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RGB on 48K

orangeorange
edited December 2008 in Hardware
Is it possible to get better picture (RGB, or at least composite video) from ZX 48K without opening it? (using the expansion port only)
I think there was a signal called 'video' on that port. BTW, why is it so hard to find a pinout for that port? It isn't even mentioned here: pinouts
Post edited by orange on

Comments

  • zxbrunozxbruno
    edited November 2008
    Take a look at this page:

    http://members.tripod.com/~piters/uvyrgb.htm

    If you really don't want to open the Spectrum, that's the way to go. An example of an old interface that did that was this one:

    ftp://ftp.worldofspectrum.org/pub/sinclair/hardware-pics/FergusonMA20RGBInterface.jpg

    The output was via a din-connector, which isn't the best thing nowadays. I sent mine to Spain for a friend to take a look at it and see how it works.

    The new K-Mouse Turbo interface also takes advantage of the same pins, but gives you an RCA-style video output jack:

    http://velesoft.speccy.cz/kmturbo-cz.htm
  • GodsGods
    edited November 2008
    ALL ZX 48k who was sold in France got one RGB (Peritel) converter to connect to the TV set. Look at EBAY (France).
  • orangeorange
    edited November 2008
    ebay france doesn't have many spectrum hardware, unfortunately.. or I didn't search enough..

    What would happen if someone simply connected UVY signals on expansion port together, could that be composite?
  • WinstonWinston
    edited November 2008
    orange wrote: »
    BTW, why is it so hard to find a pinout for that port? It isn't even mentioned here: pinouts

    I found it _somewhere_ because I put it in the Spectranet schematics. There is a PNG of a work-in-progress Spectranet schematic here which shows the edge connector pinout on the left of the diagram:

    http://spectrum.alioth.net/doc/images/c/c7/Spectranet-wip1.png

    Edit. Damn, on second thoughts that shows a +3 edge connector and omits the video signals.
    Still, the Orange Book has the 48K's edge connector in it.
  • ZupZup
    edited November 2008
    You may get composite video with a 10 ohm resistor, connecting it to the video signal on the expansion port. At least, that states Microhobby, on issue 32 (pages 22, 23, 24 and 25).

    I haven't tried that, but making an internal interface is very easy (look at this schematic, from Swedish DIY site)... and it works fine.

    In that page, you can find a SVHS interface (easy to do, but I haven't tried). I guess that choosing SHVS or composite video is a matter of tastes, when you're daling with 1 mm or 1.5 mm pixels.

    RGB is more difficult. And I doubt that you may get better quality. RGB modes are great when you start with RGB data... but in Spectrum RGB to YUV conversion are made inside ULA, so you only get YUV data and lose quality when converting YUV to RGB again.
    I was there, too
    An' you know what they said?
    Well, some of it was true!
  • GodsGods
    edited November 2008
    orange wrote: »
    ebay france doesn't have many spectrum hardware, unfortunately.. or I didn't search enough..
    Look here... ebay.fr
  • WombleWomble
    edited November 2008
    Beware if you find a Fergusson MA20 RGB interface for the speccy, it does not take its power from the expansion slot. The DIN socket on the Fergusson TV not only accepted the RGB signals inbound, but it provided the 12V output on the central pin, so try to use it without the right TV and it gets now power, and consequently doesnt do anything. It puzzled me for a while as when the speccy was powered up obviously all the edge connector lines lit up on the MA20 PCB. I ended up finding the schematic for the original TV which showed the 12DC output. I had to rig up a very weird cable with a power jack on the side of the 9pin D Sub my RGB monitor takes. Gives an utterly cracking picture tho, images so sharp you can almost shave with it.

    Hah - there is actually one on ebay.co.uk right now - have told the seller about the problem.

    http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=360109251463&_trksid=p2759.l1259

    If you are not averse to making up a weird cable you can get this going. Am happy to help anyone who buys this - like l say - awesome picture.

    Thats mine set up.

    http://i40.photobucket.com/albums/e230/Womble76/specsetup.jpg

    Me trying to work out what the feck was going on with it initially (HDD to give the ATX PSU some load while it was on but disconnected)

    http://i40.photobucket.com/albums/e230/Womble76/rbgspec.jpg

    The solution..

    http://i40.photobucket.com/albums/e230/Womble76/fruity_cable.jpg
  • piterspiters
    edited December 2008
    Zup wrote: »
    In that page, you can find a SVHS interface (easy to do, but I haven't tried). I guess that choosing SHVS or composite video is a matter of tastes, when you're daling with 1 mm or 1.5 mm pixels.

