Post by thread:[EE] Backlighting panel LCD

part 1 1355 bytes content-type:text/plain; (decoded 7bit) I'd like to LED backlight a 4-digit LCD and wonder if anyone has suggestions/comments or done anything similar The first problem is that there's only 2mm between the top of the driver IC (40 pin DIP) and the bottom of the display. I've tried several types of LEDs and diffusing material (translucent acrylic, white plastic, patterned shower plastic) but the gap is so narrow hat the beam doesn't really have room to spread out. The best result was a blue or white LED off to end sides about 20mm away at a shallow angle. But I don't have room in the case to do that unfortunately. Pity, looks good. Any closer and the brightness of the LED highlights the "off" segments. Can't raise the LCD as there's a limit on both case depth and actuator length of the push- buttons I want to use Ideally I'd like some diffuser that magically can spread the light out evenly from several point sources Another option is to put the driver on the other side of the PCB. The connections between the IC and display are simplest as shown in the picture. To keep that simplicity, the pins of the IC would have to be bent up so that the top of the IC is against the bottom of the PCB. I worry about whether this would cause premature failure (if so, how premature ?) of it because of some kind of damage to the pin/body seal part 2 414 bytes content-type:image/gif; (decode) part 3 35 bytes content-type:text/plain; charset="us-ascii" (decoded 7bit)

Hey Jinx, have you taken apart a pre-backlit LCD? The ones I've seen have a plexiglas panel under the LCD. The panel is side lit with LEDs, and the back side of the panel (the one farthest from the LCD has a pattern of small white dots. Hope that helps. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams On Sun, 26 Dec 2004 01:54:23 +1300, Jinx <spam_OUTjoecolquittTakeThisOuTclear.net.nz> wrote: {Quote hidden}> I'd like to LED backlight a 4-digit LCD and wonder if anyone > has suggestions/comments or done anything similar > > The first problem is that there's only 2mm between the top of the > driver IC (40 pin DIP) and the bottom of the display. I've tried > several types of LEDs and diffusing material (translucent acrylic, > white plastic, patterned shower plastic) but the gap is so narrow > hat the beam doesn't really have room to spread out. The best > result was a blue or white LED off to end sides about 20mm away > at a shallow angle. But I don't have room in the case to do that > unfortunately. Pity, looks good. Any closer and the brightness of > the LED highlights the "off" segments. Can't raise the LCD as > there's a limit on both case depth and actuator length of the push- > buttons I want to use > > Ideally I'd like some diffuser that magically can spread the light out > evenly from several point sources > > Another option is to put the driver on the other side of the PCB. The > connections between the IC and display are simplest as shown in the > picture. To keep that simplicity, the pins of the IC would have to be > bent up so that the top of the IC is against the bottom of the PCB. I > worry about whether this would cause premature failure (if so, how > premature ?) of it because of some kind of damage to the pin/body > seal

FWIW My best homebrew was taking a piece of acrylic or plexi (perspex?) lighting from both sides with leds after stuffing in behind the LCD. (I think it was white paper behind that.) Sanding the acrylic to diffuse (and force the light to leak at the scratches?) was key. HTH D Jinx wrote: {Quote hidden}> I'd like to LED backlight a 4-digit LCD and wonder if anyone > has suggestions/comments or done anything similar > > The first problem is that there's only 2mm between the top of the > driver IC (40 pin DIP) and the bottom of the display. I've tried > several types of LEDs and diffusing material (translucent acrylic, > white plastic, patterned shower plastic) but the gap is so narrow > hat the beam doesn't really have room to spread out. The best > result was a blue or white LED off to end sides about 20mm away > at a shallow angle. But I don't have room in the case to do that > unfortunately. Pity, looks good. Any closer and the brightness of > the LED highlights the "off" segments. Can't raise the LCD as > there's a limit on both case depth and actuator length of the push- > buttons I want to use > > Ideally I'd like some diffuser that magically can spread the light out > evenly from several point sources > > Another option is to put the driver on the other side of the PCB. The > connections between the IC and display are simplest as shown in the > picture. To keep that simplicity, the pins of the IC would have to be > bent up so that the top of the IC is against the bottom of the PCB. I > worry about whether this would cause premature failure (if so, how > premature ?) of it because of some kind of damage to the pin/body > seal > > > > ------------------------------------------------------------------------ >

