LED 一般是恒流操作的，如何改變 LED 的亮度呢？答案就是 PWM 控制。在一定的 頻率的方波中，調整高電平和低電平的占空比，即可實現。比如我們用低電平點亮一個 LED 燈，我們假設把一個頻率周期分為 10 個時間等份，如果方波中的高低電平占空比是 9：1， 這是就是一個比較暗的亮度，如果方波中高低電平占空比是 10：0，這時，全部是高電平， 燈是滅的。如果占空比是 5：5，就是一個中間亮度，如果高低比是 1：9，是一個比較亮的 亮度，如果高低是 0：10，這時全部是低電平，就是最亮的。 實際上應用中，電視屏幕墻中的幾十百萬 LED 象素都是這樣控制的，而且每一個象素 都有紅綠藍 3 個 LED，每個 LED 可以變化的亮度是幾百到幾萬或者更多的級別，以實現真 彩色的顯示。還有在您的手機中，背光燈的亮度如果是可以變化的，也應該是這種工作方式。 目前的城市彩燈也有很多都使用了 LED，需要控制亮度是也是 PWM 控制。 下面來分析我們的例程，在這個例程中，我們將定時器 2 溢出定為 1/1200 秒。每 10 次脈沖輸出一個 120HZ 頻率。這每 10 次脈沖再用來控制高低電平的 10 個比值。這樣，在 每個 1/120 秒的方波周期中，我們都可以改變方波的輸出占空比，從而控制 LED 燈的 10 個 級別的亮度。 為什么輸出方波的頻率要 120HZ 這么高？因為如果頻率太低，人眼就會看到閃爍感 覺。一般起碼要在 60HZ 以上才感覺好點，120HZ 就基本上看不到閃爍，只能看到亮度的變 化了。 下面請看程序，程序中有比較多的注釋： ――――――――――――――――――――――― #define uchar unsigned char //定義一下方便使用 #define uint unsigned int #define ulong unsigned long #include <reg52.h> //包括一個 52 標準內核的頭文件 sbit P10 = P1^0; //要控制的 LED 燈 sbit K1= P3^2; //按鍵 K1 uchar scale;//用于保存占空比的輸出 0 的時間份額,總共 10 份 char code dx516[3] _at_ 0x003b;//這是為了仿真設置的 //模擬 PWM 輸出控制燈的 10 個亮度級別 void main(void) // 主程序 { uint n; RCAP2H =0xF3; //賦 T2 的預置值，溢出 1 次是 1/1200 秒鐘 RCAP2L =0x98; TR2=1; //啟動定時器 ET2=1; //打開定時器 2 中斷 EA=1; //打開總中斷 while(1) //程序循環 { ;//主程序在這里就不斷自循環，實際應用中，這里是做主要工作 for(n=0;n<50000;n++); //每過一會兒就自動加一個檔次的亮度 scale++; if(scale==10)scale=0; } } //1/1200 秒定時器 2 中斷 timer2() interrupt 5 { static uchar tt; //tt 用來保存當前時間在一秒中的比例位置 TF2=0; tt++; if(tt==10) //每 1/120 秒整開始輸出低電平 { tt=0; if(scale!=0) //這里加這一句是為了消除滅燈狀態產生的鬼影 P10=0; } if(scale==tt) //按照當前占空比切換輸出高電平 P10=1; } ―――――――――――――――――― 在主程序中，每延時一段時間，就自動換一個占空比，以使亮度自動變化，方便觀察。 編譯，運行，看結果。 可以看到，LED 的亮度以每種亮度 1 秒左右不斷變化，共有 10 個級別。
上傳時間： 2017-11-06
上傳用戶：szcyclone
Reconstruction- and example-based super-resolution (SR) methods are promising for restoring a high-resolution (HR) image from low-resolution (LR) image(s). Under large magnification, reconstruction-based methods usually fail to hallucinate visual details while example-based methods sometimes introduce unexpected details. Given a generic LR image, to reconstruct a photo-realistic SR image and to suppress artifacts in the reconstructed SR image, we introduce a multi-scale dictionary to a novel SR method that simultaneously integrates local and non-local priors. The local prior suppresses artifacts by using steering kernel regression to predict the target pixel from a small local area. The non-local prior enriches visual details by taking a weighted average of a large neighborhood as an estimate of the target pixel. Essentially, these two priors are complementary to each other. Experimental results demonstrate that the proposed method can produce high quality SR recovery both quantitatively and perceptually.
標簽： Super-resolution Multi-scale Dictionary Single Image for
上傳時間： 2019-03-28
上傳用戶：fullout
The idea of writing this book entitled “Cognitive Networked Sensing and Big Data” started with the plan to write a briefing book on wireless distributed computing and cognitive sensing. During our research on large-scale cognitive radio network (and its experimental testbed), we realized that big data played a central role. As a result, the book project reflects this paradigm shift. In the context, sensing roughly is equivalent to “measurement.”
