wargo@sdics.UUCP (04/11/87)
Hi there; To change the subject from lasers for a moment. I would like to know if anyone has any general knowlage on liquid crystals? Is the technology to a point that I can buy a sheet of the stuff or is it all custom work for watches, displays, etc... Can liquid crystals be made to work on a thin film. Are they binary or can they be make to be opaque? Thanks Dave ucbvax!sdcsvax!sdics:wargo Ice Cream, it isn't just for dessert anymore.
dennisg@fritz.UUCP (04/15/87)
In article <337@sdics.ucsd.EDU> wargo@sdics.ucsd.EDU (Dave Wargo) asks some questions agout liquid crystals. (sound of guy rummaging in dusty corners of his mind...) There are two flavors of liquid crystals. One type responds to changes in temperature, the other is affected by an electric field. Actually, any liquid crystal responds to both, but the material can be "tuned" for the desired application and performance. This is why the LCD display on the clock in my car gets really strange in hot weather. Temperature-sensitive LCDs change color, usually in a rather narrow range that is set by the particular formulation in use. They are widely available as a single spot sealed in stickers to be placed on components that heat up. If the color changes, the part is getting too hot. Thermometers are commonly made with several spots of LCD material, each tuned to a different temp range. I have such a thing on my fish tank, and they are available as fever thermometers, to be placed on the forehead. This material is sometimes available bound to sheets that can be cut to size with scissors. Look in the Edmund catalog. I have seen it as paint, too. Electrosensitive LCDs are normally scattered every which way. Under an electric field, the crystals line up in the same orientation. This does you no good at all unless you have an external light source so you can see what the crystals are up to. Commercially available LCD displays are either transmissive or reflective. In transmissive displays, the deactivated (disorganized) crystals appear cloudy as light passes through them. Adding an electric field lines up the crystals and allows light to pass with less scattering. You can make this work the other way by adding a polarized screen on each side of the display (polarized 90-degrees apart). Without the display between the screens, no light passes, as the polarizing screens block each other out. When you insert an activated display, the crystals line up, and do nothing to the polarized light, so it stays black. A deactivated display scatters the light, letting it pass back through the polarizing screen on the other side. A reflective display works the same way, but has a mirror on the back, and relies on light from the front of the display to make a round trip through the crystals. This means that you need brighter light to use it, but you can get better contrast because the light is getting two trips through the crystals for the price of one. It is becoming common to find transmissive displays illuminated in back by a flat (electroluminescent) panel. Makes for a nice display on a laptop or portable computer. >Is the technology to a point that I can buy a sheet of the stuff or is >it all custom work for watches, displays, etc... The electrosensitive stuff isn't a sheet. It is a liquid, imprisoned between two sheets of glass or plastic. The front inside surfaces of the display are coated with a transparent conductor that allows the application of the control field. LCD displays have traditionally been difficult to multiplex, so you usually end up with a solid (transparent) electrode on the back, and a complex tracery of electrodes on the front, making up the segments of the display. Each segment receives direct drive from some logic output. Much of the LCD displays running around are custom. There are generic LCDs around that you could design into an application. A quick look in the Newark Electronics catalog reveals products by Hamlin and IEE. Making your own LCD displays is possible. It can be instructive, but is not cost effective, and seldom pretty. There was an article in Radio Electronics (?) about 15 years ago with details. The basic procedure involves buying glass plates pre-coated with transparent conductor, removing what you don't want (with a heavy duty eraser), and pressing the plates together with a teflon gasket and the LCD liquid in between. They gave sources for all of the strange parts... >Can liquid crystals be made to work on a thin film. I need a better question before I can answer it. >Are they binary or can they be make to be opaque? I'm not sure what you mean by this question, but it looks like you want to know whether a LCD can have settings other than "on" and "off". Yes. The more field that you apply, the better (and quicker) the crystals will line up. There are points of diminishing return. But if you apply a weak field, you will get weak alignment. There's a better way to do it than this, however. You can feed the LCD with pulses. By turning it on and off fast enough, you can get pretty much any density you want. If the pulses go to the backplane electrode, the entire display can be adjusted for contrast. Up to now, I have led you to believe that LCD displays feed on DC. In fact, if you reverse the polarity of the field, the crystals do a quick about-face and re-organize pointing the other way. So they should be non-polarized... The nasty fact of the matter is that LCD displays will run on DC for only a short time before the display is burned in. You have to keep twitching the crystals around to keep them from falling into a permanently aligned state. The easiest way to do this is by applying a square wave signal to the backplane, and driving each segment from the same source through an XOR gate. +------+ +-------------------------- common | | | to backplane | osc. |--------+ ____ | | | \ \ \ +------+ +-----------| | \ direct drive ' | | XOR |------ to segment 'a' segment 'a' ----------------| | / control line . / /____/ | | ____ | \ \ \ +-----------| | \ direct drive | | XOR |------ to segment 'b' segment 'b' ----------------| | / control line / /____/ With a control line at logical 0, the segment drive follows the backplane drive, and the segment in question stays inactive. Changing the control line to logical 1 puts the segment out of phase with the backplane and it does its thing. If you really want the LCD display to last, you will take special to avoid all sources of DC bias, so the gates will be CMOS or some other family that drives output close to the power supply margins.