> Hey Jinx, have you taken apart a pre-backlit LCD ? No, I haven't, not got one to pull to bits. Did wonder how it was done. I don't recall ever seeing a glass LCD (eg multimeter type) being backlit. Display area of these is about the size of a 16x4 > The ones I've seen have a plexiglas panel under the LCD. The panel > is side lit with LEDs, and the back side of the panel (the one farthest > from the LCD has a pattern of small white dots > > Hope that helps. Does, very interesting. Are the "white dots" actually painted or pits moulded into the plastic ? I remember from my art and craft days making cuts and holes into clear resin rods to make light come out at the cut/hole. I was thinking some kind of pipe/guide with diffusing features would work. Could be made from rod or sheet or some combination, although I've got several dozen to do and don't want it too complicated. A (simple) assembly or millable pattern is OK Another thought was to paint either the underside of the LCD or any acrylic sheet with phosphorescent dye and use UV LEDs in the hope that the lit colour would spread out that way, but I've no proof it would Here's an explanation of the different types of display vis-a-vis how the characters are seen http://www.pacificdisplay.com/lcd_polarizers.htm The actual LCD I'm using is a Displaytech equivalent of the Varitronix VI-402 transflective. Maybe I could light it from the front. The case is 2mm black plastic into which I'll mill a cut-out. Then use a piece of 3mm acrylic with a 2mm flange milled around the edge. It's possible that 1mm of acrylic edge inside the case could be lit One other thing - why am I up at 7am on Boxing Day fussing about how to backlight an LCD ? ;-)))

John and Dave Thanks for suggestions. The idea of using white paper as both reflector and diffuser is worth trying. It may be that shining the LEDs down onto a reflector would look better than shining up directly onto the back of the LCD I think I'll have a look also at moving the driver IC to get more room under the display so that light has more chance to break up and spread, and I can be choosy about their orientation. A reflector/diffuser will still be useful Not especially keen on bending pins backwards on a big DIP but I've a few scrap boards with never-going-to-be-used 40- pin ICs that I can experiment with The alternative is to draw the board with the more complicated layout and use plenty of vias to get the IC on the other side of the PCB without needing to bend pins. ISTR that vias don't add greatly to the cost of the PCB although I've never had a board made with them. I did ask at my board house a couple of years ago and remember being not too shocked but the board I had made need just a few through-holes that got connected with pins and wire so I didn't worry about plated vias Impossible to get a pricing at this time of year - can someone give me an idea of what the addition of say 40-50 vias would do to the cost of a board ? Obviously a hole is needed for each but what about the plating ? I believe my board house always starts with double-sided stock if that's relevant

The white dots were just painted on. Actually, probably a silkscreen. It really works well, especially when you put some reflecting tape around the edges of the piece of plexi (we were playing with 3/16" thick material) whereever there are no LEDs. We were really amazed...no one though that just adding some white dots would work. We even tried just painting the whole back white...I think that worked pretty well too, though I don't remember exactly. It's pretty easy to experiment though, just a piece of plexi with different patterns in different regions. Toss something on top to check out the evenness and perceived brightness. I'm not so surprised you are up at 7AM on boxing day fretting about this...you were up last night fretting about non demoninational holiday greetings :) Oh, and the via thing...a via is just another plated through hole. Would your board house charge you if you had a board with another 50 holes in it? Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams On Sun, 26 Dec 2004 08:28:15 +1300, Jinx <joecolquittKILLspamclear.net.nz> wrote: {Quote hidden}> > The ones I've seen have a plexiglas panel under the LCD. The panel > > is side lit with LEDs, and the back side of the panel (the one farthest > > from the LCD has a pattern of small white dots > > Does, very interesting. Are the "white dots" actually painted or pits > moulded into the plastic ? I remember from my art and craft days > making cuts and holes into clear resin rods to make light come out > at the cut/hole. I was thinking some kind of pipe/guide with diffusing > features would work. Could be made from rod or sheet or some > combination, although I've got several dozen to do and don't want it > too complicated. A (simple) assembly or millable pattern is OK > > Another thought was to paint either the underside of the LCD or > any acrylic sheet with phosphorescent dye and use UV LEDs in > the hope that the lit colour would spread out that way, but I've no > proof it would > > Here's an explanation of the different types of display vis-a-vis how > the characters are seen

