Identifying a 3.3" TFT Touch MEGA 2560 display board & using it with MCUfriend

Other Hardware Displays
1

I have this 3.3" TFT Touch MEGA 2560 display from an eBay vendor who seems to know almost nothing about the board. The only thing they could do was send me the standard UTFT library. So I need some help recognizing this board and hopefully tracking down more info about it...

I think the display controller is a 9481 or similar but I'm not sure yet. The display itself works fine if I tell MCUfriend it's a 9481 and it fails in the same ways as a known 9481 if I tell MCUfriend it's a 9486 instead.

I have three specific issues: Backlight, Pinout and Touch

  1. By default the Backlight is extremely dim, as if it's at a minimum setting or possibly off all together. Is there a software (or hardware) way to activate the Backlight?

  2. Anyone have the pinout or schematic for this board. It has way more pins than the typical MEGA compatible display and of course some of them are for the touch panel. But what are the others for and specifically can I have it NOT use the A8-A15 analog pins since I use those for other purposes.

  3. When I get to the point of wanting the touchscreen, how do I use it?

Since it has a MEGA interface I believe it doesn't have a way to read out the controller type nor any of the board's or contgroller's register values. Anyone recognize this board? Ideas?

IMG_1271 (1).jpg
IMG_1271 (1).jpg1280×960 435 KB

IMG_1275 (1).jpg
IMG_1275 (1).jpg1280×960 498 KB

IMG_1274 (1).jpg
IMG_1274 (1).jpg1280×960 383 KB

2

I suspect that the screen is write-only.
Please quote the i.c. part numbers.

Look in the extras/mcufriend_how_to.txt
Try every 320x480 controller ID.

Which gives the best picture.
Don't worry about directions. Worry about good colours and steady picture.
Make notes on paper

Report back.

David.

3

Hi David

The three visible ICs are all LC245A, which apparently are bidirectional bus transceivers. So I suppose there's some chance some info could be read from the display board.

Now I'm curious what particular deficiency makes many MEGA 2560 display board Write Only? And are any of them also Read capable?

Thanks, Joe

4

Googling LC245A always seems to come up with Texas SN74LVC245A

Generic HC245 is not input voltage tolerant. The LVC245 is tolerant of 5V input voltages.

Regarding Mega2560 Shields and Adapters. I have no idea why Itead, ColdTears, ElecHouse, ... chose to ignore the LCD_RD pin. Almost every Mega shield either has bidirectional buffers like LVC245 or series resistors.

If they had wired them correctly you would have Write-Read capability.

Likewise, the de-facto standard for shields puts the SPI Touch controller on GPIO pins instead of on the SPI bus.
UTFT supports these displays. URTouch can bit-bang the Touch Controller.

I would be 99.95% confident that the Chinese pcb designers know exactly what they are doing.
Of course the Lingerie shops on Ebay probably know nothing about electronics.

You can follow the pcb traces to pin#1 on your LVC245 chips. If hard-wired to 3.3V the buffers are uni-directional i.e. screen is write-only.

Have you determined which 320x480 controller is on your display?

There are subtle differences in behaviour of the MADCTL register.

David.

5

So far the display itself seems to behave best with the 9481 driver setting, but I haven't tried them all yet.

I got the touch screen figured out yesterday. Biggest issue was that three of the four ribbon cable conductors had bad solder joints so it took me a while to figure out which Arduino pins carried the Touch signals. Once I fixed the bad solder joints the touch shows up as a standard 4 wire resistive panel on A0-A3.

#define YP A3
#define XM A2
#define YM A1
#define XP A0

So now the tftpaint demo works.

And I'm happy to say that although the display shield has connector pins for A8-A15 it doesn't seem to interfere with my use of those pins for other purposes.

The last and most significant issue is that the backlight is very very dim. I wonder if some of those extra thru-holes are intended to control the backlight level? They're marked A10-A15, 12, 14, 17, 19, 43, 46, 48, which sounds like Arduino pins numbers to me...

Or if there might be a register in the 9481 used for that. There a bunch of commands to control various power levels but I have no idea if any of them affect the backlight.

So another mystery to solve....

6

Most Chinese pcbs are well made with good soldered joints. (except Sainsmart)

You should be able to use regular Touchscreen.h library for your resistive Touch panel.

It looks as if the extra holes are for your convenience. When the shield is in place you can access the empty header sockets with angle header strip. Or the "unused" pins from the DIGITAL, ANALOG, POWER headers via the extra holes.

I would expect the TFT to work with UTFT model: ILI9481
MCUFRIEND_kbv needs USE_SPECIAL, USE_MEGA_16BIT_SHIELD, tft.begin(0x9481)

i.e. data bus on 22-37. control pins on 38-41, SD on 50-53

You can investigate the pcb traces with eyes and a DMM.
Write the results on paper. Report here.
What value is R1? Where does it go?

David.

7

Hi David

I think you might have put your finger right on the backlight issue. I had never even paid attention to R1 before, but it measures almost exactly 100 Ohms on the dim board and a similar resistor always named R1 always measures 2.2 Ohms on other boards of three different designs. I only have one example of the dim board, but I ordered two more today and I'll compare how they look by default and what their R1 values are. I suspect I could solve the Backlight issue by using some other resistance value closer to 2.2 Ohms than 100.

Thanks for pointing me in what I think will be the right direction. Signs are looking very positive so far.

I also need to check if either side of R1 shows up on a connector anywhere. Might be designed to support an external brightness control, that would be a very nice discovery.

8

In case anyone is still following this or needs this info in the future, the Backlight issue was related to R1 just like David predicted.

The display arrived with R1 as 100 Ohms and the display backlight was visible but very very dim. It's hard to imagine it being useful that way except possibly in a night vision application.

Virtually every other board design I have uses a 2.2 Ohm resistor for that function. So I tried various alternative values eg 75, 50, 10, 7.5, 4.9 and 2.2 and finally at 2.2 this board has just about the same brightness as all the other boards.

So after just a few tweaks this turns out to be a very nice high speed Mega 2560 display board with a touch screen and it now looks great. Pretty cheap on eBay for about $16... so I've ordered several more...