dennisg@felix.UUCP (Dennis Griesser) (04/16/87)
More info on LCDs, with a request for HELP at the end...
A couple of years ago, Sprague (the capacitor folks) was selling a small line
of liquid crystal displays in blister packs. I saw them at a couple of local
electronics shops. I remember 3 and 4-digit displays about an inch high.
High prices.
Jameco sells a line of experimenter's kits put out by Fairchild. Look through
their catalog for "Fairchild Technology Kits". One kit I remember had a 3.5
digit display, ADC/driver chip, and circuit board to make a digital panel
meter.
A quick look through old data sheets uncovered a couple of companies making
LCDs:
o Shelly Associates (Subsidiary of Datatron)
1562 Reynolds Ave
Irvine, CA 92714
(714) 540-9330
[stock instrument and digital clock displays, up to digits 1 inch high]
o Daini Seikosha Co., Ltd
31-1, 6-chome, Kameido, Koto-ku, Tokyo 136, Japan
(03) 684-2010
[stock small displays for watches, smaller assortment of larger clock
and instrument displays, a couple of graphics matrix parts]
o Hitachi
[a variety of character and graphic LCDs with attached decoding and
driving circuitry, simple micro-compatible interface]
Given the perversity of LCDs, you will never make space-efficient driving
circuitry yourself. Unless you are just hacking around, look for an LSI
solution. For anything more complex than a 3.5-digit clock or meter display,
look for companies selling LCDs mounted to driving boards.
---
Perhaps the worst way to experiment with this technology is to buy a
LCD/driver combo at an electronic swap meet, and plan on figuring out how to
use it. That's something that I did a couple of months ago, and it ain't
fun. Can anybody scrounge up a data sheet for me?
maker = Epson, electro-optical division
model = TCM A0010-3
HELP!
The screen is gray, with a chromed metal frame that binds it to the driving
circuit board. The driver contains 16 flat-pack ICs marked E-1120, and
another flat-pack with a different number. The external interface is a row
of 14 large gold plate-throughs, in the center of the bottom edge. The whole
thing is about a foot wide, and about 6 inches tall. Probably designed for
an Epson laptop computer. In case you didn't hear me, HELP!gnu@hoptoad.UUCP (04/17/87)
Thanks to Dennis Griesser for all the great info on liquid crystals. I have
a somewhat more immediate/practical question on them.
I'm interested in homebrewing a portable terminal including a liquid
crystal display, suitable for 80x24 characters or whatever I can get.
Got any good sources for these and the driver chips required?
Manufacturers' or distributors' names, cities, and part numbers would
be great, along with whatever comments you have from actually using
such devices. Like everybody else, I'm looking for low power, excellent
readability, and easy to drive screens :-).
All I need is quantity 1 -- if it ever works and becomes a product,
I'll be sure to let you all know.
