Ridiculous TV board venture FAIL

A project log for Ridiculous [LCD] Display Hacks

What more can I say?

Eric HertzEric Hertz 11/05/2015 at 04:320 Comments

Spent several days' efforts on adding my TV-board to one of my old 15in monitors...

Long-story short (actually wrote a long lead-up, but didn't post it yet). NEW: It's Posted:

Long-story short, ended up installing it in (more like *on*) the one that has a dual-pixel LVDS display (as opposed to the other, which has parallel-RGB-input).

The TV-board outputs single-pixel LVDS, so I made use of my single-to-dual converter... Finally another use! And (once I found one that didn't have a pin ripped out of the TQFP) it worked right off the bat, AWESOME.

So, that was the first day or so...

Then, I don't know how many days it's been since, but I mounted the board, rewired all the power, got it all closed up. It's not *completely* finished; there's still the buttons and the IR-detector which need to be mounted somehow... (Well, and something about speakers... but that's another venture). But, basically it's darn-near finished... and all that hardware-hacking was a bit of an ordeal. (Oh, I blew out a mosfet I added to switch the power to the display by rewiring the display's power backwards WHOOPS, but the failure certainly could've been much worse, blowing the display rather'n a mosfet!)

So after days of hardware hacking was finally near completion I plugged it in, thought I'd kick back and veg out in front of it for a while, let my accomplishments soak in...

And noticing some strange brightly-colored pixels in the menus. What's that?


I had this connected to an old single-pixel laptop display, previously... same resolution, so basically the only non-cosmetic changes are mounting-hardware and some connectors.

And.... Yeah...

I fought this bright-pixel issue on that display, too... and I didn't exactly *forget*, because when I planned to use the *other* monitor (the one with parallel RGB), I actually considered this "ohhh-yeah" factor in initial design-contemplations...

So what is this "ohhh yeah..." factor?

Well, the TV-board apparently outputs the bits in a different order than the de-facto FPD-Link bit-ordering...

The de-facto FPD-Link/LVDS standard has the first three LVDS channels dedicated to the 6 (highest) bits of each color. That accounts for 18bits per pixel, which is pretty common. A fourth (and possibly fifth?) channel can be added that usually carries two lower bits for each color. That way, if you connect an 18bpp display to a source that outputs 24bpp, all you have to do is leave the fourth channel unwired. The lower two bits, then, are just ignored... same as val_6bit=val_8bit*64/256 (in integer-math). Pretty smart, really. And they make connectors with that in mind.

However, FPD-Link, as I recall, doesn't exactly *define* the actual bit-ordering for the colors, it's more of a suggestion.

And, here, it seems, the TV-board outputs it differently... I haven't actually broken out the signals to determine for certain, but my old experiments had me turning the "brightness" (not the brightness of the backlight, but the brightness of the RGB-data) down to some small percentage. Having done-so, the image from most video sources looked fine. However, the menus always apparently displayed at the normal brightness, which resulted in gradients that suddenly jump from, e.g. black to dark-blue, then suddenly jumping to bright-blue. Looks *awesome* in anti-aliased fonts (i.e. completely unreadable)! And then, when there's a gradient that's not a single color it's even weirder, e.g. black to dark-gray-blue and suddenly jumping to bright red, or something.

Anyways, it looks awful.

The "brightness" fix worked pretty well for video-sources, but the contrast has to be just-right, as well. And even then there'd be an odd "bright" pixel where it should've been dark, and low-contrast... And then there's the On-Screen-Display stuff, like the volume adjustment indicator, and stuff that were barely readable. It was a cludge, and barely usable at the time of the old display; in fact I used the Composite output on the TV-board to feed into my regular CRT TV and used the attached LCD only for navigating menus (as they aren't displayed on the composite output).

So, the failure, I guess, is a weird one... I knew this was a problem, I even considered it in early planning of this project... Not sure why I even went with the dual-pixel LVDS display and my adapter, rather'n making a different adapter for the parallel-display (where I could've rewired the bits, appropriately). Nevermind the fact that display has speakers built-in. Dumb. And all that friggin' time modifying the housing, rewiring all the power-circuitry, and plenty more... and still no speakers anyhow! But for whatever reason that's the path I took, and spent *days* at it, thinking I was only a few minor steps from totally-complete, before the fail I'd already predicted and somehow forgotten made its appearance.

And now... I dunno, it'd be a bit of effort just to get that display functioning like it used to (VGA input); have to resolder some wires I cut, and a few other things. Also a little bit of work to get the single-to-dual adapter back to functional for its old use... (Oh, and, apparently the Tuner aspect is a lot weaker than I remembered, as in non-functional, WTF? That's what I used it for with the last display. Heck, before the old LCD was added, I'd used it as a digital-tuner for my CRT long enough to have memorized the menus I couldn't see... Weird.)

Suffice to say, it's all been shelved for a while. Three previously-useful/functional systems now basically unusable in their current franken-state.

Realistically, it shoulda been installed in (on) the other display from the start, what's a TV without speakers?