50Hz or 60Hz?

Discussions about Sinclair ZX80 and ZX81 Hardware
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mikeh_nz
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50Hz or 60Hz?

Post by mikeh_nz »

mrtinb wrote: Fri Jan 20, 2023 2:14 pm
I have place a jumper in series with the R30 resistor on my board, so I can change between NTSC and PAL. Some games works better in one of the positions.
New to the forums so can’t PM yet. But possibly this will be of interest to others…

Do you have any pictures of how you did this?

I’m in the states & I’m wondering
  • which games work better with more scan lines?
  • Are there some that work better with USA 60 Hz?
  • Should I leave my zx81 without R30 and at UK 50Hz. That is, is it better to have more resolution with scan lines and instead use a solution like rgb2hdmi with an analog front end to render the screen in hdmi?
  • If I leave it at UK 50Hz, can I get it to display on my USA Tv?
Thoughts?

Cheers
Mike
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mrtinb
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Re: 50Hz or 60Hz?

Post by mrtinb »

The resistors are a little tight on my board, so I have added a little shrink tube at the bottom of each leg, and the R30 resistor to one end. So if I short the jumper on the top, I get NTSC, and if it’s not shorted, I get PAL.

(It’s not really NTSC/PAL, because there is no color. It’s 50/60 Hz)

Some games made for the Brazilian clones run too fast in “PAL” mode and becomes unplayable.

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1024MAK
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Re: 50Hz or 60Hz?

Post by 1024MAK »

mikeh_nz wrote: Sun Feb 05, 2023 4:05 am
  • Should I leave my zx81 without R30 and at UK 50Hz. That is, is it better to have more resolution with scan lines and instead use a solution like rgb2hdmi with an analog front end to render the screen in hdmi?
Only you can decide. Obviously the vast majority of ZX81s in Europe run their video at 50Hz. Hence most games are designed for this. That does not always mean that they will not work okay on 60Hz video. It’s not something that I’ve tried much.

As I have TVs that work with my ZX81, I’ve never actually tried using a composite (or RGB) to HDMI converter with one. Note that if using a RGB type, all three channels plus the sync input need to be connected together. That may be enough to get it to work. Otherwise the sync signal needs separating from the composite video from the ZX81.

I did once try a very cheap composite to HDMI converter with another computer, but the quality was poor.
mikeh_nz wrote: Sun Feb 05, 2023 4:05 am
  • If I leave it at UK 50Hz, can I get it to display on my USA Tv?
Ahh, that depends. Are you feeling lucky?

In Europe, a lot of modern (as in LCD) TVs use chips and circuitry that is actually multi-standard compatible, hence can display a 525 line 50Hz NTSC video picture.

But as the U.S.A. is such a big market all on its own, it’s worthwhile producing TVs that are only compatible with the video standards in the U.S.A.

However, despite this, it has been found that some will actually display a 625 line 50Hz picture without problems, even though there is no mention of this in the specification, instructions or manual.

There will also likely be some where the capability to display a 625 line 50Hz picture was included in the specification, instructions or manual.

Hence, the only way to know, if it’s not already stated, is to try. You cannot harm a LCD display by feeding it a ‘wrong’ video standard signal. And the original reason for the vertical frequency being the same as the mains frequency is no longer relevant.

Also, if you want, you could use a switch. You only need a simple SPST type.

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mrtinb
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Re: 50Hz or 60Hz?

Post by mrtinb »

mikeh_nz wrote: Sun Feb 05, 2023 4:05 am That is, is it better to have more resolution with scan lines and instead use a solution like rgb2hdmi with an analog front end to render the screen in hdmi?
My experience is that most composite-to-hdmi adapters are useless. This is because the signal from a ZX81/TS1000 is not close to the standard. Hence the picture becomes garbled, or unstable with new tv hardware.

I have bought an old B/W surveillance monitor, as I could not get a stable picture with anything else.

So my advise is to buy the oldest B/W tv you can find.
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mikeh_nz
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Re: 50Hz or 60Hz?

Post by mikeh_nz »

Thanks for all the info.

You should check out the rgb 2 hdmi project - it was built for the bbc micro, but can do a lot of other retro computers. I have it on my beeb and it’s super sharp.

I would expect it would end up very sharp and clear as you put it into zx81 mode & its sounds like it’s taking its input straight from pin 16 of the ula (plus a 220 ohm resistor in between). It does not need the back porch to work.

https://github.com/hoglet67/RGBtoHDMI/wiki

Sample screen grabs (including a zx81 one)
https://github.com/hoglet67/RGBtoHDMI/ ... Screencaps
desiv
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Re: 50Hz or 60Hz?

Post by desiv »

If you aren't using RF or aren't planning to, you can use the "no longer needed" channel switch to choose between 50hz or 60hz.
It's described on the Tynemouth post about the TS1000...
http://blog.tynemouthsoftware.co.uk/201 ... o-mod.html

I did that with my TS1000 and it works great.

I am using a Commodore monitor and it works fine (tho I do have to play with the vertical hold sometimes to get it to stick).
Haven't tried it on a newer display...
mikeh_nz
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Re: 50Hz or 60Hz?

Post by mikeh_nz »

Nice!
Spinnetti
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Re: 50Hz or 60Hz?

Post by Spinnetti »

I'm in the US and have pretty much all the Sinclair models. Just do the composite mod which you'll want to do anyway to get a decent picture. Most screens auto adjust to whatever you feed it. I just used a $20 converter off Amazon to convert from Composite to VGA and use an old VGA monitor as I much prefer the 4:3 format as was used back in the day, and smaller screens instead of a monster 16:9 tv of today.
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