now a consensus on how to solve this problem: it is necessary to break the old system of fixed heating fees and adopt a heat metering and charging system so that "heat" can be directly traded between producers and consumers, making "heat" a true commodity. "Whoever uses heat, pays for it." Although there are many manufacturers developing heat meters in China, there are few mature products, and no manufacturer can mass-produce heat meters. The high price of foreign heat meters is the biggest obstacle to their promotion and application in China. The localization of heat meters is the key to realizing heat metering and charging. Under these circumstances, it is of certain significance to start the research and development and trial production of heat meters. 2. System structure and pre-realized function analysis Through market research, it was found that the general structure of the current heating meter on the market is shown in Figure 1. Its main disadvantages are: (1) The temperature sensor is installed in an unreasonable way, requiring the installation of specific pipe joints. (2) The two temperature sensors are outside the heating meter, which is not very confidential and secure, and the heating meter is easy to be maliciously modified. (3) The transmission wire is long, and the interference and signal attenuation are serious, requiring the addition of a drive circuit and an anti-interference circuit, which increases the cost. (4) When the heating meter is in operation, users cannot subjectively start or stop it, which does not reflect the principle of consumer freedom. (5) There is no temperature control function, so users cannot adjust the indoor temperature. (6) The main structure is a single channel type, which cannot realize the detection of return water (heating) flow, and cannot prevent users from maliciously stealing hot water, thus causing losses to the heating company. Based on the above, it was decided to independently develop an integrated dual-channel heating meter with more complete functions and more advanced technology. The structure is shown in Figure 2. Its expected functions are as follows: Encryption function: Automatically recognizes smart card passwords, which can prevent counterfeit cards or malicious channel attacks. Display function: Uses LCD liquid crystal display, which allows users to check the total amount of heating purchased, the remaining amount, the unit price, and the inlet and outlet temperatures at any time. Alarm function: When the remaining amount is less than the critical value, the valve will automatically close or open, and the alarm will be driven by sound and light, which can realize online monitoring. Shutdown function: Set up start and stop buttons for convenient user operation. No manual valve needs to be installed separately. Set up an electric lock switch so that users can manually cut off the power of the controller during the season when heating is not used, so that it is in a zero power consumption state. The valve will also automatically close when the remaining heat is zero or the system loses power. Data Settings: The system software allows for flexible settings of heating prices, alarm quantities, and overdraft amounts. Billing: Flexible monthly metering and billing of "fixed-amount heat" and "negotiated heat." Data Transmission: Data is transmitted via RFID cards for management; the computer system can transmit heating purchase information to the smart meter. Data Protection: Flash technology ensures secure real-time on-site data protection, preventing the loss of valuable data due to unforeseen circumstances. Power Monitoring: On-site monitoring of power supply anomalies and timely handling. Anti-theft Function: Simultaneous detection of inlet and outlet flow rates prevents energy theft. Intelligent Temperature Control: Users can set room temperature ranges according to their needs; the system automatically adjusts the room temperature through dynamic flow rate adjustment. 3. Overall Design 3.1 System Block Diagram This system is based on a microcontroller and mainly consists of flow sensing, temperature sensing, valve opening and closing control, a display module, an RFID module, power-off data saving, audible and visual alarms, and power monitoring. The hardware block diagram is shown in Figure 3. [align=center]Figure 3 Hardware Block Diagram[/align] 3.2 Module Description 3.2.1 Flow Sensor Installed on the pipeline system, used to measure the volume of water flowing through the heating circuit and send a flow signal. Currently, there are very few digital flow meters available on the market; most are mechanical, which cannot interface with our microcontroller. Later, we found that some new water meter flow detection systems on the market could be used as a reference. Therefore, the flow sensor in this design will be implemented using Hall effect devices. There are many Hall effect devices on the market, but most of them do not perform well in this system. We accidentally found the Hall effect IC—MLX90248 online. It can be said to be tailor-made for the design. 3.2.2 Temperature Sensor The temperature sensor is installed at the inlet and outlet of the pipeline system to collect the temperature of the medium in the system and send a temperature signal. DALLAS' latest single-wire digital temperature system DS18B20 is a new "one-wire device" that is smaller, has a wider applicable voltage range, and is more economical. The unique and economical features of the one-wire bus make it easy for us to build a sensor network. Its temperature measurement range is -55 to +125 degrees Celsius, and within the range of -10 to +85 degrees Celsius, the resolution accuracy can be programmed to be ±0.0625 degrees Celsius (9-12 bits). The on-site temperature is transmitted directly digitally via a "one-wire bus," greatly improving the system's anti-interference capability. It is suitable for temperature measurement in harsh environments. From a cost-performance perspective, it is sufficient to meet the design requirements. 3.2.3 RFID Card Reader/Write Module: This is the intermediate medium for data transmission. Choosing the appropriate storage medium as the key technology for this system's data transmission is crucial. Considering security, reliability, and economy, this system intends to use contactless RFID IC cards. The mainstream product in the world today—PHILIPS' MIFARE technology (with built-in MCU, ASIC, etc.)