Sunday, June 01, 2008

DVRs, TVs and infrared sensors

If you'd prefer to read this post in Portuguese, check this post at my other blog.

I've recently joined the new Tivo-like service in Portugal, which is called Meo (in Portuguese). The installation was done without any problems and the service was working perfectly. During that day, I tested all features and I was quite amazed on the potential of the service.

When my wife arrived home (she arrived around 8 P.M.. Yes, this will be relevant.) I wanted to show her the newly acquired gadget. Suddenly, the DVR box wasn't responding. The remote was sending the infrared signal (see NOTE for an interesting diagnosis tool) but the box wasn't receiving it. I had to be standing at about 1 meter (around 3 feet) for the DVR box to receive the signal from the remote and execute the desired action.

So, I called the help desk and told them about the problem that I was having. They told me that the remote had a problem and that I should replace it in a store. And so I did. The next day, I went to a store with the remote and explained the problem again to one of the technicians. After doing some testing with my remote on their DVR box, the technician tells me that there isn't anything wrong with my remote.

So, I decided to go back home (around lunch time) and test the all thing again and to my surprise, everything was working perfectly. I thought: "Ok, last night the remote had a glitch but it's gone now". But at night the problem came back again. So, after a new round of calls to the help desk service and discussions with store technicians, they decided to send a team to my house to check out the problem. Of course, I told them that the team would have to go there at night, since the problem was only manifesting at that time.

And so they did. The next night, a technician went to my house and at first, everything was working (he arrived around 7:30 P.M.). At this point, my anger was starting to rise to dangerous levels. But as soon as the technician was starting to say (around 8 P.M.): "Ok, it seems that there's nothing wrong with this, so there's nothing I can do", the problem started to manifest again.

The technician decided to change the DVR box with a new one, but the problem remained. He was even more amazed than I was because he wasn't able to understand why this problem was occurring. We started thinking about interferences with other devices on my living room. I removed everything that could cause any interference at the infrared level (DVD Player, Playstation, laptop...) but still the problem remained. It was only when the technician placed the DVR box away from the television (about 3 meters away) that we started seeing some improvement (but it didn't solve the problem entirely).

The technician (very intelligently!!) concluded that the interference was caused by the television and that there is nothing he could do, that the only way to solve this was to place the DVR Box really far away from the television. Oh really? Thanks genius!!

But of course, I wasn't satisfied with this diagnosis, especially because the problem was only manifesting at night. So, after searching (for about 2 hours) the web for similar problems, I finally discovered what the problem was. But first let me tell you about what I've learned and what I've tried:
  • Infrared light is present in sunlight and fluorescent light bulbs (the ones usually found in kitchens) and so these sources of light should not exist in the same place as infrared devices - it wasn't my case
  • Having white walls directly facing the DVR is also not a good idea, because the light reflected on the wall (from various light sources, including the TV images) may also interfere with infrared devices - I have in fact a white wall on the back of my couch which is facing forward the TV and the DVR but that was not the cause of my problem
  • Other people have complained about the interference that some wireless routers cause in infrared devices - this wasn't my case and I find this very hard to believe as one is based on infrared light and and the other is based on radio signals
  • Some people have also complained that the excess of light in a room can cause interferences with infrared devices and that a bit of duck-tape over the infrared sensor of the TV or DVR should help filter the light sources - this wasn't my case
It was only after thinking a lit bit more about the fact that the problem only occurs at night that I decided to analyse the problem from another angle: check the settings of the TV to see if anything was changing at that time of the day. I didn't find anything that would explicitly change the TV settings at a certain time of the day but I did come across a very interesting functionality: dynamic light adaptation.

My Samsung LCD has this functionality to adapt the screen brightness and contrast according to the amount of light that exists in the living room. For example, if it's bright enough, the TV adapts to display a more bright and contrast image and vice-versa. So, I decided to turn off this option and guess what... everything went back to normal again.

I don't know the details on how this functionality affects the communication between the DVR box and the remote (maybe the TV's infrared sensor for this feature uses the same light frequency as the DVR box and remote), but now it's easy to understand why this was only occurring during that time of day (around 8 P.M.): because this was when the light in my living room (which is faced West) was changing because of the sun going down.

I've been using the system for a few weeks now (with the TV and the DVR standing really close) and since then, the problem has never occurred again :-) So, if you're having a similar problem with infrared interferences and you're unable to detect the source of the problem, remember to check your TV settings for any dynamic light adaptation.

NOTE: this tip works for all infrared-based remotes. To diagnose a problem with your remote, simply point it to a camera-based cellphone (or any other camera, such as a webcam or camcorder) and click any button. If you see a light blinking, then it's working properly. Because remotes work with infrared, this blinking light will only be visible in the camera and not at the naked eye.


Luís Silva said...

Thank you for sharing this! ;o)

I would probably never think about checking something like the TV settings!


Anonymous said...


This is completely true. Many LCDs now have a feature that adjusts the LCD backlighting automatically by using an infrared sensor (that sends out a infrared signal) to the surrounding area around the TV. If you are using a remote control that uses Infrared also, this can interfere with the remote ranging from changing channels on the receiver to blocking out the functionality of the remote. The reason this was occurring at night is the IR sensor was busy and probably sending an interfering signal.
Pass on to friends.