An intelligent meter reading system based on wireless communication and public telephone network

4 System Hardware Electrical Principles

4.1 Electrical Principles of Water Meter Transmitter

The function of the water meter transmitter is to transmit the water consumption measured by the water meter to the data processor by wireless communication. The block diagram is shown in Figure 3. The Hall sensor installed in the water meter is used to detect the water consumption. For every 0.1t of water flowing through the water meter, the Hall sensor sends a pulse signal, which generates a red 1s wide pulse through the series steady-state circuit, and then is shaped by the Schmidt inverter 4069 and sent to the encoder PT2262 for encoding. The PT2262 full code address is 4 11. The encoded data is sent to the wireless transmission module for transmission. The radio transmission frequency is 400MHz and the effective distance is 50m. At the same time, the transmitter also has some additional functions.
(1) Anti-theft function. Due to the characteristics of dry water meters relying on electromagnetic transmission, they are easily affected by external magnetic fields. If the user places a strong magnet near the water meter, it will reduce the speed of the water meter transmission gear and reduce the measurement accuracy of the water meter. The transmitter is also equipped with a Hall sensor dedicated to measuring magnetic field strength. When a strong magnetic field is detected near the water meter, the Hall sensor sends an alarm pulse, which is wirelessly transmitted to the data processor through the transmitter.
(2) Backup battery. To ensure that the transmitter can work normally during a power outage, while the AC 220V power supply is provided, there is also a 4.8V nickel-hydrogen battery and a battery voltage monitoring and charging circuit composed of LM358 and 555 to enable the battery to be charged normally. The backup battery can maintain the transmitter's continuous operation for 48 hours.

4.2 Principle of the electrical part of the data processor

The data processor is the key equipment of this system. It consists of a wireless receiving and decoding part, a clock calendar, 8051 and peripherals, a telephone transceiver circuit, a power supply, etc. The block diagram is shown in Figure 4. The wireless receiving module and the transmitting module work at the same frequency of 400MHz; decoding is completed by PT2272, the working frequency is the same as PT2262, and the address code is consistent with PT2262. The clock calendar chip DALLAS12887 provides the system with an accurate 100-year clock calendar, including year, month, day, hour, minute, second, week and timing alarm signal.

The telephone receiving and transmitting routing dialing circuit and audio decoding circuit are composed. The 4-16 decoding wife MC4514 analog switch 4066 forms a 3*4 virtual keyboard array. The 8051 controls the opening and closing of the keys to complete the encoding of the telephone number to be dialed and the uploaded data, and sends the telephone number and data to the dialing circuit. The dial-up dedicated chip is W91312, and the crystal frequency is 3.58MH. After receiving the telephone number from the management computer, it will be dialed immediately. When the handshake signals at both ends are completed and the line is confirmed to be connected, the 8051 controls the uploaded data to be output to the management computer in audio mode; the function of the audio decoding circuit is to decode the audio signal and output it in the form of BCD code. When the data processor dials the management computer, the management computer replies with a connection handshake signal. The signal is an audio signal. After being amplified by the AC amplifier circuit, it is sent to the audio decoding chip MC145436 for decoding, and finally sent to 8051 in the form of BCD code.

The system is powered by 220V AC and lithium backup battery. When the residential power outage or artificial power outage occurs, the system can still maintain normal operation for 48 hours.

4.3 Principle of the electrical part of the management computer communication interface board The

management computer communication interface board consists of a dialing circuit, an audio decoding circuit, a telephone ringing detection circuit, a photoelectric isolation circuit and a power supply circuit, as shown in Figure 5. The dialing circuit and audio decoding circuit are the same as those on the digital processor board.

5 System software

This system software consists of three parts: data receiving, data conversion and charging system.

(1) Data receiving system. Since it is necessary to read the user's water consumption from the parallel port, the data receiving system will convert the user's data into a text file after the user's water consumption is up. This system starts automatically after the operating system starts and is always in working condition.
(2) Data conversion system. Considering that the data after receiving is a text file and cannot be directly entered into the database, a data conversion system is designed to store the data into the database. This system starts automatically after the operating system starts and is always in working condition.
(3) Charging system. After the legitimate user logs in to this system, daily business processing is carried out. According to the user's computer configuration, the system can run in a stand-alone environment or in a network environment.

The requirements for computer software and hardware in the stand-alone operating environment are: the operating system is WIN95/WIN98; the database is Oracle734.

The network operating environment has the following requirements for computer software and hardware: the client of the operating system is WIN95/WIN98, and the server is WIN2000/WINNT;

the client of the database is Oracle734; the server is Oracle8i;

the hard disk is 5G; 

water, as a limited resource, is increasingly valued by people. Saving water is no longer an initiative, but our responsibility and obligation. Therefore, it is very urgent to accurately measure the water used by residents, enterprises and institutions. One valve per household and one meter per household are the general trend. On the other hand, with the implementation of the one-household-one-meter project, the difficulty of measuring and charging for residents' water use has gradually increased. In order to effectively solve the many drawbacks of household meter reading, improve efficiency, avoid public security problems caused by household meter reading, and prevent arrears of fees. Therefore, it is imperative to replace traditional household meter reading with outdoor intelligent meter reading.

Among the existing intelligent meter reading systems, some are realized through power line carrier network, and some are realized through laying dedicated lines. Comparing the two intelligent meter reading systems, the power line carrier network has relatively large limitations, mainly due to the limitation of transformers; the construction project is relatively large and the transformation cost is relatively high when the dedicated line is laid. Therefore, the use of the public telephone network to realize the intelligent meter reading system avoids the above-mentioned unfavorable factors, has a wide range of applications, is easy to install, does not require laying lines, and has relatively low transformation costs, which brings a lot of convenience to users. Therefore, the application prospects are very broad.