Josh, thanks for info re dots and reflecting. I'll get some stuff together and make an evening of it > I'm not so surprised you are up at 7AM on boxing day fretting about > this...you were up last night fretting about non demoninational > holiday greetings :) Hmmm, oh yeah (Christmassy related - gave my nephew, a big Iron Maiden fan, a "Grim Reaper plasma ball". Took him all of two minutes to discover if he put his hand all over it he could shock his sister with the other, the little monster ;-)))) ) > Oh, and the via thing...a via is just another plated through hole. > Would your board house charge you if you had a board with another > 50 holes in it ? Yes. I'd expect a charge for the hole of course but I've no idea how much the plating of the vias is. If I can get satisfactory backlighting with the components as they are then the cost of vias would be academic (for now)

I've come up with solution that's easy, repeatable and looks great. In the next day or so I'll organise pictures I took a piece of 2mm acrylic and covered one face, one end and both long sides with adhesive aluminium foil. The open face is under the LCD. A dab of clear silicone should be enough to hold it. A 5mm white LED is shone into the open end. The effect is an even, cool blue-ish light. Looks "just like a bought one". "on" segments stand out very well and "off" segments can't be seen at all. Tried it with super- bright red and green but white is better. Got some coloured film around here somewhere, will try that over the powerful white LED rather than a less powerful coloured LED

> I've uploaded some initial pics and a short description > > http://home.clear.net.nz/pages/joecolquitt/led+lcd.html What LED current / power are you using? What is the display area? I'm interested in the possibility of extending that to a somewhat larger display. If you used a single LED on a larger display, does it seem hat you would get a similar illumination? (Obviously available illumination per area will drop but the effect may be acceptable). How much more area seems likely with a single LED? RM

> What LED current / power are you using? 5mm white, 5V, 100R series 2mm green, 5V, 270R each (worked better than I expected) > What is the display area? Whole glass is 50x25. Cutout area in pictures, 44x18 > I'm interested in the possibility of extending that to a somewhat > larger display. > If you used a single LED on a larger display, does it seem that you > would get a similar illumination? It helps if you can get the LED further back. I'm very limited in that regard and have to tone down the bright area right in front of the LED. Have only one type of white and that has a fairly narrow beam. Coloured LEDs I have in all varieties I have but a small selection only of ones with decent output. Red is the only colour that doesn't really look too good. A bicolour red-green would be useful if SB or UB were available. Green for normal, red for alarm or whatever, but you could do it with singles > but the effect may be acceptable). How much more area seems > likely with a single LED? As above, really good if you've room

Looks good Joe. Just so you know, you can clean up the cut edges of the plexi by heating it (carefully) with a hot air gun. If you go slow and are careful they come up to a nice clear polished-like look...with no polishing! How much would you pay for this! But wait, there's more! Uh...ok, time for bed. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams On Mon, 27 Dec 2004 13:27:28 +1300, Jinx <.....joecolquittKILLspam.....clear.net.nz> wrote: > I've uploaded some initial pics and a short description > > home.clear.net.nz/pages/joecolquitt/led+lcd.html > > Promising. I'm impressed with the look of the white

> Looks good Joe. Just so you know, you can clean up the cut > edges of the plexi by heating it (carefully) with a hot air gun. If > you go slow and are careful they come up to a nice clear polished- > like look...with no polishing! That I didn't know. I'm short of a hot-air gun and will try that as soon as I replace the one that died. I'll also make a couple of identical test rigs to compare results. As this is for a run for sale ASAP I'll need to get a wiggle on. Will report back some time soon

At 12:05 AM 28/12/2004 +1300, you wrote: > >That I didn't know. I'm short of a hot-air gun and will try that as >soon as I replace the one that died. I'll also.... Be careful to set the hot-air gun down very gently after use. The filament breaks too easily from shock. Also put down with nozzle facing upwards for convection cooling, otherwise the thermal cut-out switch cooks and takes ages to release. ..just my expreience leading to the demise of my beautiful Ryobi heat gun. Regards Roland Jollivet

