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Understanding IR Remote Controls

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When hearing the word 'Remote Control', the first thing that comes to most people’s mind would be the TV remote control. They have become so common that other devices - CD/DVD players, Fans, Air-conditioners, Refrigerators, Washing machines etc. - are also getting the same sort of remote controls. These days it's easy to find that almost all consumer electronic devices have a remote control.
Almost all of these are IR remote controls.

What is IR?
IR, or Infrared, is an electromagnetic radiation that has a wavelength between 0.7 and 300 micrometers (frequency range between 1 THz and 430 THz).
The Electromagnetic Spectrum

There are several advantages in choosing IR for remote controls, such as:
  • Low power requirements
  • Low circuitry costs
  • Simple circuitry
  • Portability
  • Few international regulatory constraints
  • High noise immunity 
However, there are a few disadvantages like requiring line of sight, blocked by common materials, short range and light and weather sensitive. Most of these aren't much of a problem with basic remote controls. Interference from sunlight and other IR sources could pose a problem to them. This problem is normally avoided by adding an IR filter that is only sensitive to the specific frequency range of IR remotes (the dark coloured piece of plastic on the remote and on the receiver is this filter).

Another technique is to modulate the IR signal to a frequency between 30 KHz and 60 KHz. Since IR radiation from the sun or other IR sources isn’t modulated, it's easy to filter out the noise caused by them and get only the modulated signal.

Let’s talk about some of the common IR encoding methods used in remote controls in the next post.

References
http://en.wikipedia.org/wiki/Infrared
http://en.wikipedia.org/wiki/Electromagnetic_spectrum
http://trace.wisc.edu/docs/ir_intro/ir_intro.htm
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    Comments

    1. Sandeep EllawalaJanuary 10, 2011 at 9:57 AM

      I was just wondering, now if we modulate Infrared signals into 30KHz-60KHz frequency range, they fall down the spectrum of frequencies and basically propagate as radio signals of low frequency. What kind of changes can we expect in this case compared to IR. For an example, propagation distance would have a direct impact I suppose.

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    2. Thimira AmaratungaJanuary 10, 2011 at 11:06 AM

      My knowledge of theories associated with signal propagation is very low (for now...), but I think the higher frequency determines the propagating distance. So, i think that the higher frequency modulated to a lower is equivalent to the same lower frequency modulated to the higher, which would make the propagation distance the same in both cases. I might be wrong about it. We'll need an opinion of an actual expert in signal physics...

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    3. Sandeep EllawalaJanuary 10, 2011 at 12:47 PM

      Modulating a signal from one frequency to another would not destroy the signal pattern itself. This is what happens exactly in the standard Analog telephone system. Near exact reproduction of a signal of high frequency can be achieved with a lower frequency signal. I have to agree on that with you. But 30KHz - 60KHz is less prone to effects from sunlight and such I think because they belong to ground wave range. Let's see if someone with better expertise can come up with an answer.

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