Simple ambilight clone is just a few transistors

The Ambilight system – built in to high-end Phillips TVs – is a neat system to add a bit of ambiance to regular television viewing. With this system, a series of RGB LEDs are mounted to the rear of the TV to respond to whatever is currently being displayed. [Lovro] came up with a very simple way to add an ambilight system to his computer monitor using only a handful of components.

Unlike other Ambilight clones we’ve seen controlled by custom software or a Processing sketch, [Lovro]’s system uses a few transistors wired to the red, green, and blue pins of his VGA cable. Each of these lines is connected to an RGB LED, so the intensity of each color is determined by the amount of the respective color on the screen.

There is a down side with this setup: a second video output in a mirrored mode is required for this hack to work. Luckily, [Lovro] has a dual-monitor graphics card, making setup a (relative) breeze.

You can check out [Lovro]’s videos of his Ambilight clone in action after the break.

36 thoughts on “Simple ambilight clone is just a few transistors

  1. so the schematic – http://imageshack.us/photo/my-images/546/20939579.jpg/ says that the input impedance of a monitor is low, and the transistors used to drive the LEDs load the signal, so you cannot use the same cable for both the monitor and LED’s. Perhaps I’m missing something, but why not use some FETs to drive the LEDs instead, as they have a high input impedance they shouldn’t load the VGA signal….

    1. The problem is not the impedance itself, but the fact that you are going to get a very small current to drive the transistor.

      You could do a 2 stage amplification, but then it wouldn’t be so simple. :oP

    2. But FETs, especially power MOSFETs have pretty big input capacitance, which will load the RGB signal lines. The signal’s bandwidth can be as much as a few megahertz.
      Proper buffer amplifiers driving power amplifiers would fix the problem.

      1. The FET gate capacitance would not affect the picture much if they would be connected by a high value resistor.

        This would of course act as a low pass filter but that shouldn’t affect the operation since the led’s is only displaying average values of the picture anyways…

      2. It would still distort the picture, and who wants to use VGA on a digital panel when you can use an actual digital connection?

      3. @Dax – Someone who is already using both outputs to drive two monitors non-cloned and doesn’t want to add a second video card or can’t since most motherboards are so tight on expansion ports these days. (I think tablets and desktops are converging… in a bad way)

      4. My video card, as well as many modern cards, has a vga port as well as hdmi. I both outputs simultaneously and as far as I remember, the card did this out-of-box. It’s nice to see such a quick and easy project.

  2. Impressive built very nicely done sir, how about taking an old pci video card and hooking up a couple of led strips?

  3. To avoid needing two outputs he could have spliced a couple of leads into the primary video cable. If he isolated the led circuit from the cable with a voltage following op amp it wouldn’t interfere with the video feed.

    Either way, very cool build. I think I’ll give it a shot soon!

  4. aayotee you got that comment in just before me. I suspect however, that the issue might be more of an attenuation issue due to the frequencies involved, so perhaps some better coupling, (caps and ferrites, rather than just resistors), some screening and the aforementioned FETS would do the trick. Its a neat and simple idea, just needs a little more refining, (and it wont work for digital/hdmi of course, just good old (S)VGA).

  5. One other idea – what about a VGA splitter/amplifier? These are typically used for connecting a projector and a monitor, but could be used for connecting 2 monitors. Actually, in years past, big box electronics stores would use these to display a bunch of monitors. There’s an amplifier for each output, so the outputs don’t affect each other.

    1. Yeah, I agree about splitter, you can find some schematics to build your own also with few transistors, but you can buy it also, I think the are cheap! Thank you for support! :)

    1. 1+ You beat me to it that’s what I clicked on the comments to say!
      Good use for and Old, slightly messed up, small, or otherwise unused display, just turn the brightness all the way up.

  6. Nice build, I wonder if the HSync signal line could have been used to adjust the individual LEDs to represent the various portions of the screen.

  7. Sure I saw something in Elektor a while ago that did proper Ambilight-style, including different colours for the top / middle / bottom / left / right areas. And he did it all in analogue, just for the hell of it.

  8. BTW… what about mosfets? Maybe they will not suck enough power from RGB signal to screw video output so you can use it even with monitor on the same VGA port…

  9. I wonder for people that don’t have VGA ports on their display card, could we use one of those USB to VGA adaptors. I’m assuming USB should have enough power to drive the RGB leds.

  10. I think that ve should also note that this will probably work with other kinds of RGB signal like classic RGB (3 cables with cinches), S-Video or some configurations of SCART. And if you don’t mind having just single color (white), you can also try composite video signals…

    1. S-video obviously won’t do it, but SCART has RGB output though as you say, that is used now most often instead of the composite signal lines.

  11. ok. I am going to be the dumb one to ask the dumb question…

    What is the point of ambilight? Is it to remove the harshness of quickly changing brightness in video? I never really understood the point of this.

      1. Thanks, JB, sounds pretty much like I guessed. I’ll pass. lol. Seems more like “underglow” for your TV.

    1. I’m not a huge fan of it for movies but for games or music videos it’s another thing altogether.
      I mean for a home-made setup, it doesn’t warrant paying a lot extra for really.

    2. Mind you they also had a system for computers that included game-activated fans for wind effects and various rumble attachments.
      Although not many games supported that in the long run.

  12. Does this require a actual, live monitor being connected to the VGA output (my TV is connected via HDMI)?

    Would like to fool my HTPC into thinking that the “ambilight” is another monitor that it has to mirror the main one to. But I can’t seem to get it to detect the electronics on the VGA as a legitimate screen, despite terminating the RGB and sync leads with 75/600 Ohm resistors.

    Would prefer the simplicity of an analog solution like this but can’t get even get a signal!

  13. What about the DVI port?

    It has pins for both a digital and an analog signal. Could you use both signals at the same time so you would only need one output? Then route the digital to your screen and the analog to your leds.

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