Re-purposing a photo frame. Looking to identify the LCD - Page 1
Forum section: electronics / projects

author: viperidae
author_rank: Frequent Contributor
timestamp: July 05, 2015, 12:35:54 am
content: I've got an old 7" LCD photo frame from ~2008Thinking about attaching it to a raspberry pi, however I need to find a data sheet on the LCD panelHaven't had much luck goolging the various numbers or the company website,www.b001.cnI don't speak Chinese but none of their LCM products have a 26 pin option."E203460" is apparently a type of LCD, but I can't find any with 26 pin flatflex'sI'm thinking it's a custom flat flex with a cut down interface size, like a standard 24bit LCD with only 18 bits used.

author: marshallh
author_rank: Unknown
timestamp: July 05, 2015, 04:03:18 am
content: Could also have the RGB channels time interleaved.Wire up a fpga/logic analyzer and watch while it runs.

author: bktemp
author_rank: Super Contributor
timestamp: July 05, 2015, 04:15:04 am
content: More likely: It is an analogue TFT. They are widely used in photo frames, because they are cheap.When you look at the display while it is running: Do you notice 30Hz line flicker?If it is an analogue TFT, then it is quite difficult to drive, because you need so supply several analogue voltages including the image data gamma corrected and inverted every second line.

author: ale500
author_rank: Frequent Contributor
timestamp: July 05, 2015, 04:20:36 am
content: And the RGB signals are sometimes also DC-Biased... ugly... get a /" from EBay with Digital interface, less problemsIf you really want to drive that display, and you haven't found a datasheet,then the driving board, if you still have it, is what you have to analyze.With patience and an oscilloscope capture every waveform for every pin.Some pins will have higher than 5 V voltages, maybe even all differentdriving voltages (no charge pumps in the TFT itself).Little story: I had a photo frame, something like 5" with a 480x243 TFT.It had an analog interface. There where 3 pixel clocks, those were 3sinusoids with a few MHz, three biased color signals and various bias,sync, and some other alternating signals.The display had RGB analog input but these signals had alternating polarity,if I remember correctly. The display is as dumb as it gets, there is no drivingthere at all just a DAC, so you have to provide all this information yourself.From the German forum mikrocontrollernet, you can get a (maybe similar who knows)pin out of a 7" with 26 pins interface analog TFT:Quote

author: poot36
author_rank: Frequent Contributor
timestamp: July 05, 2015, 05:46:52 am
content: I would start by traceing the tracks from the display connector to what ever chip they connect to on the main board. You may be able to use the ADC or DAC on the photo frames original main board and just send the right signals to the chip instead of trying to directly drive the lcd. My 3 experiences with this sort of thing 1. portable dvd player lcd had a 5 bit digital input on the lcd itself and used a decoder chip that could take analog composite or s-video or be switched to digital 8bit bt656 data as an input. 2. wireless car backup camera lcd unit lcd took digital bt656 data from a composite to bt656 converter chip made by analog devices. 3. old 2003 hp digital camera i think used analog of some format to the lcd but did have a analog devices drive chip that could take analog rgb and send it to the display as well as to a composite video out jack.

author: amyk
author_rank: Super Contributor
timestamp: July 05, 2015, 01:01:13 pm
content: E203460 is the UL listing number, not the part number. Notice the UL logo ("RU") next to it.It looks like there are plenty of 26-pin LCDs with the same pinout, and they're all analogue.http://www.hiehachi.narod.ru/http://www.beyondinfinite.com/lcd/Library/Hannstar/HSD070I651-C.pdfhttp://www.distrib-informatique.com/lcd/Library/Pvi/PW062XS3_V1.2.pdfAssociated timing controller:http://www.icbank.com/icbank_data/semi_qna/ups015.pdfThe thought occurred to me that an analogue input LCD would be ideal for interfacing to VGA if it was the right resolution, since the signal path could be made all analogue from the video card's DAC to the LC driving electrodes. No converting back to digital and then to analogue again with reduced resolution, hence 18bpp/21bpp/24bpp panels etc.There is a 26-pin digital pinout, but it's for smaller (240x320) modules - probably not applicable to yours:http://datasheets.gpio.dk/dl/ST22TM28%20V02.pdf

author: funkathustra
author_rank: Regular Contributor
timestamp: July 06, 2015, 06:44:10 am
content: Eww, not worth it.Just buy a new 7" LCD from China. I go throughBuyDisplay.comquite often and have never had problems with their product quality.You'll end up with a display that actually has a datasheet, a standard pin-out, and that uses standard parallel RGB signals to drive it.

author: viperidae
author_rank: Frequent Contributor
timestamp: July 20, 2015, 04:16:48 am
content: Thanks guys.Looks like it's probably analog. Not worth it.

author: miguelvp
author_rank: Super Contributor
timestamp: July 20, 2015, 04:23:36 am
content: Build yourself a simple R2R DAC, or use it as an 8 color display. Just because is analog you don't have to use the intermediate values.Edit: for example, most TE displays don't seem to use more than the 8 color combinations from RGBWith a simple 2 levels per RGB component with a simple R2R DAC you could easily do 16 colors:

author: bktemp
author_rank: Super Contributor
timestamp: July 20, 2015, 05:00:54 am
content: Quote from: miguelvp on July 20, 2015, 04:23:36 amIt is not enough, because the LCD needs an AC signal. So you need at least 3 levels (a lower voltage for on, a middle voltage for off and a higher voltage for on. High and low levels are alternated each line). You could do that after the dac using inverting opamps + muxes, but it is not worth it. It ends up with a board full of analogue power supplies, amplifiers and drivers. Using a digital tft all that stuff is already integrated. And the image quality of an analogue tft is not as good as digital ones in most cases.

author: amyk
author_rank: Super Contributor
timestamp: July 20, 2015, 05:11:15 am
content: If anything, it is an excuse to practice your mixed-signal design skills...