If you were tasked with designing a color video monitor, it’s pretty clear how you’d go about it. But what if you’d been asked to do so 20 years ago? Would it have been a cut and dried from an engineering standpoint? Apparently not, as this hybrid LCD-CRT video monitor demonstrates.
We’d honestly never heard of this particular design, dubbed “LCCS”, or liquid crystal color shutter, until [Technology Connections]’ partial teardown of the JVC monitor and explanation of its operation. The idea is simple and hearkens back to the earliest days of color TV in the United States, when broadcasters were busy trying to bring color to a monochrome world in a way that would maximize profits. One scheme involved rotating a color wheel in front of the black-and-white CRT and synchronizing the two, which is essentially what’s happening in the LCCS system. The liquid crystal panel cycles between red, blue, and green tints in time with the CRT’s images behind it, creating a full-color picture. “But wait!” you cry. “Surely there were small color CRTs back in the year 2000!” Of course there were, but they kind of sucked. Just look at the comparison of a color CRT and the LCCS in the video below and you’ll see why this system carved out a niche in the pro video market, especially for video assist monitors in the days before digital cinematography. A similar system was used by Tektronix for color oscilloscopes, too.
As usual, [Technology Connections] has managed to dig up an interesting bit of the technological fossil record and present it in a fascinating way. From video on vinyl to 1980s copy protection to the innards of a toaster, we enjoy the look under the hood of forgotten tech.
21 thoughts on “Monochrome CRT And Liquid Crystal Shutter Team Up For Color Video”
Sounds similar to the display on some of the TDS range of Tektronics scopes!?!
Doh watched it all and he explains that !
Yes, and Hackaday even had an article about Tektronics NuColor earlier this year: https://hackaday.com/2019/01/17/sharpest-color-crt-display-is-monochrome-plus-a-trick/
I remember the first time I have seen one of those, I actually thought it was DLP based on the way it shimmered.
Many years ago, there was a tablet that used a monochrome LCD with a RGB backlight, the idea being that it would only need 1/3 the power for backlight due to no filter losses and it even had an “ebook mode” that disabled the backlight entirely and relied on ambient light for illumination. I think the biggest problem is that refreshing the LCD that fast was difficult to do and cut into the power advantage in color mode.
Any pointers on what that device was? It would be interesting to do a teardown on one…
This device works on the same principle https://www.youtube.com/watch?v=q1LvleZcJm0
Interesting. I assumed that stuff like that just used a different colour filter over the part of the display that needed that colour, as each element has a fixed colour of display.
Field Sequential Color LCDs (FSC LCD or FS LCD) based on alphanumeric/segmented LCDs are made by Winstar, Powertip, Orient Displays and others. They seem to be 8-color only.
Tektronix did this for a bunch of products back in the 70’s, 80’s & 90s. They had LCD shutters to add color to monochrome oscilloscopes and logic analyzers, and later to make stereoscopic color helmet mounted VR displays. The VR displays are neat; they’re <1" CRTs with a res of 800 x 600. They wouldn't have been able to achieve that resolution at that size with a color CRT, so they ran the CRT at 180 FPS, and used an RGB shutter in front. I have a pair (serial #000001!), but haven't been able to generate the correct video signals to make them work yet.
/back in the day they did some weird things with CRT tech to get round such problems . I have a Marconi testset and it updates from Left to right not top to bottom because that is better for the scope functionality!
180 refresh may be selectable on some SGI workstations, 180 was used to drive some VR displays for stereoscopic.
Holy moly! Now THAT is a piece of interesting tech history! You have to tell me how that video signal search is going! How on earth did you find one? Let alone #00001!
Oh man, I’m embarrassed to say I got distracted by other things, and the set is back in storage. I don’t think they made all that many, but the pair was given to me by one of the more prolific Tektronix collectors.
VR displays? What were they used for? Is this like a professional design tool type thing for use with a PC? I only really know about the W industries Virtuality arcade game machines but I’m pretty sure those use completely LCD displays and are much lower res than that anyway, other than a couple of mid 90s PC sets like the forte vfx2 or whatever it is called (I think I blended the names of two of them together), which are also designed primarily for games afaik and are LCD. Of course on that topic another cool display technology is what the Nintendo Virtual Boy uses which comes from a head mount single eye PC monitor called the private eye apparently, which has a column of LEDs that scans left and right with a mirror.
Here’s a link to the CBS colour system,
Click on the film of the colour system test, but for the love of God don’t buy it!
Are any shutters like these currently available?
You can harvest one out of say an LCD laptop screen. Usually those are translucent LCDs with a backlight diffuser panel behind them. Toss the backlight diffuser (or use it as a light box for tracing, or as a nice diffuse daylight lamp) and put the LCD in front of a CRT—et voila. You get the nice deep black levels of a CRT, the sharpness, by basically using a B&W light source that displays the video’s luma channel instead of just filling the whole frame with bright white light.
You’ll lose a bit of brightness using that kind of panel, though. You gain a bit by using a monochrome CRT with no shadow mask, so at least some of that will be offset.
It’s not quite the same, modern LCD panels have millions of rgb pixels each with RGB subpixel liquid crystal cells. The filters used for this are single liquid crystal cell panels, no RGB. They do still make them like this but only quarter-sized for scientific optics related stuff. They’re even electrically adjustable to only let through whatever frequency of light you want (within a range of course) (Liquid Crystal Tunable Filters)
So, basically an lcd screen with crt display as backlight?
It’s more like a CRT screen with an LCD color filter. The LCD is just one large “pixel” that changes between Red Green and Blue at 3x the standard refresh rate, allowing the CRT to draw each color channel in greyscale and then filtering it to the right color so fast you can’t tell.
Oh, that makes sense. Thanks for the clarification!
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