ZX81 monitor

Discussions about Sinclair ZX80 and ZX81 Hardware
r00t
Posts: 14
Joined: Sat Sep 03, 2016 7:43 am

ZX81 monitor

Post by r00t » Sat Sep 03, 2016 7:54 am

Hello ZX81 warriors.

I just got a couple of ZX81's in US (I am assuming VHF signal), but unfortunately I don't have the usual monitor solutions to test them (no old TV, no VCR, no composite convertors, etc).

I am wondering if any of these little hardware may enable my laptop to display the ZX81 tv signal:

1)
http://www.ebay.com/itm/252368317239

2)
http://www.ebay.com/itm/201403380615

thanks!

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1024MAK
Posts: 1826
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 monitor

Post by 1024MAK » Sat Sep 03, 2016 11:24 am

Hello and welcome :D

If the computer can do VHF, there should be a channel switch on it.

Item 1) is no good.
Item 2) is a maybe / long shot. The listing does not say that the device can receive analogue TV.

You need a device that can receive an analogue TV signal. The second problem, is that the first ZX81s were designed to work with black and white / monochrome televisions. ZX81s work well with these sets.

But it's not so simple with colour TVs. They produce a poor contrast, very dark picture on some colour receivers. This was fixed when Sinclair changed the ULA chip to a later revision. This later chip includes the "back porch" waveform in the video signal.

If you can solder, there are modules available from time to time (two different modules from two different sellers, one of which is away at the moment) on www.sellmyretro.com that can allow a ZX81 or TS1000 to produce a cleaned up bright clear monochrome composite video signal that is acceptable to colour receivers. It is then much easier to find a converter so that you can use a VGA monitor/display.

The two modules are:
‬ZX8-CCB (developed from the ZX81-CCP).

ZXVid

Note that I don't sell either of these.
Please ask if you would like more information.

Mark

r00t
Posts: 14
Joined: Sat Sep 03, 2016 7:43 am

Re: ZX81 monitor

Post by r00t » Sat Sep 03, 2016 7:56 pm

Thanks!

And how about this one?

3)
http://www.ebay.com/itm/HDTV-HD-LCD-Ana ... 2030392108

Maybe it is a good try for 18.50 including free shipping.

I've checked the ZXVid and the main drawbacks are the price and that you need to solder. I prefer for the moment a non-intrusive technique.

Greets.

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-B-
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Joined: Wed Jul 16, 2014 11:12 am

Re: ZX81 monitor

Post by -B- » Sat Sep 03, 2016 8:19 pm

There is also the Chroma interface which gives RGB video via a SCART socket.
You could easily make a breakout cable, I don'y think SCART/Peritel is seen often in the US.

http://www.fruitcake.plus.com/Sinclair/ ... erface.htm

-B-

r00t
Posts: 14
Joined: Sat Sep 03, 2016 7:43 am

Re: ZX81 monitor

Post by r00t » Sat Sep 03, 2016 9:27 pm

I don't get the point why is so difficult to convert VHF/UHF to composite, I remember back in the VCR era most has VHF/UHF input and composite output, I am right?

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gammaray
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Location: Texas

Re: ZX81 monitor

Post by gammaray » Sat Sep 03, 2016 9:43 pm

Without knowing what computer you have, you probably could use this:

http://www.ebay.com/itm/Coax-Cable-TV-T ... SwrklVMBXz

Also this for the RCA cable to convert one end to coax:

http://www.ebay.com/itm/Eagle-F-Male-to ... xyBvZTV-4U

Any comments?

[edits made]
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

gozzo
Posts: 444
Joined: Fri Jul 08, 2011 7:52 pm

Re: ZX81 monitor

Post by gozzo » Sun Sep 04, 2016 1:52 am

it is certainly not easy to convert vhf/uhf rf tv to composite - directly, it has to pass through a tuner to convert it to an if of around 39mhz, usually, then amplified and gain-controlled, demodulated, and then amplified again to get to standard video level....i've been trying to find a cheapo/easy way for ages, such as feeding the rf into a almost biassed off transistor(to act as demodulator) but no luck, not enough input amplitude...and amplifying uhf is not easy!

gozzo
Posts: 444
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Re: ZX81 monitor

Post by gozzo » Sun Sep 04, 2016 1:53 am

vhf is a bit easier than uhf , so 'might' be more possible to do a cheapie....

r00t
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Joined: Sat Sep 03, 2016 7:43 am

Re: ZX81 monitor

Post by r00t » Sun Sep 04, 2016 2:50 am

@gozzo:

Have you tried any of the hardware I mention?

The one that gammaray points also looks very promising.

@1024MAK:

Do you have any further comments on the hardware that gammaray points?

Greets.

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX81 monitor

Post by 1024MAK » Sun Sep 04, 2016 9:07 am

gammaray wrote:Without knowing what computer you have, you probably could use this:

http://www.ebay.com/itm/Coax-Cable-TV-T ... SwrklVMBXz

Also this for the RCA cable to convert one end to coax:

http://www.ebay.com/itm/Eagle-F-Male-to ... xyBvZTV-4U

Any comments?

[edits made]
The tuner/converter linked to above at least sounds like it should work.
You will also need a good quality screened coax phono/RCA to phono/RCA lead (look for one described as a video lead, not a cheaper audio lead).

Mark

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