HDMI DDC/CI monitor brightness

Does anyone know, if we can control the monitor brightness via DDC/CI? I’m running the latest build of Windows IoT Core on my Dragonboard 410c, and have working code as a console application, which does work on my PC, but does do nothing, when running on my Dragonboard. Or are there other options, to control the brightness?

Best Regards

From a hardware point of view I think the DDC/CI endpoint sits on the same I2C bus that is used to read the EDID. I’ve never played with DDC/CI controls but the hardware can certainly read EDID OK. Having said that I cannot comment on whether this is enabled for Windows IoT though since, for anything more complex than a simple “does it install” test, I’ve never used anything but the Debian images for this board.

You might be better off asking this on the Windows 10 IoT MSDN Support Forum . You are certainly very welcome to post here but there really aren’t very many Windows users hanging out on this forum. It is possible your question will resonate with somebody but I’m afraid it isn’t very likely you’ll get a useful reply here. In short, you might attract more eyeballs on a different site.

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Thank you for your answer. So then it shouldn’t be a problem with the board itself? In other words, when you use a Debian image, you have the ability to control brightness of a HDMI attached screen out of the box?

Somewhere in the middle.

I’ve not tested it personally… but for a DVI-D display device one expects to see the EDID (i2c addr: 0x50) and DDC/CI (i2c addr: 0x37 IIRC) on the same I2C bus. I do know we can read the EDID making it pretty much certain the hardware can handle DDC/CI.

The alternative is that I have grossly misunderstood the spec and I’ll have to leave it to you to assess the probabilities each way on that :wink: !

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Okay I see. So would it be possible, to directly access this I2C bus somehow for exact this purpose?

I haven’t tested it either, the HW is fully capable, and in theory the SW is in place to access it, so hopefully it will work. If it doesn’t work, you really need to test your monitor. Not all monitors implement DDC/CI, and many of those that do implement it have bugs.

Good Luck, and please report back to us if it does work.

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Thank you @ljking. My monitor is capable of this feature. I have a small console application, which does work on full Windows 10. I compiled it for ARM, but there seems to be some missing methods inside the “User32.dll”, which get called…

I’m afraid I simply don’t know the answer for Windows IoT… what you describe is exactly how most of the ddc/ci tools for Linux work.

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Try this article: https://www.raspberrypi.org/forums/viewtopic.php?t=152495

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Thank you, will give it a try and ask there :slight_smile:

Inside the dragonboard hardware manual, i found this:

GPIO F Connects to MPP_4 of PM8916 PMIC. It is a 1.8V signal. Can be configured to be the DSI backlight control

Would this be a way to have control over the brightness?

Only if you have a DSI display. I thought you had a HDMI display with DDC.

Oh okay i didn’t realize that, yes i have a HDMI display with DDC. Do perhaps some adapters or interfaces exist, where we can send i2c commands to the HDMI?