【正文】 of munication between the central station and the fire department(e) Availability of emergency power supply. The codes usually also specify the types and frequency of tests for all equipment.A fire detection and alarm system is a bination of devices designed to signal an alarm in case of a fire. The system may also acplish fan control, fire door hold or release, elevator recall, emergency lighting control and other emergency functions. These additional functions supplement the basic system which consists of detection and alarm devices and central control unit. Technology has an influence on system architecture. When technology changes, the architecture has to be revised to take advantage of these changes. In recent years, VLSI technology has been advancing at an exponential rate. First NMOS and, in the last year or two, CMOS chips have been produced with the same packing density with more gates per chip yet at a lower power consumption than NMOS. Surely this change in technology must affect our design of hardware at both the chip and the system level. At the chip level, single chips are now being produced which are equivalent to board levels of only the previous year or two. These chips have microprocessor, memory in RAM and ROM, IO Ports both serial and parallel, A/D timer, flags and other functions on chip. At the system level, the new chips make new architectures possible. The objective of this paper is to show how technology can influence system architecture in the field of fire control. The new high density single chip microcontrollers are incorporated in the design of a large scale system and yet we obtain a smaller system with a better performance. In terms of fire detection and alarm monitoring, this is reflected directly in the local station hardware, because of their remoteness and power supply requirements. A plete local station can be designed around a single CMOS chip with power consumption of a few m W depending on system operation. This approach reduces the cost and plexity of design, implementation and maintenance and provides easily expandable and portable design. This implementation was not possible with old technology. Most of fire detection/monitoring systems available are tailored towards a specific application and lack the use of recent advances in CMOS VLSI technology. In this study, we develop a fire detection/monitoring system which is general in concept, readily implementable in a multitude of applications for early detection of a fire before it bees critical, for equipment and evacuation of personnel. Here, we propose a central control and distributed control/detection/monitoring with adequate munication, where use is made of singlechip microcontrollers in the local stations, thus improving controllability and observability of the monitoring process.2 Detection and alarm devicesA basic fire detection system consists of two parts, detection and annunciation. An automatic detection device, such as a heat, smoke or flame detector, ultraviolet or infrared detectors or flame flicker, is based on detecting the byproduct of a bustion. Smoke detectors, of both ionization and optical types, are the most monly used detector devices. When a typical detector of this type enters the alarm state its current