TFT LCD for Raspberry PI B - Page 1
Forum section: electronics / general

author: SilentAce
author_rank: Newbie
timestamp: February 09, 2015, 01:38:36 pm
content: Hi Members,First post here. I need some help regarding a TFT LCD. My plan is (if it works at all) to use it as my primary monitor for my raspberry pi server, since it's small and doesn't take much space. I also have the documentation for the LCD which would be of great help, but the problem is i don't really understand it. I know that it uses a 24pin flat cable. So i have tons of questions, here we go:1. I guess the most important question is will it work with the Raspberry Pi? The input for the LCD is VR, VG, VB so i am guessing it's RGB analogue signal?2. Does it work with RGB or it works with HSYIO(horizontal) and VSYIO(vertical) signal as well? Or do i need to use both?3. What are the most important pins to make it work?4. What are the voltage requirements? The logical power supply is rated at 6V, but there is also a power supply for the gate driver which is about 17V? I guess i need both?5. What is the voltage requirement for the lamp? I know i need an inverter to get it working.Well if we make this work it would be so awesome, if not it's not much of a loss because i got the LCD for 1$.The photos and documentation are in the attachments.

author: legacy
author_rank: Super Contributor
timestamp: February 09, 2015, 01:41:38 pm
content: that LCD needs a controller, it is not directly compatible with any of the PI video signals.

author: Prime73
author_rank: Regular Contributor
timestamp: February 09, 2015, 01:44:35 pm
content: You need to build/buy a controller for the LCD. Ben Heck had an episode on driving an LCD using FPGA you can check it out to get you started. In general I would just buy a $20 LCD already with controller and GPIO header compatible with RPi and call it a day.

author: bktemp
author_rank: Super Contributor
timestamp: February 09, 2015, 01:58:24 pm
content: This TFT display needs analogue input signals. It is designed for PAL/NTSC video, but it needs a lot of analogue processing (composite -> RGB, RGB -> gamma correction/inversion). It is simply not worth it spending a lot of time and money to drive this old display. There are highly integrated ics for driving those type of tft lcds, but they are hard to get and it is even harder to get the datasheets. Buying a new, digital tft will give much better performance for the same money.

author: miguelvp
author_rank: Super Contributor
timestamp: February 10, 2015, 06:42:56 am
content: Quote from: bktemp on February 09, 2015, 01:58:24 pmNot sure where are you getting that from, I only see an LVDS connector meaning differential pairs for 4 lines and 2 channels for higher resolution screens for a total of 8 differential pairs + ground + VCC, there is also EDID and other things to take into consideration that talks to the panel on the fist differential pair. One of the differential pairs is dedicated for the clock as well.Minimum connection would be 4 differential pairs, two ground cables and two VCC (probably 3.3V) and of course you have to turn on the back light via the other connector (red and yellow) And for that you need a high voltage driver most likely.The Pi, can't drive that display directly since it has a DSI display connector for LCDs. Also it's only accessible via the GPU it seems and you are stuck to the displays that the Broadcom driver supports, so getting a DSI to LVDS might be a worthless pursuit.But you can find HDMI/DVI to LVDS controllers, but you need a controller that will drive your LCD.For example this was a weekend project to make myself a display for my dev boards with an LCD that can display up to 1920x1200 at 60HzMy wife bought some wine at Costco, and she was going to trow away this fine box (Made in China of course):So I measured the inner size and fitted a laptop 15" display capable of up to WUXGA (1920x1200)I did carve the two slots where the display will tuck in, and used industrial velcro and some left over pieces of wood to hold the screen in place, mounted the controller board and control panel and wired it all up including the CFL high voltage driver, all powered with a 12V 4Amp brick.Powered it up and this is how it looks from behind.And the front (the case cover is there just for the fun of it, I'm going to cut the plexiglass so I can close the back but leaves the connectors exposed.This is running out of a Pi B via an HDMI to DVI adaptor (so no audio) but the controller has an audio input and I could hook an amplifier and add speakers in the future (I sure have the space in there)Detail of the display at full resolutionAll the parts (display, controller, CFL, power brick) came from ebay and I don't recall who I bought them from since it was a long time ago.The previous housing for the display was a pizza box (here it is showing Android ICS running on a TrimSlice, the small, well tiny, computer on the right of the desk with the green led on).So I guess I upgraded from a pizza box to a wine box display

author: bktemp
author_rank: Super Contributor
timestamp: February 10, 2015, 07:36:58 am
content: Quote from: miguelvp on February 10, 2015, 06:42:56 amFrom the datasheet. Where did you see a LVDS connector?

author: miguelvp
author_rank: Super Contributor
timestamp: February 10, 2015, 07:47:30 am
content: Missed the pdf all together and that looked like an LVDS connector, my badOnly thing to do with that display would be to use the composite output and convert it to RGB+Composite Sync and it will look awful.bktemp is right, looks like not a good solution plus the native resolution (400x234) is bad to begin with.

author: bktemp
author_rank: Super Contributor
timestamp: February 10, 2015, 08:47:26 am
content: It is not only the analogue signal: The analogue signals are probably going directly into the lcd glass. Therefore you need to apply gamma correction and inversion of the voltages every line to the signals. In the 1990th and early 2000th when those displays were widely used for cheap tvs or video camera screens, ics for that purpose were available (like TA8696F).Those ics convert the RGB signals into appropriate signals for driving the lcd screen, but the image quality will still be far from what is considered good by modern standards.If you really want (and have a bit of background knowledge of how a tft glass works), you can build your own driving circuit, but as I said, it is not worth it spending much time or money.In the last years cheap tft modules with integrated HMDI, VGA and composite inputs became available from china.If you just need a small video display, 3.5" 320x240 with composite input is a good choice. 800x480 and 1024x600 are other common resolutions. They cost around 20-100$ depending on size and input options. I have one with hdmi input and 1024x600 resolution connected to a raspberry pi. It it the easiest and cheapest way to get a small tft panel connected.

author: SilentAce
author_rank: Newbie
timestamp: February 11, 2015, 11:56:33 am
content: Thank you all for the replies. I know 400x234 is not the most visually appealing resolution for the hd standards we have today. Time-wise it would be best to get a 7" screen with all the electronics off ebay. It was worth a try, and as i said it's not much of a loss. There is one use for the display now to be recycled and shaped into something else.@miguelvp that is some cool use for that wine box.All the best.

author: Rasz
author_rank: Super Contributor
timestamp: February 11, 2015, 07:04:17 pm
content: Quote from: miguelvp on February 10, 2015, 07:47:30 amCompositeyou Americans are so funny with your backward ways, composite and mpeg2Rest of the world had RGB (and Svideo) outputs/inputs on everything while you were stuck with shitty composite.as for this screen, SilentAce you can play with VGA output from your computer. You will need to either manually program VGA CRTC, or use something like powerstrip to define exact timings required by that module, you should be able to use RGB and sync signals directlycontrary to popular belief VGA CRTC is very nimble and can be coerced to some extremely non standard timings. My first PC had VGA ISA card connected to a PAL TV using Scart port (direct RGB) and small DOS TSR program enforcing PAL compatible timings). Text modes, games (Doom) worked like a charm.you can pretty much forget about this lcd working with peeedit: there is VGA666 board for pee that lets you output VGA, but pee doesnt let you directly program CRTC, only pick one of predefined video modes, so that also wont workon the other hand it turns out pee has a real parallel RGB HVsync LVTTL interface and IS capable of driving LCD screens directly (as long as they are ok with default timings)