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CSTroN - CSTN LCD monitor

What if TFT LCD is never invented? Here is the CSTN LCD monitor.

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CSTN was once popular among low-end laptops and cellphones, and its predecessor, STN was almost the only viable option for laptop before TFT LCD was invented. Thanks to the advance of technology, they are fully replaced with TFT LCD. But just for fun, how would software and games today look like on a 90s CSTN LCD?

Basically, this project aims to build an LCD monitor based around a CSTN screen (specifically SX21V004, but once done, it is easy to adapt other panels).

This task would be easy for normal TFT LCDs, one would just need to buy the screen, the driver board, and optionally a case, assemble them together, done. Though one may build driver board and/or case yourself, but given they are easy to find and very affordable, there is not many reasons to build by oneself.

But the story is quite different for CSTN. Most of the large (>3") CSTNs use a very different interface than TFT LCD, making it impossible to connect them to normal driver board designed for TFT LCDs. CSTN driver boards are just no longer available. (But I do confirm that they once existed) Currently, the only solution is to use an FPGA to build a driver board.

This project, once again, utilize my Xilinx ML505 Virtex-5 development board. The on-board VGA decoder is used for capturing incoming VGA video signal, and the CSTN screen is connected to the XGI expansion port. (By the way, Xilinx ditched both ports on their 6 series development boards, making ML505 the last development board with lots of on-board peripherals and a 2.54mm expansion port.)

Currently, the project is basically done. It could capture the VGA signal and display the image on the screen at 60Hz Vsync. STN LCD runs at 120Hz or 240Hz to improve color depth.

  • CSTroN – Monitor powered by an ancient CSTN screen

    Wenting Zhang03/17/2019 at 19:27 0 comments

    Introduction

    Back in the last century, when the CRT was still the most common technology for computer monitors. It was quite common to see such an argument: the LCD will probably evolve and produce better images, but it is never going to replace the CRTs. CRTs are just objectively way superior in terms of image quality, and LCDs are only suitable for applications requires absolute low profile and low power consumption[1]. Several decades later, we all know what happened in the end. I think it was be fun to take a look at the LCDs at that time, are they really that bad? What it would be like to use that kind of screen in 2019?

    (A TFT LCD compared to a CSTN LCD, left: TFT, right: CSTN, both screen were from 90s)

    LCDs in the last century

    There were several different types of display being used on portable PCs last century. The very first portable PC in the last century usually comes with CRT displays, like Compaq Portable (1983) or IBM 5155 (1984).

    (IBM 5155, credit: Soupmeister, license: CC-BY-SA-2.0, source: https://www.flickr.com/photos/29012094@N07/5235790747 )

    Of course, it is clear that CRTs just too heavy to be used on these portable devices. Later they switch to TN LCDs, like on IBM 5140 (1986) and Toshiba T1000 (1987). These TN displays has very low contrast and very poor viewing angles.

    (Toshiba T1100 featuring a monochrome TN screen, credit: Johann H. Addicks, license: GFDL, source: http://www.addicks.net/gallery/Irgendwo/Toshiba_T1100_In_Betrieb)

    Later some companies experimented other technologies like Gas Plasma screens on Toshiba T3200 (1987) or IBM PS/2 P70 (1991). Gas Plasma screens provides perfect contrast, but the color was limited to different shades of orange, and was very expensive to produce. Finally, in the early 90s, the industry switched to the STN LCD screens. These STN screens provided not too bad contrast (typically 1:5 to 1:50), and few shades of gray. Given these laptops are mainly for business uses, STN screens was good enough. But what if one want color display? There were two choices, CSTN and Color TFT. The first laptop with a color TFT screen was the NEC PC9801NC, came out in 1990. The TFT screen provided much higher contrast ratio and much lower response time, with one drawback: it was expensive to manufacture. CSTN, on the other hand, was basically a STN screen plus a color filter. Cheap to manufacture but the performance was limited. As a result, STN and CSTN continues to dominate the market, and being used widely on low-end laptops. Today we can still see CSTN screens being used on New York subway trains.

    (This screen on MTA trains is a CSTN screen. Credit: Transit +PLUS)

    As you have already know from the title, this project focus on the CSTN screen, leave out early TFTs, monochrome TN, and monochrome STN screens.

    The CSTroN

    I have determined that I want to take a look at CSTN screens. The next question is how. Surely it is not hard to find a laptop with CSTN screen, and by just using that laptop I can get an idea what it is like to use a CSTN screen. So, I got myself a laptop from last century, powered by a AMD 5x86-P133 processor. Given the performance it has, things I can test are basically limited to DOS games. Surely there are many amazing DOS games out there, and I enjoyed playing them on that laptop. I wish to play some modern 3D games and watch YouTube videos on that screen and see how it behaves, but it is simply impossible.

    Or is it?

    The laptop limited what I can display on that screen, so I just need to get rid of that laptop, leave only the screen. I can then try to add a standard VGA or even HDMI port to that screen, and hook up whatever modern device I may want to.

    Actually it is a pretty common hack to mod a laptop screen into a VGA/HDMI monitor. The usual way of doing that is just buying a LCD driver board that match the screen, and hook the screen to the board. These driver boards...

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  • Demo!

    Wenting Zhang09/09/2018 at 18:47 0 comments

    Here is a demo! Playing BotW on a dual scan CSTN screen.

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