—has been established as an international standard: ISO/IEC 14443 TYPE A standard. If the password on the card is unknown beforehand, the possibility of guessing a sector on the card is almost zero, as the password can be extremely complex. This fully demonstrates the high security and confidentiality of the Mifare 1 card, as well as its versatility in various applications, making it a multi-purpose card (one-card-for-all). Currently, there are many mature read/write modules available on the market for design selection. Through comparison, the MCS-RC500 V3.3 contactless smart card universal reader/writer was chosen. The specific hardware circuit design is shown in Figure 4. Due to the rapid development of computer technology and the maturity of computer interface technology, the read/write modules available on the market are all computer communication-based devices. In conjunction with this design system, the necessary work now is to perform secondary development on the read/write module. That is, to use serial asynchronous communication technology to interface the reader module with the microcontroller. Writing the microcontroller interface assembly communication program is the key technology in this development. [align=center] Figure 4 Electrical Schematic Diagram of RF Card Reader[/align] 3.2.4 The integrator uses the AT89S51 as its core device, receives signals from the flow sensor and temperature sensor, processes, calculates, and displays the accumulated heat, accumulated flow, inlet water temperature, and return water temperature of the pipeline system. Simultaneously, it issues control commands. 3.2.5 The display module is used to display and facilitate customer inquiries about prepaid amounts, remaining heat, inlet and outlet temperatures, etc. 3.2.6 Valve opening/closing and alarm functions enable/disable user access and provide early warnings. 3.2.7 Power-off data saving ensures real-time data retention. A relatively mature system should possess reliable security measures. Imagine that after successfully recharging a user's machine with a prepaid card, the system continues to operate normally (without interruption). However, if the system loses power or resets for some reason (such as battery replacement), the real-time data running in the 89S51's internal RAM area will be lost. This will cause irreparable trouble for the company and users. Therefore, we added a power-off data saving circuit to this system. Since our data changes in real time, an online electrically erasable programmable memory (EEPROM) must be used. The design uses the AT24C02. The AT24C02 is a low-power CMOS serial EEPROM from Atmel Corporation, conforming to the I2C bus standard. It contains 256×8 bits of memory and features a wide operating voltage range (2.5～5.5V), a high number of erase/write cycles (greater than 10,000 times), and a fast write speed (less than 10ms). It is well-suited for embedding in this system. 3.2.8 Power Monitoring: On-site monitoring of power supply anomalies and timely handling. Ensuring stable and reliable operation of the microcontroller system is paramount, requiring stable power supply. This design uses the MAX706 chip as the main control unit for power management. It is a low-power CMOS chip with an operating current of only 100 microamps and includes a watchdog circuit. Using the MAX706 with simple peripheral circuitry, power switching and watchdog functions can be implemented. 4. Heat Energy Metering Principle: When hot water flows into a heat exchange system (radiator, pipes, etc.) at a certain temperature through the inlet pipe, the user gains heat through the heat exchange system while the hot water flows out at a lower temperature through the return pipe. The heat obtained by the user within a certain time period can be calculated by the following formula: Where: Q—Heat released or absorbed (J or wh); qm—Mass flow rate of water flowing through the heat meter (kg/h); qv—Volume flow rate of water flowing through the heat meter (m3/h); ρ—Density of water flowing through the heat meter (kg/m3); Δh—Enthalpy difference of water between the inlet and outlet temperatures of the heat exchange system (J/kg); τ—Time (h). [align=center]Figure 5 Table of water density and enthalpy[/align] The density and enthalpy of water can be determined by referring to national standards (as shown in Figure 5). When the temperature is not an integer, interpolation correction should be performed; once the structure of the table is determined, the volume flow rate of water can be obtained through experiments. 5. Technical Features Low power consumption: Adopts low-power and micro-power CMOS chip technology. High anti-interference: Adopts digital data processing technology, replacing the traditional easily interfered analog acquisition and transmission signals with highly anti-interference digital signals. High security: Data is encrypted and password protected. Utilizes PHILIPS' MIFARE technology. High precision: Employs multiple automatic compensation and correction methods. Versatility: Uses a multi-functional card, promoting the development of the Golden Card Project. Integration: Greatly reduces the possibility of energy theft. Dual-channel detection: Simultaneously detects the flow rate at the heating inlet and outlet to prevent energy theft. Intelligent temperature control: Users can set a room temperature range according to their needs, and the system automatically adjusts the room temperature through dynamic flow adjustment. 6. Conclusion This design, so far, is only a good start. It needs further improvement not only in technology and quality but also in product structure and variety. The development of heat meters is a technical guarantee for the sound reform of China's heating system, contributing to its reform. Main References [1] Wang Rong, Yuan Decheng, Xin Xiaoning et al. Research and Development of Intelligent Heat Meter [J]. Automation and Instrumentation, 2001, 16(2): 5-7 [2] Zhang Min. Research and Application Development of Core Technology of Contactless IC Card Smart (RF) Card and its Reading and Writing Device [EB/OL]. , 2001-01-10/2007-03-11 [3] Sun Ying, Zhang Jingmin, Zhang Zhijia et al. Design and Implementation of Mifare1 Card Reader Based on MFRC500 [J]. Microcomputer Information (Embedded and SOC), 2006, 22(2): 7-8 [4] Huang Jian. Research and Development of Intelligent Heating Meter System [D]. Hebei: Hebei University of Technology, 2004 [5] Xie Gang. DS18B20 Intelligent Temperature Controller [EB/OL]. , 2004-05-06/2007-03-10 [6] Lu Gongyu, Chen Xiong, Ni Bin, et al. Development and research of reader in radio frequency identification system [J]. Computer Engineering and Applications, 2006, 7: 89-91. About the author : Shao Feng (1981-), male, engineer, from Shangqiu, Henan Province, mainly engaged in automation teaching and research, and undertaking some scientific research projects and product development and design. Mobile: 13072662630 Email: [email protected] Address: Automation Teaching and Research Office, Department of Mechanical and Electrical Engineering, Henan University of Science and Technology, Xinxiang City, Henan Province Postcode: 453003 Note: This design project is a project of the Henan Provincial Higher Education Young Backbone Teachers Funding Program.