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Any ideas for lighting up an LCD without a backlight?
I guess the LEDs would have to come from the front or sides or something, but usually there is a lot of glare with that as the LED reflects in the LED glass as well as lights it up.
Since glare is polarized horizontally, try illuminating it with non-polarized light and wear sunglasses to view it. You might even just illuminate with 45° polarized light and avoid most of the glare without the sunglasses.
Since glare is polarized horizontally, try illuminating it with non-polarized light and wear sunglasses to view it. You might even just illuminate with 45° polarized light and avoid most of the glare without the sunglasses.
Yeah that makes sense. I'll have to see if i can find my roll of polarizing film to try it.
I dont think i really want to have to wear sunglasses though, but that also gives me some ideas.
hi Al.
I have successfully used edge lighting with 'reflective' LCD displays on a number of products.
Used 6V, 'wheat corn' sized wired tungsten lamps under run at 5V, one at each end of the LCD, obviously the lamp is blanked off from direct view of the user.
This is interesting. So you are basically saying that low level light is the way to go, and position it (and hide the source) correctly?
I'll have to try that.
Interesting, i tried using the back light from another defunct display, but it wasnt enough light and hard to position correctly. It was a little shorter than the current one i am using anyway.
I also checked that any light coming from the back does not show up at all through the front.
I believe that is because the polarizing filters in the unit are crossed. Thus, only light that has been rotated gets out. The Wikipedia article shows the filters as horizontal and vertical, but other sources show that both filters are rotated 45° in current displays (https://en.wikipedia.org/wiki/Liquid-crystal_display ).
Yeah, and also there is a PC board attached to the very back of the LCD display itself
Here is a screen shot of the LCD in action. It lights up nice with the right lighting. In this pic, the cam flash is the only light.
I might take your idea about the sun glasses and modify it slightly and see what happens...
Take a sheet of polarizing film and place it in front of the display, about 1/4 inch out in front away from the front of the LED glass itself. Keep in mounted like that, then shine LED's in from the sides (hopefully, as it is a bit long) or from the top and bottom.
You might recognize this display from the web. It's the Wintek 24 x 1 LCD non backlit which sold in some places for one dollar USD. It's hard wired for 8 bit parallel transfer though, so that is a down side. It has to be interfaced with at least 7 bits plus 2 more unless you dont mind making up your own hardware interface with say the 74xx164 shift register or similar.
A FEW MINUTES LATER:
Ok i could not find my polarizing film because i dont have it cataloged. What i did find though was a high quality polarizing filter. I have now learned that it is not so much the glare (usually present) than the angle that the LED has to be mounted in order to make a difference in the display lighting at all. It has to be at a very large angle from the display front, which means it would have to be like 4 inches in front of the display.
Also, rotating the filter would either allow the display lettering to show or completely blank it out (as we would expect) but unfortunately it did nothing for the glare, when the light is shining on such an angle that there is glare that is. The glare comes mainly from the eye angle and the LED angle, which if not ideal, causes glare. So to get rid of the glare it looks like it only takes mounting the LED at the right angle. The problem is though that the angle to get any light at all is way too large, meaning at least for this display it cant be lit from the two ends nor the top or bottom, at least with LEDs that are very close to the display. They have to be way out in front, similar to regular room lighting. What a shame.
I like these displays because they have a decent font and after all i have quite a few of them not being used yet
Most of the non illuminated LCD's I have, actually have the connections to add a led light to the board. The leds are oblong and thin and normally illuminated from the sides/edge, some LCD's have one edge with a kind of 'blob' of glass one end, light from the other end or you get bad glare.
There is a post somewhere on here from years ago where I wanted to put some red leds in a non illuminated LCD, its worth noting that most LCD's are made the same, so those without lights are the same with those with lights. In other words there is normally little reason why you cant add a light, I like erics idea of a non led light but I do know you can buy cheap leds for lighting LCD's now, ebay and china are my normal supplies for these
Well this LCD has no inlets for light on any side or top or bottom. Any angle does nothing.
The only hope is maybe after pulling off the frame and checking to see if it will light up then, and then replacing the frame after cutting one or both sides off, or top and bottom off. I'll have to get to that. It means that if it does not go back together right it wont ever work again though.
LATER:
I took the frame off, and i can see what is happening. There is a clear strip under the character layer, and this strip transmits light from one end to the other. If i took the character layer off i could probably light up something such as characters drawn with a magic marker. The trouble is that the character layer is completely opaque so no light gets through. That's the real problem. It must be made such that it does not allow light to shine through it. I believe this is called a 'reflective' LCD panel.
