Auto dimming LCD backlight with ambient light sensor project

htevents said:

The end result should be the following:
Android mini pc with HDMI out to LCD display (HDMI in). No fancy things there except for the fact the LCD has to dim when the ambient light gets darker.
The display to be used is 7 inch. I have not chosen a display yet, because I don't know wich one to take, due to the fact I need a certain LCD driver that can handle an ambient light sensor (ALS) to auto dim the backlight.

Any thoughts about this?

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Nigel Goodwin said:

Is it for use as a display in a car? - because for normal TV or pretty well any other sort of display use the first thing you want to do is disable such silly features, as it completely ruins your viewing.

It's a 'feature' which has appeared now and again on TV sets going back to at least the 50's, and has become commonplace in the past few years - and it's utterly crap!, and always has been. We used to modify the few old B&W valve sets that did it, to remove the 'feature' as the customer couldn't disable it back then.

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gophert said:

I would use a Raspberry Pi 4 and the Raspberry Pi display. You can directly program the backlight brightness of the display from the pi. One value in a file on the pi.
You'll need an ADC to convert an analog ambient light value to something the Pi can read (no on-board ADC).
A light-dependent resistor and a 10k fixed resistor in series is as simple as it gets for ambient light. Or, a green LED reversed biased with a 33k to 100k resistor works too. Connect the node between the two resistors to the ADC input and read result with Pi. Then decide what brightness you want to translate to with code.
Cheers.

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htevents said:

Thank you very much for this in depth reply. I already had a quick look to a similar solution, the only problem I then run into is: how do I get the video signal of the Android device on the display?

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Nigel Goodwin said:

I thought you were using HDMI?.

But if your display has an available connection to the backlight?, you could even do auto-brightness with a bit of hardware, using an LDR to vary the backlight current. Everything really depends on your exact display, and what facilities it offers.

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htevents said:

Yes, I do use HDMI, so what you are saying is that I have run the video signal from the Androidbdevice thru the RPi? I thought the RPi couldn't handle video input, only output (at least not HD signals).

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Nigel Goodwin said:

I think he was suggesting using a PI instead of using Android?.

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gophert said:

Just screen cast to RPi from android

How to Make Your Own DIY Chromecast With a Raspberry Pi

Want to save a bit of cash on a Chromecast? Here's how to make a DIY Chromecast with a Raspberry Pi and a mobile app.

www.makeuseof.com

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htevents said:

Hmm that is interesting. The thing I have to overcome is that the Android device will likely be an Android mini pc. This has no display by itself, so I can't start a cast without controlling the mini pc. Maybe Macrodroid or Tasker can be helpfull for that purpose.

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