Monitor mode compatible overscan

[jfm75]

Hi all,

First post

by dilwyn » Thu Mar 06, 2014 9:55 am
This is a short message which was sent to me recently by John Moody, via my blog, on the subject of the upscaler devices. I hope someone finds it useful

Hi Dilwyn,
Reference the above on the QL forum:-
Scart pin 16 is a switch for RGB/Composite, RGB= 1 to 5 volts
I connected a germanium diode + to pin 16 and orange wire (PAL) from the QL. This selects the RGB input. works with the HDMI unit from City Skys....

Seems I needn't have bothered to post this

[vanpeebles]

Hello

[dilwyn]

Hi all,

First post

by dilwyn » Thu Mar 06, 2014 9:55 am
This is a short message which was sent to me recently by John Moody, via my blog, on the subject of the upscaler devices. I hope someone finds it useful

Hi Dilwyn,
Reference the above on the QL forum:-
Scart pin 16 is a switch for RGB/Composite, RGB= 1 to 5 volts
I connected a germanium diode + to pin 16 and orange wire (PAL) from the QL. This selects the RGB input. works with the HDMI unit from City Skys....

Seems I needn't have bothered to post this

Oops, sorry John, didn't mean to steal your first post...

[jfm75]

@Dilwyn

That's not a problem, it wasn't what I meant

Just that I posted via your blog to try and get reference to scart pin 16 here asap!

But it appeared to be ignored in the following post!

[ppe]

Many thanks for the advice. I feel a foolish for not reading all of the earlier material through more carefully.

@jfm75 can you please explain how the germanium diode solution works? I guess I just don't know enough about electronics to understand how the PAL signal through a germanium diode supplies >1V to the pin If I had to guess I'd venture it has something to do with rectifying the PAL video signal resulting in an average voltage of >1V ?

Kind regards,
Petri

[1024MAK]

Try it without the diode first

Simply put, the signal level of a composite signal is sometimes just enough to fool the SCART switching circuitry in the receiver. Very handy if the retro computer does not have any "proper" SCART switching signals available.

Alas, germanium diodes are rather hard to get hold of these days. But yes, the diode will only conduct in one direction. but at the expense of a slight voltage drop across the diode.

What the actual result is depends as much on the output circuit of the QL and the input circuit of the receiver as the diode. The PAL composite signal (from pin 3 of the video/monitor socket) is a positive voltage video signal that comes from the PAL video encoder chip.

Mark

[ppe]

It does work perfectly with composite PAL connected directly to pin 16. I guess the SCART input on the device luckily is not too picky about the input signal!

Now I have a perfect setup for my monitor and was able to ditch the old jammaboards converter, what a great hobby success for the weekend!

Thank you so much Dilwyn, John, Tobias and Mark (I hope I didn't forget somebody) for your time and effort in helping me out. Hopefully this thread will help others as well!

Cheers,
Petri

[dilwyn]

Many thanks for the advice. I feel a foolish for not reading all of the earlier material through more carefully.

@jfm75 can you please explain how the germanium diode solution works? I guess I just don't know enough about electronics to understand how the PAL signal through a germanium diode supplies >1V to the pin If I had to guess I'd venture it has something to do with rectifying the PAL video signal resulting in an average voltage of >1V ?

Kind regards,
Petri

I think a germanium diode was used in preference to a silicon one as it has a lower voltage drop. However, as members have found, it seems to work without the diode too.

[jfm75]

@jfm75 can you please explain how the germanium diode solution works? I guess I just don't know enough about electronics to understand how the PAL signal through a germanium diode supplies >1V to the pin If I had to guess I'd venture it has something to do with rectifying the PAL video signal resulting in an average voltage of >1V ?

The original idea was based on a recollection from years ago (probably a faulty one!) pass a variable voltage through a diode (Yes Dilwyn, voltage drop 0.2v) with a capacitor. The capacitor would assume peak voltage, providing the current drawn was low enough.

The fact was, in my case, it worked with just the diode so I left it in hoping it would give a certain level of protection to the QL circuitry.

In any event it was the pin 16 thing I was trying to put across. I had tried over the years to get RGB Scart from QL to TV to work without success until I got the City Skys unit and it didn’t work either. Until pin 16 RGB/Composite switch came to light.

John

[jimre]

Hi All!

Finally I have found an equivalent of the upscaler sold on eBay (unfortunately only in U.K.) and tested by Dylwin:
http://dilwyn2.wordpress.com/2014/02/16 ... -displays/

That is generally available in many EU countries, as it is sold by Conrad under order no. 989271:
"SpeaKa Professional SCART and HDMI/HDMI converter"
http://www.conrad.com/ce/en/product/989 ... no-Adapter

I bought it today afternoon. It works well with my QL (RGB-SCART cable) and Samsung LCD TV/Monitor (HDMI). I can feed the VGA input of my monitor using a HP HDMI->VGA converter connected to it's output.

I have put some pictures of the different screen modes here:
http://gigant.chem.elte.hu/ZXSpectrum/Q ... converter/

The best modes were the 720p and 1080p when using the RGB input. The 800x600 mode was blurred, the 1024x768 was a little bit better and so on... I got the worst picture quality using the AV composite input from the SCART cable. (This unit uses the standard SCART BLANKING signal for composite<->RGB selection.) Of course the HDMI->VGA conversion decreased the picture quality and the picture was blurred as for the 800x600 mode.