Retrofit LCD display light - any tips?

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Can't figure out what you're talking about. You have such a light and want to figure out what you can do withit????

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Take a look at the Philips scopes LCD display backlight, the lamp is in the "L" shape perspex running the length of the display (lower images)

Basically a piece of Perspex to the rear of the display with a milled out lamp hole, internal reflection lights the display from the rear. maybe do the trick? The gap behind these displays is however quite large, 3-4mm so you may not have sufficient thickness.

JC

I'm not sure that you are going to have too much success with this. I have tried before to light displays that were not intended for it, and have never managed to get enough light in there to make it work. On transreflective types, the reflective surface is, I seem to recall, bonded to the back face of the glass panel, to maximise the light reflection back through the panel, and minimise the losses. The light output from high intensity white LEDs is also pretty narrow angled, so you might struggle to get even illumination across the display surface, if you attempt to side inject it. How about a couple of the surface mount LED 'bars' that you can get now, perhaps fixed along the two long edges of the display, casting their light across its surface. I'm sure that with a bit of imagination, they could be shrouded and fixed on in a way that looked ok. Can't remember where I saw them now, but I'm sure that one of the newsletters that I get from suppliers, or a mag advert somewhere, showed some bars that were 'snap-off' to the length / number of LEDs that you needed. Googling might turn up something along those lines.

Arfa

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The problem here is the LCD backing plastic has some legends and segment marking on it, associated with reading the LCD, and is not translucent enough to pass much light through. So having to pass light into the glass of the LCD. Have painted the inside of the well in the plastic outer casing, that receives the LCD panel, with white correction fluid to reflect back some of the light from 2 bright white LEDs mounted at one edge and angled diagonally. Not ideal but gives just about adequate illumination.

But I can launch the LED light straight to the LCD glass edge, unlike your scope example where the light has to go round the bend. I will try a photo, under this LED light, when completed.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

You *could* add an EL backlight replacing the backing sheet. The following link may be usefull if you dont have any scrap EL backlight LCDs to cannabalize.

They have a A5 size blue green cut to size EL sheet for $26. You could get 8 2" square (+ contacts on one end) pieces out of that.

RS have a suitable product as well.

Seikosha White electro-luminescent sheet 60x50mm (you can trim it to size)

You'd also need an inverter (backlight driver) for either product

12V 45ma supply. 5V model also available, less than 1" cube.

HTH.

Ian.

I've done this quite a lot in the past. There are a few things to note though.

The sheet on its own is useless, there is no way to atatch the wires, as it is plastic. (except maybe conductive epoxy which I'm sure I tried years ago without success) What you need is the kit, which contains terminal strips and the all important conductive glue pads to attatch them to the sheet. Farnell sells this.

The back of the sheet is one of the conductors, so this should be insulated. I use electrical tape. Hot lamination machines destroy the sheet. There are cold laminators available.

You cut the sheet to size using scissors, though I have read that if you don't seal the edges, the sheet can start to fail round the edges as moisture gets in. (unsubstantiated claim). I fold the elctrical tape over them.

Sometimes after all your efforts they do not work, as the two terminals become shorted. This could happen during the cutting with scissors operation, I don't know, I just stat again.

The sheets are very expensive - make a careful note of the sizes and how many backlights you can make out of them - some sizes wll provide only a couple of strips and a lot of wasted sheet due to their dimensions and the way the borders are made. Much more economical to get the larger sheets.

I did have one occasion where the display would not accept the backlight at all - the original was LED, and I assume the invertor drive (around 100v a.c) interfered with the electronics.

You can get these pre-made on Ebay. That might actualy be your best option given the above.

Gareth.

I haven't tried this but there is also a product called EL wire or "Glow-Wire". It is a flexible plastic fluorescent tubing, powered with an inverter in the same way as EL sheet. RS and Farnell stock this stuff but at a massively inflated price compared with what you can get it for from the club / entertainment industry. (Google Glow Wire) Seems to be very cheap in bulk from the States.

You might be able to run some of this under or around the display, but you'll still need an invertor.

Gareth.

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My camera does not work well enough at low light levels to produce an image worth capturing. But visibly works well enough with, 2 off, using 25mA white

5mm LEDs angled diagonally. The white tippex on the other side works quite well, in reflecting back some, for filling in the opposite side of the LCD.

Not the sort of kit that justifies electroluminescent panels and inverters etc, just a get by solution was fine. A "Saltire" illumination pattern was acceptable here.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on