I could always buy a laptop and disassemble it but that seems a waste
(of money and a laptop).
--
Copyright 1987 John Gilmore; you can redistribute only if your recipients can.
(This is an effort to bend Stargate to work with Usenet, not against it.)
{sun,ptsfa,lll-crg,ihnp4,ucbvax}!hoptoad!gnu gnu@ingres.berkeley.edudennisg@fritz.UUCP (04/17/87)
I just checked the Jameco catalog for the "Fairchild Technology Kits" that I mentioned in my last posting, and the line has changed hands. They are now called "Intersil Evaluation Kits". Now that I think about it, this change took place about ten years ago... 7106EV/kit 3.5-digit single-chip ADC/driver, PCB, display $49.95 The parts are also available individually: FE0202D .5-inch, 4-digit LCD $12.95 FE0203D .5-inch, 3.5-digit LCD $12.95 7106CPL Intersil 3.5-digit single-chip ADC/driver $9.95 7116CPL Intersil 3.5-digit single-chip ADC/driver, w/hold $9.95 7211IPL Intersil 4-digit LCD driver, TTL-compatible $6.95 7211MIPL Intersil 4-digit LCD driver, micro-compatible $7.49 7224IPL Intersil 4.5-digit counter/driver $12.95 The address is Jameco Electronics 1355 Shoreway Rd. Belmont, CA 94002 (415) 592-8097 [ no, I don't own any of their stock :-) ]
henry@hpcvci.HP (Henry Nielsen) (04/19/87)
> I'm interested in homebrewing a portable terminal including a liquid > crystal display, suitable for 80x24 characters or whatever I can get. > Got any good sources for these and the driver chips required? > Manufacturers' or distributors' names, cities, and part numbers would > be great, along with whatever comments you have from actually using > such devices. Like everybody else, I'm looking for low power, excellent > readability, and easy to drive screens :-). > > All I need is quantity 1 -- if it ever works and becomes a product, > I'll be sure to let you all know. > > I could always buy a laptop and disassemble it but that seems a waste > (of money and a laptop). > -- > Copyright 1987 John Gilmore; you can redistribute only if your recipients can. First, some background information: There are three types of liquid crystals: smectic, nematic, and cholesteric. Smectic LCs line up in a fundamentally 1-dimensional ordering. Nematic LCs line up in sheets (2-d ordering) and have an orientation that can be controlled by an extermal electric field. These are the ones that you'll find in LC displays. Cholesteric LCs also line up, but their key property derives from their helical structure - they reflect light at the wavelength equal to the pitch of the helix. This pitch is controlled by the ambient temperature and is EXTREMELY sensitive. O.K. So much for background. Don't try to make a LC display. In principle it is very easy, in practice quality control will keep you up nights, making you unpopular with you neighbors... :-) Seriously, there are little problems like control of static-electric fields on the inside of the glass plates enclosing the LC material, proper sealing (they don't work well if moisture gets inside), etc. So, the best way to use such a display is to buy one. Now, in quantities of 1, I'm not aware of anyplace you could get a Japanese display (I'm pretty sure they've wiped out any other American manufacturers...). Also, these displays take about 10 volts to drive (15V is better), and that makes the display drivers a little tricky. For low power, you want CMOS drivers. For Hi-res, you need lots of data handling capability in the drivers - this means very small geometries on the chips - and this means thin gate oxides and that spells out a problem because you now have 10 volts across a (nominally) 400 Angstrom gate oxide. This makes a E-field of ~2.5 Megavolts/cm and requires a very high integrity gate oxide... In English - you probably can't find a source for these (we make them, but don't sell them outside the company...). As for readability - I'll assume you mean a wide viewing angle - don't hold your breath. Even with tricks like lenses in front of the display AND backlighting, its very tough to improve the performance you see in current LC display products. Bottom line: It sounds like an interesting project. I don't think you'll be able to find the materials you need to put it together (I'll be happily surprized if you do). Your best bet is, most probably, to buy a laptop like the HP Portable Plus or the Toshiba 1100+ (I know the HP is good and has a reasonable terminal emulator; I've only heard rumors about the Toshiba unit, but what I have heard is positive and I do know that they're quite competent at IC manufacturing so that the reliability should be acceptable - I assume that they have an on-board terminal emulator...). Disclaimer: This is really NOT intended as a sales-pitch for laptops. Henry Nielsen Hewlett-Packard Company, Corvallis Oregon. hplabs!hp-pcd!henry
