LCD/TFT for embedded applications - General questions

LCD/TFT General Q's

Hi all,

I'm wondering what you guys think of large LCD/TFT screens in embedded applications. I'm defining large as 5-13" diagonal. I don't really have a specific application in mind, but I'm just curious if people prototype with screens this large. It seems even finding a small, 3.5" LCD is pretty tough (eBay, SparkFun) and expensive. It's amazing to find a 3.5" LCD for $70+ when you can get a 22" one for $140. Are small LCD screens really expensive in production applications?

I guess the application I have in mind is reconfigurable lab equipment that has nice user interfaces. I'm talking about touch screen and/or color screens. It seems like these could be added to small quantity, custom instrumentation equipment, for very little, verse a 128x64 monochrome LCD.

Speaking of smaller color TFT displays, in the 3.2 or 3.5" variety, what are common controllers? If I have to write a driver, I only want to do it once.

For character LCDs, there's the HD44780.
For graphical LCDs, there's the KS0108, et el.

What about TFT displays? If I wanted to make QTY 10 or 20 of a particular device, where could I buy these economically?

Thanks for passing down the experience,
Matt

Re: LCD/TFT General Q's

Hi Matt.
Lately I've been working a lot with TFT's in my embedded projects. And even with simple 8-bit AVR - though most of my applications used the 32-bit STM32 ARM!

In general speaking TFT's they doesn't have any SRAM or digital controller. This means that you have to feed the display with RGB data continuously.

Most of the time the small size TFT screens (up to 3.5") have SRAM and digital controllers though. This is because it makes everything a lot easier, and isn't that expensive! But when you go higher that 3.5", you have to go higher in resolution (else the pixels will be to big), and then you need a bigger and more expensive controller. That's why the bigger screens doesn't have any SRAM and digital controller!

Digital controllers are controlled with a simple 8080 parallel interface or a standard SPI interface. In parallel mode you can chose to use 8-bit or 16-bit, and then you have a clock, chip select, RS, RD and WR line. With these you write the RGB data to the digital controllers SRAM, and then the digital controller takes care of feeding the RGB data (from the SRAM) to the display!
You can also use SPI for controlling, but this is very slow as you can guess. Instead of being able to send 1 or 2 bytes pr. clock cycle, then you have to use 8 or more clock cycles for a single byte!

For the small size TFT's, also known as QTFT's, the most common controller is Iltek's ILI9320, ILI9325 or SSD2119. Theese controllers have enough SRAM for a display resolution of 320x240 pixels!

I was getting tired of the small 3.5" display so I started investigating the possibilities. I ended buying a SSD1963 evaluation board and a standard 7" TFT screen with a resolution of 800x480 pixels. This controller was controlled in the same way, I just had to use some other commands, so porting was easy.

OEM 3.5" displays (with controller of course) can be bought cheap on eBay, and even prototype 3.5" displays (also with controller) can be bought for about $50 on eBay. Take this as an example: **broken link removed**

You can see all of my projects here: **broken link removed**
I hope this gave you a better understanding of TFT's and digital controllers!


Best Regards
Thomas Jespersen

Hi dksoba,
Check this links:
7" WVGA 262k color TFT-LCD module with Touch Panel integrated
LVC75Z779 Eval Board Rev.1E

And this:
**broken link removed**
This TFT is 100% compatible use J2 connector.

Have a nice...

That's exactly the board I have. The display isn't from TechToys, but it has the same connection!

Thomas