Infrared light and signals

Since a long time the consumer electronics industy has been employing infrared remote controls for the control of television, VCR's and many other products. This same technic is popular In industrial- and officeapplications like control your pc to eliminate expensive keypads and cables. It's easier to use the infrared light than cables who always crossing each other. We humans can't see infrared light because the wavelenght of infrared light is below the visible spectrum(Some animals can see it and use it as a target for killing the prey). Because we don't see ir light we use it for remote control purposes. In remote controls the light source is a led but around us there are many objects who are emitting infrared light. The brighest source is the sun. In fact everything that radiates heat is also emitting ir light like flames, light bulbs, and even our body.

Decoding infrared signals The only hardware you need for decoding IR signals is an infrared receiver. There are two main principles of ir remote controle: using a modulated beam at a frequency about 40kHz or the second is an non-modulated beam of IR light and has a restricted range. The three layers of an infrared signal Three typical layers are used by remote contrals. The names used for these layers has not been standardized. But we can call it the infrared, the modulation and the serial data. The infrared layers is the means of transmission. We can't see infrared light because the wavelenght is too long to see. Altough you cannot see the infrared beam, it behaves the same as light, so if you can't see the target device, you can't control it with a ir remote control. To control applications through opaque materials, radiofrequency signals are used. The modulation layer refers to the fact that each burst of infrared signal is often modulated at a frequency between 32.75 kHz and 56.8 kHz. This is done to diminish the effects of ambient light. This layer, however, is optional. Some infrared formats do not modulate their outputs, sending pulses of unmodulated infrared light instead. This is done to extend the remote control’s battery life and to reduce the cost of the remote control device. The serial data layer has the information containing a command. This is typically coded in the lengths of infrared bursts or in the lengths of gaps between infrared bursts. Ex. A long gap or burst is interpreted as a '1', a short gap or burst is interpreted as a '0'. Transmitting and receiving IR lights Transmitting IR light is fairly simple done by using an infrared led. Like normal leds emmiting light waves in the visible ranges, ir leds are doing this with a light invisible for human eyes. But when you will see the ir beam, take a webcam and point the remote control to the cam and you will see a flashing light. Receiving and decoding the signal is a lot harder. The ir light is captured by an ir sensitive photodiode with the highest spectral sensivity around 950nm. The output signal is optical filtered, amplified and passed through a signal filter tuned to the frequency of the emitted signal frequency. The best and most easy to use are the integrated 3 leg ir receivers like the Vishay TSOP1836 and the Siemens SFH505A. The output of these devices is TTL compatible, the optical filter, amplifier with automatic gain control, tuned filter, and demodulator are integrated. PC infrared remote control A study of different remote control protocols can be found on the other pages of my site.You can also find the source code for a pic16f628 to decode the sony infrared protocol. With this you can control you pc with an infrared remote control. It's now only available for the sony code, but I will add in the future other protocols also. With a program running on the pc it will be easy to control windows,winamp or other applications.