2.8 TFT - Can't get it working

Other Hardware Displays
1

Greetings, everyone!

Recently, I purchased this screen from AliExpress, along with an adapter plate to experiment with.

In my initial testing, I can get the screen connected, and partially working. I've had success in getting readings from the touch panel. I've had success in reading which driver it is - It claims it is the HX8347G. However, I can't get the screen to work. All I get is backlight.

And, speaking of backlight, this screen has six instead of the normal compliment of four - Pins 11 and 21 are the additional LED-K pins. I've connected pins according to a similar LCD screen shield I picked up a while back, using the standard ST7781R pinout, which seems to be at least somewhat right (As said, touchscreen works, backlight works, can read the chip info).

Any idea on what's being done wrong? I'm using one of the libraries from this thread, as it's what allowed me to get the shield working, but so far have had no luck. As said, it detects the HX8347G chip, but I get no display on the screen.

2

First off, you need to ensure that ALL your logic signals are 3.3V.

Yes, these modules do tend to follow similar pinouts.
I can't read the numbers from the photo in your link. But you can. Post the model number here.

Read the controller ID. A HX8347-G returns 0x7575 by reading reg(0).

David.

3

Think the issue may be the 3.3v - I was trying to run off of an Uno, and even supplying the 3.3v, the logic pins will be 5v.

The controller ID was returning 0x7575 - It was your modification to the Adafruit libraries that I'm running, and it returned that it found the HX8347G after checking the ID.

Question: I'm intending to run these screens from boards that are using 2 AAA batteries for power. Will they run fine off of 3v (And less), or will I need to put a regulator on there to get them to work?

And, finally: I'm not sure which numbers will be relevant, so here's pictures of every number on the screen (Images are links):


4

Yes, they will run fine on 2.8V. (or 3V)

They will be killed by 5V from a Uno. You must use 3.3V (or lower) logic levels.

The HX8347-A, -D, -G, -I are not in the current release of my Library. Which uses Adafruit_GFX but is otherwise not "modified Adafruit TFT" library.

I do have unreleased support for HX8347-D, -G, -I. If someone has an HX8347-A, I could get that working too.

If you have a choice, I would not choose Himax.

David.

5

Hmm, I think it might have been someone else's library then.

What issues do you have with Himax? Realistically, I chose these screens because they were the cheapest I found. If there's a good reason not to use them (Which it seems you have), then it's worth the extra money not to use them.

6

They have Read issues in SPI mode.

Accessing Registers is a lot slower than with say an ILI9341.

My main "irritation" with Himax is that the same model number has different Registers with each suffix.
Actually, HX8347-D, -G, -I are similar. But -B, -A are completely different.

There are anomalies with the HX8357 model. -B, -C are different.

Quite honestly, the bare modules are pretty cheap from any manufacturer. I would go for MIPI compatibility.

Otherwise, Himax displays are probably as good as any other make.

David.

7

I'm not using them in SPI mode (As far as I know. I'm using more than a few pins...). As far as speed, it's not exactly one of my priorities. I'm using these for a digital convention badge, so once it loads up the image (Be it programmed in or loaded from a bitmap), it'll generally stay there for a while.

The model numbers do seem to be a large irritation, and it makes sense now that you'd want it clarified in the register.

Thanks for the information. I'll get back on if I can get it going with 3.3v or not.