7-seg LED display teardown - Page 1
Forum section: electronics / projects

author: josuah
author_rank: Regular Contributor
timestamp: November 27, 2022, 06:28:10 pm
content: Out of curiosity, as a follow-up tohttps://www.eevblog.com/forum/projects/low-cost-character-display-solution/I cracked one of these inexpensive 7-seg display to understand what they were.They do not open, they just break and the layer do not come apart, sorry for the salvage methods.it looks like rather than using LEDs, itisan LED.It looks very similar to how a single THT/SMD LEDs would be made:(m1): looks like the same material as the LED "glass", that easily cracks but extremely sturdy at that thickness!(m2): I suppose some dielectric material, active part of the LED, which looks like made out of fibers... FR4?(m3): I suppose the conductor part of the LEDs... Which kind of looks like silicon (as in wafers).(m4): no idea why there would be some burried layer like that... There is nothing here. Same as (m6).(m5): some opaque cache make out of plastic-looking material, softer than (m1).(m6): the diffuser glass but more translucent. Goes quite deep, might be why these parts are so thick.(m7): thin layer of plastic-like black material.

author: james_s
author_rank: Super Contributor
timestamp: November 27, 2022, 09:10:03 pm
content: There's nothing too mysterious about how these are made, they're built much like ICs with the LED dies bonded to a metal framework that forms the leads. Then a molded housing forming the segments is placed over that and the inside is filled with translucent epoxy of the same sort used to make ordinary indicator LEDs.

author: josuah
author_rank: Regular Contributor
timestamp: November 27, 2022, 09:35:01 pm
content: Thank you for confirming this.I thought (and so did someone else I sent this image to) that it would have tiny LEDs, a small PCB, and plastic case and a diffuser on top.

author: mariush
author_rank: Super Contributor
timestamp: November 27, 2022, 09:49:53 pm
content: Here's a teardown which shows how tiny the leds are :https://www.flickr.com/photos/queck/1791476380/in/photostream/here's an ancient soviet era seven segment display (incandescent bulbs) :https://hackaday.com/2018/11/06/soviet-era-7-segment-display-built-like-a-tank/I remember seeing under microscope one of those read / bubble hp seven segment displays but can't find pictures or youtube video now.A bit sideways but Posy on Youtube has a 3 video series about LCD displays (in watches)... lots of designs are showed very close up, and explains how lcd works, so I think it's worth checking out

author: josuah
author_rank: Regular Contributor
timestamp: November 27, 2022, 10:00:06 pm
content: Quote from: mariush on November 27, 2022, 09:49:53 pmGreat! Now we have proper work rather than my savage "whack it all" approach.

author: josuah
author_rank: Regular Contributor
timestamp: November 27, 2022, 10:05:50 pm
content: Quote from: mariush on November 27, 2022, 09:49:53 pmAlthough, this is not the same fabric as the one I have here. The photo says:Quote

author: josuah
author_rank: Regular Contributor
timestamp: November 27, 2022, 11:27:28 pm
content: Quote from: mariush on November 27, 2022, 09:49:53 pmThese were good! And to quote him for something that applies to this whole topic as well:Quote

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2022, 02:50:17 am
content: A lot of cheap LED alarm clocks dispense with the potted displays. They just have bare LED dies bonded to a PCB with a plastic molded piece set on the PCB and a diffuser sticker over the top.

author: josuah
author_rank: Regular Contributor
timestamp: November 28, 2022, 03:25:26 am
content: Quote from: james_s on November 28, 2022, 02:50:17 amPlain dies for the LED, I assume MCU as well, directly on a PCB, building-up the LED display. The result should be quite sturdy with the molded substrate on top.I assume these kind of methods are used all the way to reachthese absurd prices.

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2022, 03:40:29 am
content: Quote from: josuah on November 28, 2022, 03:25:26 amMostly DIP ICs and through-hole parts in the clocks I saw, but they were from the 70s-80s and not quite high volume enough to use COB for the IC. It can certainly be done that way though.That clock you linked to is almost certainly LCD with an LED to backlight it.