kavaler@ucbcad.berkeley.edu (Robert Kavaler) (04/20/87)
A good place to get liquid crystal displays is from Hitachi or Sanyo (Hitachi is cheaper for the 24x1 display). Both companies offer a wide range of display sizes with both graphics and text. I suggest you order a catalog to get the right one. I would also suggest that you get the premade "Display Modules" which include both the display and the LSI controller. Generally the interface to the controller is a 4/8 bit microprocessor compatible I/O interface, although serial interfaces are also available. The power supply required vary depending on size and features, but mainly 5V is required. Large displays (i.e. full screen) also require either -12 or 20V supplies (depending on manufacturer). All of these the displays use the same controllers (made by Hitachi which probably explains why Hitachi is cheaper). For more info. on Sanyo contact DeAngelo, Rothman & Co. Inc, (213) 827-2202. For more info. on Hitachi contact Hitachi Electron Tube Division (408) 435-8300. There are other people who make these displays, including some American manufacturers (although I'm not sure how much is actually made in the U.S. since I noticed that many modules are IDENTICAL except for price) Robert Kavaler (kavaler@oz.berkeley.edu) P.S. I do not work for nor represent any manufacture and offer advice free of charge. Remember, you get what you pay for.
dennisg@felix.UUCP (Dennis Griesser) (04/22/87)
In article <1998@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes: >I'm interested in homebrewing a portable terminal including a liquid >crystal display, suitable for 80x24 characters or whatever I can get. ----- For something this size, forget trying to make your own driver. >All I need is quantity 1 -- if it ever works and becomes a product, >I'll be sure to let you all know. The are only two ways to get something this fancy for cheap: o visit swap meets, check liquidators o take apart a cheap laptop The quantity-one price, new, retail, of such a display and driver might well be more than the cost of a cheap laptop. >I could always buy a laptop and disassemble it but that seems a waste >(of money and a laptop). Maybe not. You said you want to build a "portable terminal". That means that you can salvage: o display o keyboard o case o batteries & power supply o (maybe the CPU and memory, too) Look for a really cheap unit. Would the display on a Radio Shack Model 100 make you happy? You can get those computers for a couple hundred bucks. Comes with a terminal emulator in ROM, serial port, and internal MODEM... Many months ago, perhaps as long as a year, I saw pieces of the Convergent Workslate at a local electronics swap meet. Not a bad looking item. They wanted about $20 for enough pieces to put one together. Perhaps you can find one in the back of ComputeameAg> 3 Hosi
dennisg@felix.UUCP (Dennis Griesser) (04/30/87)
In article <1998@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes: >I'm interested in homebrewing a portable terminal including a liquid >crystal display, suitable for 80x24 characters or whatever I can get. In article <4255@fritz.UUCP> I replied: >For something this size, forget trying to make your own driver. >... > o visit swap meets, check liquidators > o take apart a cheap laptop While flipping through last month's Computer shopper, I found an ad for D. L. Liquidators 1970 S. West St. Suite 345 Wichita, KS 67213 (800) 255-1382, ext 136 - ORDERS (316) 942-0990 - INFO They folks offer: o KYOTRONIC 85 $149.95 ($599.95 list) CMOS 8085 CPU 32K ROM, including BASIC, text editor, and terminal emulator 16K RAM, expandible to 32K RS-232 interface Centronics printer interface cassette interface looks like a Radio Shack Model 100 o NEC PC-8401A $399.95 ($999.95 list) CMOS Z80 CPU 96K ROM, including "bios", terminal emulator, filer, Wordstar, and a spreadsheet. ROMs are in three sockets, and can be swapped. (it looks CPM compatible) display 80 characters x 16 lines fold-open laptop Does this sound close to what you want?