Re-using 7" tft lcd screen from old dvd player - Page 1
Forum section: electronics / projects

author: skematic
author_rank: Newbie
timestamp: December 13, 2018, 12:49:08 pm
content: Recently I've got a hold of an old but working portable dvd player LG DP450. I intend to use the lcd screen as a display for raspberry pi.What I found inside is a 7" LG lb070w02 tft lcd screen (datasheet). From what I understand fromthe schematics in the service manual, the main mcu MT1389L (datasheet) is driving this LCD directly, and sadly this chip doesn't have a video-in pin.I've looked on google for driver boards for this lcd, however there seems to be none available. I'm really interested making this LCD work, but not sure what to do next. I hope someone can help me out.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: December 13, 2018, 01:30:50 pm
content: What you do next is you bring it to the e-waste center and buy thishttps://www.ebay.ca/itm/5-inch-HDMI-Touch-Screen-TFT-LCD-Panel-Module-Shield-800X480-For-Raspberry-Pi/311872272215?hash=item489d093757:g:S7cAAOSw2ENW63YF:rk:3:pf:0

author: skematic
author_rank: Newbie
timestamp: December 13, 2018, 03:21:26 pm
content: Quote from: In Vacuo Veritas on December 13, 2018, 01:30:50 pmThat'd be an easy (and expensive) way out, however I think it would be an interesting project to get this LCD working (or die trying). I'd imagine I need at least another driver IC for this LCD to convert RPi's composite video signal. Do these exist for this particular lcd's interface? Or should I try to write my own driver with say a STM32F103C8T6?

author: cdev
author_rank: Super Contributor
timestamp: December 13, 2018, 03:27:30 pm
content: I don't know if the newer Pis still support a composite video out (320x240 ish) like some of the lower res displays still use.But the older Pis do. Its very hard to read smaller text on them so you will likely be limited to maybe 40 characters, but if you can live with that its okay.Even cheaper TFT displays that use SPI or i2c are out there for just a few dollars which would be sharper and cheaper.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: December 13, 2018, 03:59:52 pm
content: Well, you could fool around until Halley's Comet shows up again... or just get a screen that works.

author: tsman
author_rank: Frequent Contributor
timestamp: December 13, 2018, 04:31:42 pm
content: Quote from: skematic on December 13, 2018, 12:49:08 pmThe interface on that LCD isn't compatible with the Raspberry Pi at all so you won't be just wiring it up to the expansion header using the DPI peripheral. You're going to be spending far more money and time in designing + making an interface board than just buying a premade working LCD. You'll need to make or buy a compatible CCFL backlight inverter as well. If this is a learning exercise then go for it but be aware it won't be easy.Quote from: cdev on December 13, 2018, 03:27:30 pmYeah. They all support composite video output still but the newer ones have the composite output in the 3.5mm TRRS headphone socket. The Zero boards have it on an unpopulated .1" header.

author: james_s
author_rank: Super Contributor
timestamp: December 13, 2018, 05:03:57 pm
content: It is fairly trivial to drive a display like that with an FPGA, but getting it to work on a RPi is not. These generally have a digital RGB/dotclock interface and require continuous scanning like a CRT. The SPI displays on the other hand have an onboard framebuffer.

author: metrologist
author_rank: Super Contributor
timestamp: December 13, 2018, 05:20:37 pm
content: Can someone recommend an inexpensive and decent Pi display in ~5" size?I too have surplus LCD displays that might be usable, but I don't know what to look for. One is a nice 10" instrument display that I'd like to use for anything I could it to work with - maybe a new thread...

author: tsman
author_rank: Frequent Contributor
timestamp: December 13, 2018, 05:31:36 pm
content: Quote from: james_s on December 13, 2018, 05:03:57 pmOP's LCD takes 3 analogue signals for RGB along with a ton of extra sync signals so even with a FPGA it'll be a hassle for something that is only 480x234 resolution.

author: cdev
author_rank: Super Contributor
timestamp: December 13, 2018, 05:33:17 pm
content: It depends on whether you want to display text, and if so, how? (Typically x characters by x columns)vector graphics and if so, monochrome or color, and also the speed you need. Also, whether you need input capability, i.e. a 'touch screen' and even there there are multiple kinds, some can input multiple spots at the same time (multitouch) and I think some may even be able to gather a bit more info as to whats there, for example, I don't know how it is done exactly but some displays can even register thetiltof a stylus.For the PI's onboard 3D acceleration chip to work you may be limited to using the "display connector" or HDMI.

author: james_s
author_rank: Super Contributor
timestamp: December 13, 2018, 06:36:58 pm
content: Wow I just read the datasheet, you're right, it does have analog RGB inputs. How bizarre, I've never seen a LCD panel that is driven that way. Almost always they are digital RGB, higher resolution panels have a LVDS interface but many smaller or older ones are just TTL.

author: cdev
author_rank: Super Contributor
timestamp: December 13, 2018, 06:48:30 pm
content: I think the Pi's output is composite RGB. Maybe each color could be separated?Its a real shame that monitors, especially ones with touch input, that use the Pi's full display capabilities still tend to be pretty expensive. More than the Pi itself, thats for sure.

author: james_s
author_rank: Super Contributor
timestamp: December 13, 2018, 07:49:54 pm
content: The composite output is just that, composite baseband video. It can be separated into RGB snit that is a far from optimal approach. Those little backup camera monitors are about 20 bucks and accept composite video. The Pi has HDMI and there is also a DSI interface but it's quite hart to find panels that work with the older DSI interface it has.

author: nick_d
author_rank: Regular Contributor
timestamp: December 13, 2018, 11:09:54 pm
content: Another way to do it might be using a mini ITX PC motherboard or smaller if such a thing exists... with something like a Celeron J3455 soldered to the board the price is about the same as an RPI but you must add DDR3 RAM. Get one with a VGA output and you will have the R, G, B analogue outputs and separated sync to drive this LCD.We use an STM32F767 with built in parallel LCD controller that uses about 30 pins to drive inexpensIve LCDs from Ebay. Better LCDs can be had from Digikey, but with cheap commodity models available on Ebay for around $15-20 as used in millions of elevators, fridges and such worldwide, I feel that going the surplus route is not warranted here. A bigger hassle is getting the connector from Digikey for the inevitable flat cable, and surface mount soldering it. Breakout kits from places like SparkFun may help here.cheers, Nick

author: amyk
author_rank: Super Contributor
timestamp: December 14, 2018, 01:03:20 am
content: Quote from: In Vacuo Veritas on December 13, 2018, 03:59:52 pmNo one learns anything by just buying premade stuff.This is not a difficult exercise, if you want to get a timing controller just search "analog LCD controller" and you'll find plenty. Example:https://www.analog.com/en/products/audio-video/display-driver-electronics/analog-lcd-display-drivers.htmlBut the datasheet has all the needed waveforms already.

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: December 14, 2018, 07:53:04 pm
content: Quote from: amyk on December 14, 2018, 01:03:20 amThen why is he buying a premade Raspberyy Pi? At some point, you have to accept you can't build everything with your bare hands from the dirt in your backyard, and that there is an infinity of things you *could* design yourself.