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.
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. 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)
in the last century
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
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.
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)
you have already know from the title, this project focus on the CSTN
screen, leave out early TFTs, monochrome TN, and monochrome STN
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
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.
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