    RGB is more difficult. And I doubt that you may get better quality. RGB modes are great when you start with RGB data... but in Spectrum RGB to YUV conversion are made inside ULA, so you only get YUV data and lose quality when converting YUV to RGB again.

    I made S-VHS, better said S-Video out from Speccy 48K. Pic is more clear than via composite, but there is a big drawback - misalign. Reason is that required PAL delay is made inside ULA, more-less accurate. It compensates in TV PAL decoder. If we attach to S-Video input then no need for delay. Probably I should add some delay line on chroma signal, but was not in mood to bother with all it more...

    RGB-YUV conversion can be done pretty simple and with high quality, as it is only mixing of signals.
    How you know that inside ULA is made RGB-YUV conversion ? Maybe it generates straight YUV :-) I mean, it is totally irrelevant in fact, both use 3 lines for 3 signals.
    Quality loose happens when making some color encoding as PAL or NTSC - because we need to reduce 3 signals on 1 line - it results with less sharpness, interferences between luma signal and chroma (carrier) signals. Reason whay S-Video is better is exactly that - separating mentioned 2 signals.
    My YUV-RGB produces pretty good RGB. Much better than composite.
  • ingoingo
    edited December 2008
    piters wrote: »
    How you know that inside ULA is made RGB-YUV conversion ? Maybe it generates straight YUV :-) I mean, it is totally irrelevant in fact, both use 3 lines for 3 signals.

    ULA does this for simply forming PAL signal using only 2 transistors and one LM1889.

    I also use YUV=>RGB converter from france which gives sharp picture.

    Ingo
  • piterspiters
    edited December 2008
    ingo wrote: »
    ULA does this for simply forming PAL signal using only 2 transistors and one LM1889.
    I also use YUV=>RGB converter from france which gives sharp picture.
    Ingo

    ULA gives out YUV because Sonclair choosed such encoder which requires YUV. It is complete irrelevant for this discussion how many transistors PAL encoder with LM1889 needs. There are PAL encoder chips where no transistors at all needed. Very likely LM1889 was cheapest on the market then. In Spectrum 128 we have RGB from ULA mostly because it has RGB out for CGA monitors.
  • csmithcsmith
    edited December 2008
    piters wrote: »
    ULA gives out YUV because Sonclair choosed such encoder which requires YUV. It is complete irrelevant for this discussion how many transistors PAL encoder with LM1889 needs. There are PAL encoder chips where no transistors at all needed. Very likely LM1889 was cheapest on the market then. In Spectrum 128 we have RGB from ULA mostly because it has RGB out for CGA monitors.
    Incidentally, your standard Speccy uses RGB internally throughout the ULA, and then goes through some nasty phase shifting at the last minute during the analogue output to generate YUV, which is what the telly used internally, and consequently most video encoders at the time converted from YUV.
    So you're probably right piters, that the LM1889 was the cheapest chip.
  • GodsGods
    edited December 2008
    csmith wrote: »
    So you're probably right piters, that the LM1889 was the cheapest chip.
    Back in the year 1983 there was very few PAL encoder chips to choose...
  • ingoingo
    edited December 2008
    piters wrote: »
    Reason whay S-Video is better is exactly that - separating mentioned 2 signals.

    Reason why S-Video is better is (exactly) because the Y signal is not bandwith limited to the color carrier - because of the separate signals. Combination of Y and color signal needs bandwith limitation of Y signal which leads to bad quality of composite signal.

    Ingo.
  • piterspiters
    edited December 2008
    ingo wrote: »
    Reason why S-Video is better is (exactly) because the Y signal is not bandwith limited to the color carrier - because of the separate signals. Combination of Y and color signal needs bandwith limitation of Y signal which leads to bad quality of composite signal.
    Ingo.

    Yes, yes. But as you may see, Speccy 48K has not bandwith limit. filter in PAL encoder. What is a flaw, caused with usual spare, I think.
    I made S-Video mod of Atari STs PAL encoder with MC1377. Chroma filter is removed, together with Y delay line. http://ppera.07x.net/atari/stvid/stvid.php

    So, bandwith limit results with less sharp color parts. But it is something physiology based - as human eye has less sharpness for colors than B/W. Other thing is possible interference if luma and chroma freq. (multiplies) are close. Then, some distorsions may happen in encoders and decoders. Phase shifting is worst - it results in wrong colors.
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