TFT Display with STM32 LTDC

[Guillaume]

Hello,

I'm not professional designer but hobbyist.
I want to design a new board with TFT display no need for touch.

My goal is to make a first prototype and if it suite what i want i will need about 10 of this.
So i want to break the price. I don't need a lot of color, maybe only black picto can be suitable but think that an RGB666 will better compromise and price not a lot bigger.

Anyway, my first difficulty is to source the display. I think that parrallele RGB display will be cheaper that one with integrate controller and will be more thin.
My constraint are about 16:10 ratio (could be change if easier to find), 3.2" or 3.5".
Be thin (no special value to specify). From what i see display module with controller are a bit big and not flush so having stm32 with LTDC on other board should be a good solution to me.

When i made my search, i have a lot of difficulties to find this kind of RGB display with control signal like VSYNC HSYNC, etc to be use with LTDC. I see a lot of RGB but without this control signal.
The few one that i found was expensive.
My need is only for personal project so i don't car to buy this display to a non professional electronic distributor (farnel, digikey, mouser, etc)

Maybe my idea is wrong but i thought to find this kind of 3.2" display without controller with a price of 10/20€ (or $)

Do you have some advice ? Is my idea to use stm32 with this kind of parrallele display is good ?
And where can i found some reference ? Is the chineese RGB display without signal control can be use with LTDC ?

Thank you for your help !

[pcprogrammer]

Aliexpress is a source to find cheap displays, but finding one for the given dimensions without a controller chip is probably a bit more difficult. Also finding documentation about them is a problem.

Lately the prices have gone up and strangely enough the bigger panels are cheaper then the smaller ones. I bought for instance this panel for euro 9,70, but now it is almost double that. Unfortunately I was unable to find the specifications for it and it is still lying on a shelf until I can use it.

This one on the other hand I bought for euro 13,39 and is now euro 18,56, I did find information about and was able to use with an Alwinner MCU, in RGB565 mode, but the panel supports up to RGB888.

But panels like these do need some additional hardware to make them work. There are several voltages that need to be made for driving the electrodes and the backlight. The interfacing with the MCU it self is straight forward with the signals provided by the controller.

Another issue to consider is memory. To drive a panel like this you need memory accessible by your MCU. This of course depends on the resolution of the display, but even at 128*64 it takes a chunk out of the available RAM in an MCU.

It depends on what you want to do with your system which is better. A 3.2" or 3.5" display with a built in controller takes a way a lot of the hassle and only requires a SPI peripheral in your MCU and some software driver for it, but it will be slower then a display driven from a LTDC peripheral.

[mino-fm]

If 64 colours are enough for you I would like to recommend a 4,3" TFT directly driven by STM32 or any other controller offering the desired on-chip RAM and DMA-controller.
For suggestion please take a look here: http://mino-elektronik.de/TFT-direct-drive/TFT-direct-drive.htm

A very cheap solution uses a RP2040 Pico-Board I'm currently testing. 40 pin standard connector allows to use bigger TFTs (7") or high-brightness IPS type - whatever you need.

P.S.: I add a new picture.

[Guillaume]

Thank you for your feedback.

Effectively, my first search was made on Aliexpress, and as in your link, i didn't find what i want.
Most of the part have no specification and the few that have, don't have the Hsync and Vsync signal.

I read the application note of ST according the LTDC and yes, i think my mcu and internal RAM will be enough to what i want. And for first test i can work with low colors display.

@mino-fm do you have the reference of your  display ? It to bigger for my project, but maybe i can find close ref in ~3.2"

[mino-fm]

I'm using different displays 4,3" and 5,7" from EDT - readable without glasses ;-)
A link where you can find data and prices for TFTs from CN: https://www.buydisplay.com/
But I don't know anything about tax and shipping costs.

[Guillaume]

Thank you mino, I think I have find what I was looking for!
Maybe the only thing that could be bad is the plastic edge that seems to big, but I will test.

My constraints seems respect :
- size
- RGB with control signal like vsync, hsync, etc
- thin, not sure for this point
- cheap : under 10€ for one unit

- oh, no, just see the power consumption, it's too big for my need.. I will take a try with this but have to find a new reference for my final development. Or maybe the TFT technology is not suitable. I need something under 20mA

So I have a new board to design !
I think to use the open source LVGL library on stm32 with LTDC

[gjvdheiden]

Just curious, have you also considered using a parallel 16 bit 8080 interface with STM 32 FSMC? The display would need a driver then.