Thread: Zx81
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Old 13th Mar 2020, 9:57 pm   #48
John Earland
Hexode
 
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
Default Re: Zx81

Quote:
Originally Posted by SiriusHardware View Post
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.
Iíve just noticed in the first picture in this article, showing the set up, the cassette recorder is the one I have, a Sony!

Iíve read this article and it involves using a resistor and a transistor. I have a 100R resistor and Iíve ordered a transistor so will attempt the mod. However, I did this on the Spectrum without using either of these. Would this approach work here do you think?
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