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   Abstract: Introduced that one kind (Public Switch Telecommunication Network) as the transmission medium residential district seeks help urgently take public telephone network PSTN the system. The system take the monolithic integrated circuit as a core, (DTMF, Dual Tone Multiple Frequency) takes the mailing address by the double sound multi-frequencies. This system the inhabitant provides for the plot in seeks help urgently the service, has the reliability to be high, the cost low, easy to popularize and so on merits. In the article gives the system schematic diagram, the main hardware circuit and the flow chart. Finally has carried on the forecast to this system’s application prospect.

    Key word: PSTN monolithic integrated circuit double sound multi-frequency emergency call

Introduction

Along with the people living standard’s unceasing enhancement, the family safe service is bringing to people’s attention gradually. Because sub-woman’s going to work, many old people the getting sick patient cannot obtain the very good attendance particularly, has when the dangerous situation cannot obtain the stitch in time, the existence very big safe hidden danger. Therefore, establishes the networking in the residential district to seek help urgently the system, enables the plot estate management center to carry on the stitch in time to inhabitant’s dangerous situation, this is precisely the people hoped. Along with telephone equipment’s large-scale popularization, causes the use public telephone network to realize seeks help becomes urgently easy and feasible. Here, this article will introduce that one kind seeks help urgently based on the public telephone network’s society the system, by now improved the human to occupy the environment and to realize the building automation to have the big help.

1 system principle of work

This system take the monolithic integrated circuit as a core, by DTMF the digit dialing electric circuit, the remote control launch and the accepting circuit, the telephone number storage circuit and exempts raises the speech circuit four parts to be composed. When has the dangerous situation occurs, presses down on the callmaker or remote control’s emergency button, after the monolithic integrated circuit examines this signal, will save the circuit number transmits, after the connection, may realize raises to says. In addition, because in this system’s telephone number is the memory, in a piece brings I2C in the bus interface E2PROM chip, therefore this number may momentarily revise, is extremely convenient. System principle diagram as shown in Figure 1.

Figure 2

2 main hardware circuits

2.1 DTMF digit dialing chip and monolithic integrated circuit’s connection principle

Double sound multi-frequency signal (DTMF), usually Jian Chengwei double tonic train signaling. It is with two specific tone signal combination superimposition, represents some digit or the mark. Two tone’s frequencies are different, represents the digit or the function are also different. In the double sound multi-frequency telephone, has 16 pressed keys, 10 integer keys (0~9), 6 functional keys (*, #, A, B, C, D). Thus, according to the combination principle, it must have 8 kind of different single tonic train signalings. The double voice-frequency dialing’s group frequency which (international telegram telephone Inquiry board) proposed according to CCITT suggested that internationally uses 4 low frequency frequencies (697Hz, 770Hs, 852H2, 941Hz) and 4 high frequency frequencies (1209Hz, 1336Hz, 1477Hz, 1633Hz) extracts one kind of frequency to carry on the combination willfully, altogether has 16 different combination ways, represents 16 kind of different digit or the mark, as shown in Table 1.

Table 1 pair of sound multi-frequency digit dialing code

In this system, the double sound multi-frequency signal produces by DTMF signal generating device special-purpose chip UM95087. Its input end R1~R4 (line), C1~C4 (row) already may meet the ordinary call keyboard, may also use in the level input. The input two tonic train signaling linearly is folded puts together, the DTMF signal which produces by the UM95087 16 feet outputs. A tonic train signaling designated by input end R1~R4 from the low frequency group that another tonic train signaling designated by input end C1~C4 from the high frequency group. When decides (Ri) inputs for the low level, chooses in its low frequency group; When the row (Ci) inputs for the level, chooses in its high frequency group. The output audio frequency tone scope is 400~500mV, the double audio frequency output’s harmonic distortion chord frequency distortion is smaller than 10%, the frequency error is ±10%, the accuracy is smaller than 0.75%, high frequency compared to low frequency aggravates 2dB. The UM95087 15 feet use for to prevent the tone production, when for low level, the output will not have the tone output; 10 feet are the static chirp out-ports; 2 feet for transmitter stop-go control end; 7 feet are the internal oscillator input ends; 8 feet are the internal oscillator out-ports. When application, turns on the 3.57954MHz crystal oscillator between the 7th foot and the 8th foot then. Presently uses monolithic integrated circuit AT89C51 to control DTMF generator UM95087 to realize the channel coding, its interface circuit like 2 show.

    According to double tonic train signaling (DTMF) the combination principle and the above interface circuit, may result in the DTMF signal and the binary system coded signal corresponding relationships, as shown in Table 2.

Table 2 DTMF signals and binary code corresponding relationships

2.2 exempt raises the speech circuit

Exempts raises the speech circuit to request to achieve the sound to be clear, to be loud and clear, not because of the words, the message, but will disturb mutually. Therefore, to exempts puts forward speech circuit’s specification to be high, puts words in somebody’s mouth the amplifier sensitivity to be high; Must be big the words amplifier output; Can suppress the side sound effect which effectively is caused the words. This system uses special-purpose exempts raises telephone conversation chip MC34018 to constitute exempts raises the speech circuit.MC34018 is one kind of application widespread, high grade exempts raises the telephone conversation integration chip, it uses the voice control way half-duplex to exempt raises the telephone conversation, contains has the transmit amplifier, the speaker power amplifier, the weaken control system, the background noise supervisory system, the transmission and the receive attentuator. Its weaken control system not only receives the corresponding message with the words level control, also receives the background-noise level control. Exempts by the MC34018 constitution proposes speech circuit as shown in Figure 3.

3 system software designs

The software design seeks help signal gathering including the monolithic integrated circuit, the circuit number read and the transmission, the telephone number establishment and so on three parts. And, telephone number’s read and the establishment are the software design key points. Because the telephone number saves, in a piece brings in I2C connection E2PROM, but this system uses the monolithic integrated circuit does not have the I2C connection, therefore simulates the I2C main line’s succession through the software. On the monolithic integrated circuit, expands one to simulate the I2C bus interface to realize between the monolithic integrated circuit and the E2PROM chip correspondence.

After the monolithic integrated circuit completes the replacement and the initialization, when has seeks help the signal input, the monolithic integrated circuit will save the telephone number takes out gives the UM95087 chip concurrently, causes the telephone connection, completes the telephone conversation to speak the function. Its procedure flow frame as shown in Figure 4.

Conclusion

In recent years, our country was getting bigger and bigger to the residential district construction’s investment efforts. Take 1999 as the example, the country to the residential district total investment is 1700 ~ 180,000,000,000 Yuan. According to the ministry of construction to the residential district reality, the medium and high three rank’s division, the plot intelligence changes into the residential district total investment 1%~3%. By this proportion computation, the only 1999 year amounted to 17 ~ 5,400,000,000 Yuan to the plot intellectualization’s demand. But is unceasingly thorough along with the housing organizational reform as well as the people the unceasing enhancement which asks to the housing environment end, this value large scale will also enhance.

This article states the community to seek help the system to have the strong usability, the cost to be inexpensive, the promotion is convenient, already through comprehensive experiment and place in operation. The residential district will seek help the system to promote unceasingly urgently will certainly brings the positive influence to the intelligent building system’s construction and the development and the people living standard enhancement.