Adding CCFL light or LED backlight to a 6 digit/7 segment LCD display - Page 1
Forum section: electronics / projects

author: hafrse
author_rank: Regular Contributor
timestamp: January 12, 2020, 02:16:29 pm
content: Hello,Is possible to add CCFL light or LED backlight to a 6 digit/7 segment LCD display which has no backligt from the beginning? I have seen some article about doing that many years ago (could not find now...) by removing the reflective shield layer from the backside , not sure if I should seprate that shield from a possible layer (polirization ?) between it and the LCD glas or other consideration that I should be aware off.ATtached 2 images from the LCD displayMnay thanks in advance!.

author: SeanB
author_rank: Super Contributor
timestamp: January 12, 2020, 06:49:54 pm
content: How about adding side illumination to the edges of the display instead. Not as even, but will work well enough for most applications, using only 2 thin SMD led chips per side. You can get the chips new, as modules you place next to the display, or grab them off an old flat screen LED backlit display easy enough, though often those are a multichip module per pack, often having around 9V forward drop, but really bright at 20mA. done that a few times to a LCD display to make it night readable, not even, but better than nothing, and pretty much the common method for these displays.

author: james_s
author_rank: Super Contributor
timestamp: January 12, 2020, 06:54:40 pm
content: It really depends on the display and whether there's room. Also it's difficult to get a nice smooth illumination, EL strip does work well though if you have space and power budget for the inverter.

author: Buriedcode
author_rank: Super Contributor
timestamp: January 15, 2020, 03:11:17 pm
content: You would probably have to remove the reflective coating on the back, which isn't easy as it'll be bonded well. Then you could use an off-the-shelf backlight panel (light pipe) for character LCD's. Example:https://shop.pimoroni.com/products/white-led-backlight-module?variant=36999548170https://www.aliexpress.com/w/wholesale-led-backlight-panel.htmlI believe the polarizer is layers are on the front of the display, but there could be one on the back.The downside of converting a reflective display to one with a backlight is, the contrast takes a hit when the backlight isn't on. Many displays are "transflective" which is a combination of the two - a partially reflective coating that allows some light through for the backlight. Your display *might* have that, but it is easily checked - if it lets any light through the back. EL strips are great if you have limited space (<2mm) but a hassle to drive when compared to a single LED lightpipe.

author: james_s
author_rank: Super Contributor
timestamp: January 15, 2020, 08:43:53 pm
content: On many displays the reflective coating is just a sticker that peels off easily, I helped a friend add a backlight to some GameBoys a while back. I suppose it could vary widely though.

author: splin
author_rank: Frequent Contributor
timestamp: January 16, 2020, 07:50:08 pm
content: Here's one reasonably successful attempt:https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.youtube.com/watch%3Fv%3DoEu7nqOkKxo&ved=2ahUKEwj2sdCr8YjnAhVWUhUIHfYkDlcQwqsBMAF6BAgLEAg&usg=AOvVaw2pJHcJS28Fv3xmTJiO7zD2&cshid=1579204112123It wasn't perfect but does show some of the pitfalls.

author: james_s
author_rank: Super Contributor
timestamp: February 03, 2020, 07:40:28 pm
content: That should look way better than that one in the video.My vote would be EL strip. It can be cut to size and produces a nice soft even glow. The only concern I'd have is that the inverter that powers it could possibly interfere with the low AC ranges. EL can also be powered directly from the 50/60Hz AC line but it won't be as bright.

author: james_s
author_rank: Super Contributor
timestamp: February 03, 2020, 11:16:52 pm
content: That's an interesting part, I considered going with LED when I replaced the EL backlight in one of my scanners but I couldn't find anything suitable off the shelf at the time. EL looks nice but scanners are typically left on all day and the backlights wear out.

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2020, 07:48:51 pm
content: Yes that will be fine, LEDs are current driven, just add an appropriate resistor to burn up the excess voltage, adjust the value to get the brightness you want while staying under the max rated current.

author: rdl
author_rank: Super Contributor
timestamp: February 14, 2020, 05:19:49 pm
content: That turned out really nice. Good job.About how thick is that backlight?

author: james_s
author_rank: Super Contributor
timestamp: February 17, 2020, 05:25:03 am
content: That really does look good, looks like it was made like that.