標簽： Cognitive Networked Sensing Data Big and
上傳時間： 2020-05-26
上傳用戶：shancjb
This book describes how global mobile communication was made. It is written for those who want or need to know how this was achieved e.g.: ? Young professionals who want to build their career on GSM and UMTS and need to understand the basics ? Strategic and technical planners who want to drive the future GSM and UMTS develop- ment ? Strategists who plan to repeat GSM’s success in the fourth generation ? Academics, who want to understand and analyse the development of GSM and UMTS; ? Activists in other large scale international communication projects who want to use experiences gained
標簽： Creation UMTS GSM and The of
上傳時間： 2020-05-27
上傳用戶：shancjb
This books presents the research work of COST 273 Towards Mobile Broadband Multimedia Networks, hence, it reports on the work performed and on the results achieved within the project by its participants. The material presented here corresponds to the results obtained in four years of collaborative work by more than 350 researchers from 137 institutions (universities, operators, manufacturers, regulators, independent laboratories and others – a full list is provided in Appendix B) belonging to 29 countries (mainly European, but also from Asia and North America) in the area of mobileradio. Theobjectiveofpublishingtheseresultsasabookisessentiallytomakethemavailable to an audience wider than the project. In fact, it just follows a ‘tradition’ of previous COST Actions in this area of telecommunications, i.e. COST 207, 231 and 259.
標簽： Multimedia Techniques Broadband Networks Mobile
上傳時間： 2020-05-30
上傳用戶：shancjb
Since the principle of multi-carrier code division multiple access (MC-CDMA) was simultaneously proposed by Khaled Fazel et al. and Nathan Yee et al. at the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) in the year 1993, multi-carrier spread spectrum (MC-SS) has rapidly become one of the most wide spread independent research topics on the field of mobile radio communications. Therefore, the International Workshop on Multi-Carrier Spread Spectrum (MC-SS) was initiated in the year 1997. Multi-carrier and spread spectrum systems with their generic air interface and adaptive technologies are considered as potential candidates to fulfill the requirements of next generation mobile communications systems.
標簽： Multi-Carrier Spectrum Spread 2007
上傳時間： 2020-05-31
上傳用戶：shancjb
The ever-increasing demand for private and sensitive data transmission over wireless net- works has made security a crucial concern in the current and future large-scale, dynamic, and heterogeneous wireless communication systems. To address this challenge, computer scientists and engineers have tried hard to continuously come up with improved crypto- graphic algorithms. But typically we do not need to wait too long to find an efficient way to crack these algorithms. With the rapid progress of computational devices, the current cryptographic methods are already becoming more unreliable. In recent years, wireless re- searchers have sought a new security paradigm termed physical layer security. Unlike the traditional cryptographic approach which ignores the effect of the wireless medium, physi- cal layer security exploits the important characteristics of wireless channel, such as fading, interference, and noise, for improving the communication security against eavesdropping attacks. This new security paradigm is expected to complement and significantly increase the overall communication security of future wireless networks.
標簽： Communications Physical Security Wireless Layer in
上傳時間： 2020-05-31
上傳用戶：shancjb
Quality of Service ( QoS ) has always been in a world of its own, but as the technology has been refi ned and has evolved in recent years, QOS usage has increased to the point where it is now considered a necessary part of network design and operation. As with most technologies, large - scale deployments have led to the technology becoming more mature, and QOS is no exception.
標簽： QOS-Enabled Networks
上傳時間： 2020-05-31
上傳用戶：shancjb
It was only a few years ago that “ubiquitous connectivity” was recognized as the future of wireless communication systems. In the era of ubiquitous connectivity, it was expected that the broadband mobile Internet experience would be pervasive, and seamless connectivity on a global scale would be no surprise at all. The quality of service would be guaranteed no matter when/where/what the users wanted with the connectivity. Connectivity would even be extended to object-to-object communication, where no human intervention was required. All objects would become capable of autonomous communication.
標簽： Protocols Radio LTE-A LTE for and
上傳時間： 2020-06-01
上傳用戶：shancjb
This book was born from the perception that there is much more to spectrum use and sharing than one sees reflected in publications, whether academic, commercial or political. the former – in good research style – tend towards reductionism and concentrate on specific, detailed aspects. commercial publications tend to empha- size the positive aspects and they tend to put promise above practice. Given the ever increasing pace of technology development and recent successes of new wireless technologies, some pundits predict large-scale spectrum scarcity, potentially lead- ing to economic catastrophe. Although economic theory has a hard time explaining recent events that shook the world economy, the notion of spectrum scarcity is intui- tively acceptable, even if not correct or immediately relevant.
上傳時間： 2020-06-01
上傳用戶：shancjb
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