Consider a run off the mill pc: lcd displays connected, you have brightness control in the menu of the lcd. And some other stuff like color temp and modes.

Now consider a laptop, AIOs and kiosk PCs. Light sensors turns brightness up and down, proximity sensors switches the actual display on or off. And the OS have access to these readings and gives control over it (like a brightness slider for example).

What interface does this controller use to talk to the computer? I've been googling around and there are mentions of GPIOs, or I2C via SMBus, but it might have been deprecated in recent years. What is the current top interface for this usage?

Anyone with experience on this? Does this involves custom motherboards with gpio or extra smbus? I know some embedded Mobos have gpio and i2c header, and on laptop scene I guess the manufacturer can have anything they want. Are these interfaces simply not available on consumer Mobos?


1 Answer 1


Not sure what this question is about. Yes, brightness is controlled by changing intensity of backlit LED, which requires a separate controller (usually interfaced with mainboard via a serial link, I2C or SMBus). Yes, proximity sensors are also INDIVIDUAL devices that must be interfaced with mainboard, again via I2C or SMBus. So the mainboard, if you want it to control brightness and turn it completely off via proximity sensor, must have a dedicated CONTROLLER in PC I/O space, and a corresponding driver to let application software to access this controller. Typical consumer "mobos" usually don't have this, although many chipsets do have a channel to do this kind of job, usually via a dedicated peripheral "super I/O chip" connected via the standard 4-bit-wide LPC bus. Consumer mainboards usually don't expose this functionality to user space.

Many stand-alone (VESA-compliant) displays have a side-band communication channel called DDC, which, if configured/used, and your video card supports it, can control brightness and all other settings in the display.

If your intent is to use a cheap consumer mainboard in a kiosk-like application, you need to consider the special class of "embedded mainboards", PC-cards, etc, which are, unfortunately, quite more expensive.

  • \$\begingroup\$ It is exactly what I'm asking. Thanks! I'm diy ing a screen out of a broken laptop and wonder if I can make a board and write a driver so windows can control it. Looks like I can't. \$\endgroup\$
    – Evan
    Oct 7, 2018 at 19:29

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