Oh, one thing I forgot to mention is that until you get a feel for it, you might scorch the plastic, so be careful. Making the edges smooth really helped the light get into the plexi in the one I played with. A lot less lost than the rough cut edge. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams On Tue, 28 Dec 2004 00:05:29 +1300, Jinx <EraseMEjoecolquittspam_OUTTakeThisOuTclear.net.nz> wrote: {Quote hidden}> > > Looks good Joe. Just so you know, you can clean up the cut > > edges of the plexi by heating it (carefully) with a hot air gun. If > > you go slow and are careful they come up to a nice clear polished- > > like look...with no polishing! > > That I didn't know. I'm short of a hot-air gun and will try that as > soon as I replace the one that died. I'll also make a couple of > identical test rigs to compare results. As this is for a run for sale > ASAP I'll need to get a wiggle on. Will report back some time > soon

Roland wrote: >Be careful to set the hot-air gun down very gently after use. The filament >breaks too easily from shock. Also put down with nozzle facing upwards for >convection cooling, otherwise the thermal cut-out switch cooks and takes >ages to release. >..just my expreience leading to the demise of my beautiful Ryobi heat gun. > > OTOH, I've had a cheap, no-name offbrand heat gun for over five years now, and have dropped it on my cement basement floor countless times. For another fair bit of abuse, I occasionally block the air intake briefly to speed the heat-up. <grin> Anyhow, I guess it pays to take care of it if you actually spend some $$ getting it... I think I picked mine up for ~$15 - not worth preserving for any length of time. - Robert

On Dec 27, 2004, at 3:05 AM, Jinx wrote: >> Just so you know, you can clean up the cut >> edges of the plexi by heating it (carefully) with a hot air gun. > That I didn't know. I'm short of a hot-air gun An open flame will work, if you're careful. Perhaps better. IIRC, TAP plastics (who does custom fabrication) has three grades of "edge finish." there is the straight "routed" edge (as it comes off the CNC router, I guess), a "flame polished" edge, and a full mechanical polish... taking apart a laptop lcd backlight can be very educational. There's a lot of interesting mechano-optical components in there that combine to get an even backlight out of an edge-illuminated thing. Not that applicable to the small display you're using, but interesting. BillW

> >> Just so you know, you can clean up the cut > >> edges of the plexi by heating it (carefully) with a hot air gun. > An open flame will work, if you're careful. Perhaps better I think I'd try sandwiching the acrylic between two bits of metal plate or wood with just the rough edge showing, to limit the ingress of heat and prevent any slumping or deformation. Could have a go with a butane torch while I haven't got an air gun > full mechanical polish... Maybe I can do something with a fine sanding + buffer wheel on the lathe ? > taking apart a laptop lcd backlight can be very educational. > There's a lot of interesting mechano-optical components in there > that combine to get an even backlight out of an edge-illuminated > thing. Not that applicable to the small display you're using, but > interesting Always fun pulling stuff apart to see how things are done on an industrial scale

I've done some more tinkering today and think it's as good as it's going to get, and is totally acceptable. This arrangement really suits me because of constraints within the case. A LED can now go under the overhang of the LCD past the end of the driver IC, which was previously unused space http://home.clear.net.nz/pages/joecolquitt/led+lcd.html Had quick play with red LEDs and the new diffuser. Better illumination but still looks odd (every backlight I've ever seen has been yellow/green/blue). May suit the right application

One of the best tips in a while. Thanks! ---------------------------------------------------------------------- Originally posted by Jinx: I've done some more tinkering today and think it's as good as it's going to get, and is totally acceptable. This arrangement really suits me because of constraints within the case. A LED can now go under the overhang of the LCD past the end of the driver IC, which was previously unused space home.clear.net.nz/pages/joecolquitt/led+lcd.html ----------------------------------------------------------------------

Jinx wrote: > I've done some more tinkering today and think it's as good as > it's going to get, and is totally acceptable. This arrangement really > suits me because of constraints within the case. A LED can now > go under the overhang of the LCD past the end of the driver IC, > which was previously unused space > > http://home.clear.net.nz/pages/joecolquitt/led+lcd.html Nice work. > Had quick play with red LEDs and the new diffuser. Better > illumination but still looks odd (every backlight I've ever seen has > been yellow/green/blue). May suit the right application Red would be useful for nighttime applications because doesn't effect the pupils as much. Products for hobby astronomers and other applications where night vision is important all use red displays. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com

Spray painting would make the job go much faster than adhesive foil. But before you spray all 50, do one test piece with a fairly heavy coat of paint. Most (not all) spray paints on the market attack acrylic plastic and make it "craze". Fine hair-line cracks develop - sometimes right away, other times after a few days. MD Jinx wrote: >>Nice work. > > > Thank you. One of the refinements I want to try, as I've 50 of > these to make, is to spray the acrylic with aluminium paint rather > than use foil. If it works it's worth making a mask for that many >

