OrangePi PC connected to an ancient CRT television through scart: what resolution to use? Is it supported and how to add it?

1st Official Post

    Hello to everyone. :) I own an OPi PC with the latest jernej's LE 11.0 image on it and I'm trying to use it with an ancient CRT tv set through scart connection. I've also added the 50 Ohm resistor between the composite RCA connector signal and shield as adviced here but the 'issue' (not a real issue but something related to my weird setup) is another here: the lowest resolution I can set is indeed 720x480i which is way too much and the image flickers badly.

    If I'm not mistaken, scart connection works at 320x240. Am I right? Should it be the case is such a low resolution supported by LE and my OPi PC and does it leave LE enjoyable or is it just a dumb effort? Should adding such a low resolution make some sense, how to add it to the list of the available choices?

    Thanks in advance to everyone! :)

    I'm still waiting for some better insight on the topic but in the meantime I've made some research by myself. It seems I was right about the resolution which should actually be 320x240 while I've found this thread where the always very helpful chewitt (he has helped me too a lot of times!) gives an advice which involves using xrandr. Currrently I don't have the OPi PC at hand and I've tried on a Wetek Play 2 still on LE but the xrandr command isn't available there. Maybe it is on the OPi PC: I need to get hold of it and try. I would report any further update. A nice day to everyone! :)

    • Official Post

    In LE the xrandr command is only present on devices running Xorg/X11 windowing (Generic x86_64 devices) but ARM SoC devices "run on the framebuffer" with no windowing system. Other distros, e.g. Armbian are desktop focussed and will use X11. The nearest equivalent is forcing kernel DRM output modes, which can be done via boot params in extlinux.conf.

    I don't have experience with SCART devices, but the standard resolution I've seen with RCA outputs (single cable) in the past is 480p/i and it's cousin the Component output (three cables) is the same but can also run at 720p and 1080p/i. Current Kodi skins are designed for a minimum 720p screen resolution but most (not all, but most) will handle 480p if needed, but lower than that I'd expect to see visual problems as none of the skin designers will be testing low resolutions. Similarly.. I doubt any of our maintainers are testing RCA/Composite output so YMMV.

    Thanks as always! I need to apologize because I've made a mess due to ignorance... NUC (Next Unit of Computing) means something which is Intel based so COMPLETELY different hardware as you point out correctly. Also, I should have known that xrandr is linked with the x11 graphical environment... Completely out of context, completely!

    I've made some more research (I hope smarter than before) and found something which seems more promising here, more or less all the posts by fmafma in particular. What I plan to do is remounting /flash as rewritable then editing extlinux.conf adding something like

    Code
    video=composite-1:640x480@60D

    to the APPEND line BUT I don't know where and how to find the right reference to composite output.

    fmafma was working with HDMI so I don't know the right let's say sintax to add a well formed kernel parameter.

    I've searched a lot for a command to list all the available video outputs, to no avail unfortunately.

    For example, I've found a very well laid down Wiki here and in the end Amlogic devices are discussed but I don't know if it applies to Allwinner ones too. I need to check but I don't think so: maybe still something relevant inside /sys/class but certainly not the same directory structure nor filenames given that they show a clear reference to the Company name...

    I agree my mileage may vary and I could just stop here but I'd like if this wouldn't be the case...

    Edited 3 times, last by -=guybrush=- (August 30, 2021 at 5:06 PM).

    • Official Post
    Code
    WP2:~ # modetest | grep connected
31    0    connected    composite-1        0x0        2    32
34    33    connected    HDMI-A-1           1600x900        27    33

    ^ from an Amlogic device .. "composite-1" is present. Allwinner also uses the kernel DRM framework so something similar should output. The Amlogic section in the wiki is not relevant (old kernels).

    Here I am. I've finally managed to make the necessary changes and check the results... I've checked by modetest and the output is actually composite-1 so here follow my steps:

    Code
    mount -o remount,rw /flash
vi /flash/extlinux/extlinux.conf

    then, I've added at the end of the APPEND line

    Code
    video=composite-1:640x480@60D

    saved and rebooted. No matter what resolution I input there, no changes at all. Obviously, the television still flickers badly. I don't know what to think...

    I've also tried to add the colon between 60 and D in spite of the fact that fmafma says that with kernels newer than 4.15 (and I'm on 5.10.47 so it is absolutely the case) it isn't needed anymore, to no avail unfortunately.

    I've also tried to check dmesg output for "video", nothing relevant apart from the fact it correctly evaluates the added kernel parameter. It doesn't throw any kind of error nor warning (though I expected that being the sintax with the added colon wrong).

    I don't know. All the, let's say, edid stuff isn't present because also fmafma is working on a NUC so a completely different platform but all the rest made sense and I don't know what I'm missing but it doesn't work.

    Hi and thanks for your follow-up! :) Nice to be here talking with you again. Yes, I've enabled composite output by provided overlay, helped by you that time too. It works fine but the only available resolutions are 720x576i and 720x480i and with the both of them the output on that old tv flickers like hell, I assume because the resolution (or maybe just the refresh rate or the both of them) is too high both for the tv and (I believe) the scart connection too. To be honest, recalling that DVD players once hadn't HDMI but just scart connections and a typical DVD resolution is indeed 720x576, then a scart should be capable of handling that but maybe my thought is completely wrong...

    That's the reason why I've tried to lower the resolution following the advices given by fmafma in his thread (though I know it doesn't fit very well my scenario).

    If nothing can be done (and I completely understand losing time on that isn't worth the effort for you nor anyone else apart from me), I'd just like to know if my approach with adding that kernel parameter and how I've done it is completely wrong or not. Thanks as always and have a nice day! :)

    • Official Post

    Composite TV out literally supports only PAL and NTSC modes (720x576i and 720x480i, respectively). No amount of tricks on your part will change that, sorry.

    I find it surprising that your TV wouldn't support at least of one of those modes. They are few decades old standards. I tested this on some camera display from ebay and it worked fine, but it has normal RCA connector, without any resistors in between. I can probably get RCA to SCART adapter, but no promises when.

    I mark the thread as solved. No more to say. Maybe it's the cable but the quality is really poor as it can be easily seen by the photo I've attached. I don't know the reason. I have even tried with a different cable without the added resistor with the same exact outcome.