Development of digital transmission and voice intelligent recognizer in centralized meter reading system

    Abstract: Based on the analysis of the structural characteristics of the centralized stopwatch system, combined with the actual situation of the centralized stopwatch system, the article introduces the main functions of the newly developed digital transmission and voice intelligent recognizer, and gives the data transmission and voice intelligent recognizer. The software and hardware design scheme and system working process of the recognizer device.

    Keywords: DTMF recognition centralized meter reading microcontroller

With the continuous development of our country's economic construction and the continuous improvement of residents' living standards, residents' demand for electricity has also increased significantly. According to this electricity consumption situation and the modern requirements of electricity management, the power supply department has determined the requirements for urban and rural residents' daily life. Electricity counting and electricity bill collection have gradually been completed using a combination of advanced computers and communication technologies, that is, electronic centralized meter reading is used to replace the manual meter reading that previously required a large number of meter readers to go door-to-door to read and collect electricity bills. method, thus greatly improving work efficiency and having the advantages of fast, reliable and accurate.

1 Centralized meter reading system structure

The system structure commonly used in centralized copying systems is shown in Figure 1. The system is mainly composed of the terminal meter data collection module installed on the home side, the data concentrator installed on the distribution transformer side, and the computer system of the electricity charging management center.

Communication between the electricity charging center and the concentrator can be carried out by wireless, wired (telephone lines), high-voltage carrier, etc. The wired method uses the existing telephone switching network. This method only requires the connection between the concentrator and the concentrator. Installing a Modem in the toll center can complete the two-way transmission of data, and has the advantages of easy installation, reliable channel, and high data transmission rate, so it has broad application prospects.

2 Disadvantages of telephone network centralized meter reading system

There is a shortcoming in using the existing telephone network as a transmission channel for meter reading data: it is necessary to install a dedicated telephone for meter reading communication, which will add many additional costs (initial TV installation fee, monthly basic fee etc.), and this is obviously a waste of resources; if you use the originally installed telephone, you can save telephone charges, but because the telephone is not a dedicated telephone, when the charging center communicates with the concentrator to read meters, it will not be established before communication is established. , to make a call to the concentrator, the user's phone will also ring. If the user picks up the phone, it may interfere with the normal meter reading communication; and if other personnel want to call the user at the distribution transformer, the centralized The device may automatically go off-hook, thus affecting the normal use of the user's phone. How to coordinate and resolve this contradiction? After analyzing the signal flow between the switch and the user's phone during the normal call connection process, the author designed a set of intelligent switching devices that can automatically distinguish the data transmission of the charging management center from the general voice calls. This is a good way to The above contradiction is solved, and it is successfully applied in the low-voltage power carrier centralized meter reading system.

3 Main functions of digital transmission/speech recognizer

Figure 2 shows the functional block diagram of the data transmission/speech recognition device. The identifier device mainly consists of DTMF recognition, line interface, ring current circuit, switch array and MPU.

(1) DTMF identification is mainly used to complete the DTMF signal detection after the line is connected, and provide the MPU with information to identify data transmission and calls, so that the MPU can perform different processing operations;

(2) The line interface is used to complete the connection between the identifier and the telephone outside line, including ring detection, off-hook and on-hook functions;

(3) The ring current circuit is used to provide ringing signals to the concentrator and user phones;

(4) The switch array is composed of relays, which are used to connect the concentrator and user phones, and determine the on and off of the switch under the control of the MPU;

(5) The task of the MPU is to sample various parts of the microcontroller control circuit and complete tasks including off-hook, on-hook, ringing and off-hook detection based on the signals sent from each part.

The MPU in the digital transmission/speech recognition device can use the AT89C2051 microcontroller produced by Atmel Company. It contains 2k of program memory and 16 I/O lines, which can meet the needs of controlling signal acquisition;

The DTMF identification circuit is mainly composed of the MT8870 chip as the central component. This chip has the advantages of simple peripheral circuits and high reliability.

4 Main working processes of the system

4.1 Incoming external phone calls

When an external call comes in and the line interface in the system detects a 70V, 25Hz ring signal, the system can convert this signal into a DC signal S0. When the MPU detects a valid S0, it controls the signal S1 to cause the line interface to Connect the outside line in the form of a dummy load, the external switch stops sending ring current, and the line is connected; if it is a data transmission call, the computer at the charging center will add a DTMF signal after dialing the corresponding phone number; MPU turns on 5 After the second timer, the DTMF recognition part is allowed to work, and within this time it is detected whether there is a DTMF signal to detect the S5 indication.

If a valid S5 is detected within the specified timing time, it is judged that the call is a data transmission, and then the concentrator is connected through the S4 control switch network and the ringing circuit is connected to send the ringing signal to the concentrator and send back at the same time The caller waits for a single tone; then continuously detects S2, waits for the concentrator to complete communication, and then hangs up. If the concentrator still does not pick up the phone after sending ring signals to the concentrator 6 times, the system automatically restores each part of the circuit and waits again. One call.

If no valid S5 is detected within the specified timing time, the call is judged to be a normal call, and then the user's phone is connected through the S4 control switch network, the ringing circuit is connected, and a ringing signal is sent to the user's phone. At the same time, the caller's waiting tone is sent back; and then S2 is continuously detected, waiting for the user's phone to hang up after the call is completed. If the user's phone still does not pick up the phone after sending the ring times to the user's phone, the system will automatically restore all parts of the circuit and wait for the next time. call.

Since the user's phone and the concentrator are usually not directly connected to the outside line, but are connected to the outside line through the switch network under the control of the MPU, the ring current sent from the outside line and the ring current generated by the recognizer itself will not cause the concentrator and user phone to Ring at the same time, thus avoiding mutual interference between data transmission and calls.

4.2 Use of user phones on the distribution transformer side for calls

The main task of the MPU is to monitor external calls and internal outgoing calls. When it detects a valid S3 user off-hook signal, it connects the user's phone to the external line through the S4 control switch network so that the user can hear the switch sending After that, the MPU starts to detect S2 until the user hangs up. If S2 is valid, the MPU will restore various parts of the circuit to wait for the next cycle of detecting incoming and outgoing calls.

5 Conclusion

This data transmission/call intelligent identifier makes full use of the advanced MPU program real-time control function, and has a simple circuit, flexible programming, and low cost. It uses the existing telephone network to transmit meter reading data without affecting the user. The normal use of telephones does not cause interference, and it makes full use of existing telephone channel resources and saves user fees. Therefore, it is foreseeable that this data transmission/communication intelligent identifier will be widely used in centralized meter reading systems.