Thread: Zx81
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Old 11th Mar 2020, 8:29 pm   #44
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 8,879
Default Re: Zx81

In theory you could do it in the same way as on the Spectrum, by disconnecting the input and output wires from the modulator inside the housing and wiring the video-in signal straight through to the centre pin of the UHF-out terminal.

The only problem with that is that it directly exposes the output of the ULA (an exotic, expensive IC) to the outside world. It might be better to build a simple buffer circuit to go between the ULA and the outside world into the modulator housing, as in this article:-

https://www.classic-computers.org.nz...o-for-zx81.htm

That shows the basic circuit and general principle of a buffered composite video modification, although I would hope you would try to make yours look neater than the end product in that article.
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