【正文】 any way: if it does not light up, reverse the test leads. The LED will now light up. The anode of the LED is that which is connected to the “A” terminal (positive pole of the battery). This method is safe, as reverse voltage can never exceed 3 volts in this test. ELECTRICAL CHARACTERISTICS OF LEDS: Electrically, a LED is similar to the conventional diode in that it has relatively low forward voltage threshold. Once this is exceeded the junction has a low slope resistance and conducts current readily. An external resistor must limit this current. Forward voltage drew across red LED is nominally V but spread with mercial diodes, it may be as high as 2 volts or so, while the Green LED drops . This difference accounts for use of lower limiting resistor used with the Green LED. Another important parameter of the LED is its maximum reverse voltage rating. For typical Red device it is of the order of 3 volts. But for Green LED it is somewhat higher 5 to 10 volts. The LED produces light only when a . current is passed in the forward direction and the amount of light emitted by a LED is proportional to the forward current over a broad range. It means that light intensity increases in an approximately linear manner with increasing current. CIRCUIT DIGRAM: 8051 PORT 1 PORT 3 TRAFFIC DENSITY SENSOR Port 2 8051 take cares of the timer for the signal according to the density of the traffic sensed by multiple sensors on road. As shown in the circuit a microcontroller is programmed to automatically “ON” and “OFF” the LEDs (traffic light). The crystal oscillator is provides the necessary clocking for the mocrocontroller to work properly. The four traffic lights, shown as 4 groups of 3 LEDs (Red, Green, Yellow), is actually installed at each of the four roads. The necessary stabilized power source is designed by the use of LM7805, as shown above (in the lower figure). The whole circuit will be implemented on a zero PCB. The programming of the Microcontroller can be done either in C or in Assembly, using a programmer. References： [1] G. L. Guthrie,“ Sensitive ac Hall Effect Circuit” Review of Scientific Instruments, Issue 8. pp. 1177 – 1179,1965. [2] Z. Fuqiang, Y. Bo, and C. Yitao, “ Traffic light control for a single intersection based on wireless sensor work,” Electronic Measurement amp。隨著半導(dǎo)體技術(shù)的進步，一個 穩(wěn)步 上升的創(chuàng)新 平臺 在 基于 嵌入式 技術(shù) 變化 交通燈控制的 工程已 逐步形成 。 簡要介紹了 8051單片機 ： 當(dāng)我們了解一個新電腦我們熟悉的機器能力我們使用，我們可以通過學(xué)習(xí)內(nèi)部硬件設(shè)計（設(shè)備架構(gòu)），同時也了解的規(guī)模，數(shù)量和大小的寄存器。下圖描述了一個普通的微控制器框圖。結(jié)合靈活的 8位處理器的系統(tǒng)內(nèi)可編程閃存在單片芯片，該公司的 AT89S 52是一個功能強大的微控制器提供了一個高度靈活和成本效益的解決方案的許多嵌入式控制應(yīng)用。在掉電模式節(jié)省內(nèi)存內(nèi)容但凍結(jié)振蕩器，禁用所有其他芯片的功能，直到下一個中斷。在這個項目中我們使用外部交流電源（ 220）作為輸入，高電壓轉(zhuǎn)換成 12伏交流的降壓變壓器，然后我們使用電壓調(diào)節(jié)器和過濾器的橋式整流器轉(zhuǎn)換成直流電壓的交流。外部效率在室 溫下通常是百分之5。在硅摻雜砷化鎵二極管，發(fā)光峰移到。一個關(guān)鍵問題，用發(fā)光二極管的光纖光學(xué)耦合光從半導(dǎo)體的纖維。后來，硅類型可用較低的漏電流和光敏感度。 可控硅與一個窗口也可，稱為激光，這是非常敏感的，可以打開和關(guān)閉電源，以光。由于光源（發(fā)光二極管）和光電二極管的身體保持分離（以毫米）包中，分離到表就可以了。這中間輸入?yún)^(qū)域是一個 死區(qū) 里面沒有任何回應(yīng)，財產(chǎn)稱為滯后，這就像是在機械聯(lián)動。有紅外線發(fā)射發(fā)光二極管發(fā)出可見光。圓頂發(fā)光二極管作為一個鏡頭的光漫射器。它類似于傳統(tǒng)的整流二極管符號與箭頭指出。有時，陰極側(cè)有一個單位的基礎(chǔ)。當(dāng)這發(fā)生陽極引線連接 的負(fù)面測試引線與陰極的積極測試導(dǎo)線的電阻。該電阻限制了二極管的電流的帶領(lǐng)下，以一個安全值測試。這種方法是安全的，當(dāng)反向電壓不能超過 3伏特，在這個測試。畫在紅色發(fā)光二極管正向電壓 ，名義上是傳播商業(yè)二極管，它可能高達 2伏左右，而綠色滴板。但對于綠色發(fā)光二極管是較高的 5至 10伏特。晶體振蕩器提供必要的時鐘的 微機 正常工作。微控制器編程的可以是在或在裝配，使用程序員。 必要的穩(wěn)定電源的目的是通過使用 lm7805，如上所示（在較低的數(shù)字）。這意味著光的強度增加了大約線性的方式增加電流。 另一個重要的參數(shù)的發(fā)光二極管是其最大反向電壓等級。一旦這是超過交界處有一個低阻力和傳導(dǎo)電流容易。發(fā)光二極管將發(fā)光。 另一個安全的方法是連接測試電路如圖 2所示。一個簡單的板凳的方法是使用歐姆表納入 3伏歐姆表的功能細(xì)胞。 發(fā)光二極管往往導(dǎo)致不同的長度和較短的一個是陰極。實際的直徑略有不同的是。一個正常的發(fā)光二極管發(fā)出的電流消耗在板和馬。 如果高靈敏度是 必要的滯后是一個問題，但在許多電路，