> White paint might be almost as good > (aluminum paint has a lot of variability in how "shiny" it is.) Aluminium/silver paint I tried does coat well but it's rubbish for this. The particle size is too big and didn't produce the mirror I hoped for. I have some 3mm plastic mirror somewhere, would rather use that instead of aluminium paint. White / light colours (or Hot Pink !!!) are best http://home.clear.net.nz/pages/joecolquitt/led+lcd.html OK, I'm done for now. Maybe next week if I'm in the fabricators I'll get some coloured acrylic scraps and try it out

I've made what will probably be my last update http://home.clear.net.nz/pages/joecolquitt/led+lcd.html Using wrapping cellophane (scraps from the local florist), plastic shopping bags, and coloured acrylic offcuts pretty much any tint is possible. I took some time to make a properly painted white diffuser and a well-fitting milled/routed protective sheet. The end result is that light "hotspots" are minimised. Satisfied that I've got the effect I wanted (cheaply) and the jigs to do it

Looks great Jinx! For future reference, you can buy theatrical gel (tinted plastic to change the colour of lights) in diffusions as well. Some major manufacturers are Rosco, Lee Filters, and GAM. The nice thing about using them is that they are smooth and uniform, and also not very thick. Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams On Mon, 03 Jan 2005 00:32:12 +1300, Jinx <joecolquittspam_OUTclear.net.nz> wrote: > I've made what will probably be my last update > > home.clear.net.nz/pages/joecolquitt/led+lcd.html > > Using wrapping cellophane (scraps from the local florist), plastic > shopping bags, and coloured acrylic offcuts pretty much any tint > is possible. I took some time to make a properly painted white > diffuser and a well-fitting milled/routed protective sheet. The end > result is that light "hotspots" are minimised. Satisfied that I've got > the effect I wanted (cheaply) and the jigs to do it

> Looks great Jinx! Reckon.. I know it's just a couple of LEDs and some tinkering but it's a worthwhile product enhancement. The pictures don't convey the depth of colour. Unfortunately I can't afford plane fares for 2000 (maybe 7 but you'll have to bring your own chair, packed lunch and make your own way home) so you'll have to take my word for that > For future reference, you can buy theatrical gel (tinted plastic to change the colour of lights) in diffusions as well. I'll remember that. This time of year there's a lot of colourful plastic packaging around (present and sweet wrapping etc) which was convenient Went out for a leisurely bike ride the other evening to check out dumpsters around factories to see if there was anything else that could be useful. Almost without exception they were padlocked for the holidays. Now how Christmassy is that ? Might just have well stuck a Santa's Helper with a sawn-off on guard. Only scored a rain-soaked VCR, for some reason in a waste paper bin (don't think VCRs have been made of paper since 1973) and a large amount of 1.5mm steel wire (= cheap welding rod) from my mate Engineer Barry's scrap metal pile. "Take whatever you can carry" he always says. Perhaps one day I'll shock him and make off with an I-beam on the handlebars ;-) That'll be the day after the bottle of Super Leg Vitamins arrives

At 03:07 PM 1/2/2005 -0800, you wrote: >On Jan 2, 2005, at 2:10 PM, Jinx wrote: > >>This time of year there's a lot of colourful >>plastic packaging around > >In general, are people finding it useful to use white LEDs and >colored filters rather than pure-color LEDs? > >BillW That wastes a bunch of the light by absorbing it in the filter, but you have a lot more options as to color that way. Want a pink or teal backlight? Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" @spam@speffKILLspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

Possibly my last post about this, but who can tell Previous experiments were tried using the EBT Optronics NSPW-500BS 6400mCd. I couldn't get the price of that below NZ$2.89 @ 100 so looked around. Got some samples of the Ligitek LKW3333 3000mCd (via Hagemeyer) and that works just as well. The difference is scarcely significant, and it's NZ$1.49 To fit the LED under the display (the final board has no sockets) I took 3mm off the LED with a belt sander and made it into a flat- top. For this application it makes no difference to the brightness and in fact the absence of a lens helps spread the light before it hits the diffuser. The LED had been painted white to stop light coming out the side (and probably some will bounce back and come out the top) before sanding -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.298 / Virus Database: 265.6.11 - Release Date: 1/12/2005