全面了解红外遥控参照.pdfVIP

全面了解红外遥控 IR Remote Control Theory The cheapest way to remotely control a device within a visible range is via Infra-Red light. Almost all audio and video equipment can be controlled this way nowadays. Due to this wide spread use the required components are quite cheap. Thus making it ideal for us hobbyists to use for our own projects. This part of my knowledge base will explain the theory of operation of IR remote control, and some of the protocols that are in use in consumer electronics. Infra-Red Light Infra-Red actually is normal light with a particular colour. Us humans cant see this colour because its wave length of 950nm is below the visible spectrum. Thats one of the reasons why IR is chosen for remote control purposes, we want to use it but were not interested in seeing it. Another reason is because IR LEDs are quite easy to make, and therefor can be very cheap. Although we humans cant see the Infra-Red light emitted from a remote control doesnt mean we cant make it visible. A video camera or digital camera can see the Infra-Red light as you can see in this picture. Unfortunately for us there are many more sources of Infra-Red light. The sun is the brightest source of all, but there are many others, like: light bulbs, candles, central heating system, and even our body radiates Infra-Red light. In fact everything that radiates heat, also radiates Infra-Red light. Therefor we have to take some precautions to guarantee that our IR message gets across to the receiver without errors. Modulation Modulation is the answer to make our signal stand out above the noise. With modulation we make the IR light source blink in a particular frequency. The IR receiver will be tuned to that frequency, so it can ignore everything else. You can think of this blinking as attracting the receivers attention. We humans also notice the blinking of yellow lights at construction sites instantly, even in brought daylight. In the picture above you can see a mod