consumption increases from the pA to the mA range (say, from a mere 15pA in the dormant mode to 60 mA) in the active mode. Inmany detectors the detector output voltage is well defined under various operating conditions, such as thosegiven in Table 1:Table 1 Typical detector voltage output levelsvoltage levelDetector condition22VDetector is in open circuit condition13V~22Vdetector is normal1V~13Vdetector is in an alarm state1Vdetector is in short circuit conditionThe more sensitive the detector, the more susceptible it is to false alarms. In order to control the detector precisely, either of the following methods is used: a coincidence technique can be built into the detector, or a filtering technique such that a logic circuit bees active only if x alarms are detected within a time period T. The detection technique depends greatly on the location and plant being protected。語(yǔ)音報(bào)警中的退耦電容可以改變音質(zhì)。經(jīng)實(shí)驗(yàn)的標(biāo)定，：濃度（%LEL）濃度誤差濃度（%LEL）濃度誤差0050553553101600154652203703251755305802353854402903455955%，在所規(guī)定誤差范圍177。MQ2為煙霧傳感器，電路采用交流供電，220V交流市電從插頭引入電路，經(jīng)電源變壓器降壓后變?yōu)橹绷?，直流電壓直接供傳感器MQ2的加熱絲hh工作，加熱絲給傳感器MQ2預(yù)熱一定時(shí)間后，才能正常檢測(cè)煙霧。(5)用示波器檢測(cè)振蕩電路，主要是檢測(cè)119引腳。(2) 用萬(wàn)用表檢測(cè)31引腳是否有5V電壓。如果經(jīng)檢測(cè)沒(méi)有問(wèn)題可以工作，就可以在焊接板上開始對(duì)元器件進(jìn)行焊接。(4) 仿真運(yùn)行，“debug”—“execute”。（由于語(yǔ)音芯片、煙霧傳感器以及風(fēng)扇等元器件在Proteus元器件庫(kù)中沒(méi)有收錄，此次仿真過(guò)程中用電位器表示煙霧傳感器，用蜂鳴器表示語(yǔ)音報(bào)警，用發(fā)光二極管代表風(fēng)扇。Proteus是世界上著名的EDA工具(仿真軟件)，從原理圖布圖、代碼調(diào)試到單片機(jī)與外圍電路協(xié)同仿真，一鍵切換到PCB設(shè)計(jì)，真正實(shí)現(xiàn)了從概念到產(chǎn)品的完整設(shè)計(jì)。最后通過(guò)progisp把編譯、調(diào)試正確的程序下載到AT89S51芯片中。編譯前要進(jìn)行一個(gè)重要的操作。彈出一個(gè)框，選擇“否”。 程序編譯及調(diào)試界面編譯及調(diào)試具體的步驟首先打開Keil uVision。 jidianqi=1。} void main() //主函數(shù){ yanwu=1。x0。 sbit yuyin=P1^1。程序初始化結(jié)束后，系統(tǒng)進(jìn)入監(jiān)控狀態(tài)。二極管D2的作用是保護(hù)繼電器。繼電器中開關(guān)動(dòng)作受三極管控制，當(dāng)三極管處于飽和導(dǎo)通狀態(tài)時(shí)，集電極電流驅(qū)動(dòng)繼電器動(dòng)作，開關(guān)閉合，電機(jī)回路導(dǎo)通，電機(jī)開始工作。減小該電容值，可使噪聲能量沖擊的幅度變小、寬度變窄；故選用10uF/。芯片穩(wěn)定工作后，BYPASS的電壓值約為VCC的一半，改變BYPASS外接電容的容值大小，可以有效抑制噪聲。通過(guò)接在1管腳和8管腳間接電解電容（1腳接電容+極）來(lái)改變?cè)鲆?，斷開時(shí)增益為20。為使外圍元件最少，電壓增益內(nèi)置為20。在直通模式下，直通開關(guān)閉合，對(duì)話筒說(shuō)話會(huì)從喇叭里擴(kuò)音播放出來(lái)，構(gòu)成喊話器功能，由于該模式下的話筒放大同時(shí)經(jīng)過(guò)AGC自動(dòng)增益調(diào)節(jié)和帶通濾波器，其音質(zhì)比通常的話筒放大器要好很多，而且不會(huì)出現(xiàn)喇叭過(guò)載的情況。平時(shí)FT端為低，要實(shí)現(xiàn)直通功能，需將FT端接高電平，同時(shí)REC、PLAYE和PLAYL保持低。單端使用必須在輸出端和喇叭之間接耦合電容，而雙端輸出既不用電容又能將功率提高至4倍。話筒參考(MIC REF)：此端是前置放大器的反向輸入。話筒輸入(MIC)：此端連至片內(nèi)前置放大器。持續(xù)至此端回到低電平，或遇到EOM標(biāo)志，或內(nèi)存結(jié)束，放音結(jié)束后自動(dòng)進(jìn)入節(jié)電狀態(tài)。邊沿觸發(fā)放音(PLAYE)：當(dāng)此管腳有一個(gè)上升沿時(shí)，可以驅(qū)動(dòng)芯片開始進(jìn)行放音。錄音 (REC)：REC高電平有效，不管芯片處在節(jié)電狀態(tài)還是正在放音的狀態(tài)只要REC變?yōu)楦唠娖剑酒烷_始錄音。電源線的匯合這樣接法會(huì)使得噪聲的影響減少到最小。語(yǔ)音報(bào)警電路中采用的語(yǔ)音芯片為ISD1820PY。一個(gè)完整的煙霧傳感器都必須具備：(a)能夠檢測(cè)某種單一煙霧，而對(duì)共存的其它煙霧不響應(yīng)或低響應(yīng)； (b)對(duì)被測(cè)煙霧具有較高的靈敏度，能有效地檢測(cè)允許范圍內(nèi)的煙霧濃度；(c)對(duì)檢測(cè)信號(hào)響應(yīng)速度快，重復(fù)性好；(d)長(zhǎng)期工作穩(wěn)定性好，制造成本低，使用與維護(hù)方便等條件。一般情況下，傳感器輸出的信號(hào)會(huì)比較弱，而且其中還包括了一些避免不了的干擾，對(duì)這種信號(hào)的放大就需要有很好的共模抑制比以及高增益、低噪聲和高輸入阻抗的放大電路。(7)適宜于煙霧、液化氣、丁烷、丙烷、甲烷、酒精、氫氣等的探測(cè)。(2)雙路信號(hào)輸出（模擬量輸出及TTL電平輸出）(3)TTL輸出有效信號(hào)為低電平。它是利用氣體在半導(dǎo)體表面的氧化和還原反應(yīng)導(dǎo)致敏感元件阻值變化。此次使用的氣敏式煙霧傳感器選擇的具體型號(hào)