**broken link removed**
The only hope now would be to try to mount LEDs out from the front pointing back toward the front. That will stick out quite a bit though unless the panel is recessed significantly.
you probably know this but the LED unites are normally square, the end bit in your photo with the bulbous bit is, thats where the LED lights on mine are. I will try and get you a pic tomorrow it might help, I also think I have one of those LCD's so I might try and see if I can take a light off another and make it work on one of those, the LED are also alot brighter than the normal 20mA ones, I think mine are 300mA but will need to check
Well, what i saw was a clear strip of plastic that transmits light very well, and it was behind the glass of the display where the characters show up. What happens though is absolutely no light gets through the back of the glass, not even a hint of light.
A possibility may be that there is some foil directly behind the glass and that is stopping the light from getting through. If the foil could be removed it might backlight after all, but getting that foil (if that is what it is) out means breaking the connection between the glass and the elastomeric connector. Getting that back together again and working is not easy because sometimes those connectors never make a good connection again, until they are replaced.
To get a better picture of how it is layered:
sheet of light conducting clear plastic,
foil on top of that,
glass display on top of that (where the chars show up),
frame around the edges of that.
The leds normally shine through the side they are like a square sealed unit with the light directed straight ahead, i will need to try and get a pic, i tried with other leds but only the square ones worked. I can see the opening on yours at the side where mine has the LED
Yes you are right, that has a small opening on one side, but i tried shining light from many angles and it did not light anything up. When i took the frame off i could see that the light could make it's way BEHIND the display glass, to the other end, but no light comes through the display itself. And i think i know why now.
I had another LCD from years back taken apart already, not to examine it, but because it came apart one day when i was troubleshooting a digital meter. It came off of the elasto connector and so i could see the whole thing.
Looking at it carefully, i can see that the back of the glass has a metalized coating. It is probably aluminum. I think it is deposited there when the LCD is manufactured. This coating prevents any light whatsoever from getting through the display character area.
This is what now leads me to believe that some displays can never be backlit properly.
I plan on taking this very display apart completely at some point, because i have other ones around. I'll use this one as a test. If you want to show pics of other displays too though that would be cool. We can compare them to this one. I'll post pics too.
What i havent tried yet is lighting it from the edge through the glass itself, which would not be a backlight but a "frontlight". I doubt it but it's worth a shot.
Ok I am right and wrong at the same time!
two pics.
This is a 40 character 4 line LCD and has a LED backlight as you can see, it goes right under the unit. the next pick is a 16x2 lcd and show a different LED unit that also light the back, but this is the led unit I have taken off and shone through the glass bulge bit on another unit. I have one of the same LCD's you have and one I have modified with a different LED, both are in the draw in my dads workshop........... I tried to go get them tonight to photograph but didnt make it inside (sorry) I will do it tomorrow, I just couldnt open the door tonight but tomorrow I will be ready
Hi Al.
If you are lucky, and I have a same size display with built-in backlighting, I will send it to you for direct replacement.
Number of characters ? Dimensions ? Hitachi controller ?
LG:
Thank you for the photos, i will study them and compare to my display. I am also thinking about taking one completely apart so i can solve this mystery once and for all, regardless if i can get it back together or not.
Miguel:
Thank you for the offer. This one is 24 x 1 line. It uses HD66717 controller. One of the problems is the backlight, the other is that it is HARD WIRED for 8 bit parallel operation, even though that controller is capable of I2C control, and it is impossible to get to the wiring because it is under the COB chip (unless of course you know a work around).
One of the reasons i was trying to get this lit up was because it is hard to see without some light, and i have a few of them so i thought i could use them for various stuff.
What kind of displays to you have on hand, and what color backlight?
I hate to put you through that much trouble though. I do have a display that is backlit and am getting another one, but i like these little displays because they are so narrow. They can fit in a package probably about the size of a cigar or maybe a little bit wider so that means they can be used in a hand held pen-like probe.
OK.
Am attaching a picture of what I have, note several are in their antistatic bags. Center top (white) is a backlight that slides under the LCD. Color is likely green, and I have more of those 'backlight only' but just moved and my stuff is boxed and my brain is not functioning right with so much to do and remembering what is where.
I could send several for you to try, keep what you need. My workbench is non-existant right now in order to find which is what.
Added: The rear glass has a silver film for reflective type displays, and no film for the ones fitted with the backlight 'bar' under it.
The backlight 'bars' are 5 3/4" long x 3/4" wide and 1/8" thick, with +,- solder pads.
Found the controllers have a vendor sticker on top; but likely Hitachi 44780
Good instructionals on the silver backfilm removal, adding backlight :
----> **broken link removed**
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