Search found 337 matches

by McKlaud
Fri Mar 23, 2018 11:44 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 238
Views: 123585

Re: ZX81 ULA-in-a-CPLD

@Karl: thanks for a hint. :idea: I will go for a dual non-inverting Schmitt-trigger IC like 74LVC2G17 made by Nexperia. These units can source/sink up to 50mA. :geek:
by McKlaud
Fri Mar 23, 2018 6:08 pm
Forum: Hardware
Topic: LCD Output for ZX81
Replies: 6
Views: 4195

Re: LCD Output for ZX81

Hi Rich, I've been using a 4.3" LCD monitor with a composite input, similar to this one: https://images-na.ssl-images-amazon.com/images/I/41k4R0BtMrL.jpg I did a special supply cable, and I use a UK1200 PSU for feeding the Zeddy and the monitor. The monitor fits well on the top of the Zeddy case and...
by McKlaud
Thu Mar 22, 2018 1:26 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 238
Views: 123585

Re: ZX81 ULA-in-a-CPLD

@karl: At the moment I have got two power rails on the PCB, one is +5V directly from the Zeddy board and the second is +3.3V rail for the CPLD. The video output of the CPLD is connected to a transistor buffer. The transistor is fed off the +5V Zeddy rail to avoid any CPLD switching noise on the +3.3...
by McKlaud
Thu Mar 22, 2018 10:06 am
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 238
Views: 123585

Re: ZX81 ULA-in-a-CPLD

In my case I create +3.3V for the CPLD from the Zeddy +5V rail using LM11117-3.3V plus 4 capacitors (100nF & low ESR 10uF) at both sides (in & out). However, for video output buffers I've decided to go for +5V which is noisy. So, it is time to change and don't use +5V rail from the Zeddy board for a...
by McKlaud
Thu Mar 22, 2018 9:10 am
Forum: Welcome Area
Topic: amateus
Replies: 6
Views: 3817

Re: amateus

Hi António
by McKlaud
Thu Mar 22, 2018 12:16 am
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 238
Views: 123585

Re: ZX81 ULA-in-a-CPLD

Hi Andy, Looks interesting. I'd added and tested the ferrite bread + caps (0.1uF and 10uF) in similar fashion as you shown above, but it didn't help much in my case. I think the issue is with the noise coming to the ULA PCB from the Zeddy mainboard. It seems that the +5V and GND are the carriers. So...
by McKlaud
Wed Mar 21, 2018 11:10 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 238
Views: 123585

Re: ZX81 ULA-in-a-CPLD

Very, very interesting discussion, I am reading and learning a dark magic of Zeddy from both of you. :geek: Thanks a lot gents.
by McKlaud
Mon Mar 19, 2018 11:27 pm
Forum: Hardware
Topic: ZX81 Letters
Replies: 15
Views: 8246

Re: ZX81 Letters

I've tried all these enamels with various brushes ... it was a waste of time and money. Yes, indeed, you can match nearly every colour what you can think of but final results are not as good as you expect. Using the oil based marker makes your works easy and stress free with painting just the top of...
by McKlaud
Mon Mar 19, 2018 11:11 pm
Forum: Hardware
Topic: ZX81 Letters
Replies: 15
Views: 8246

Re: ZX81 Letters

You can use an oil based marker with a fine tip. I used this method on raised letters on Zeddy's case when I did a refub last time. Red is not as deep as the Sinclair one but looks good.

Image
by McKlaud
Mon Mar 19, 2018 10:57 pm
Forum: Development
Topic: do we still use UHF modulators ?
Replies: 17
Views: 7958

Re: do we still use UHF modulators ?

PokeMon wrote: Mon Mar 19, 2018 10:48 pm I have two new modulators here just for the case or maybe I got a collector over the time. 8-) :mrgreen:
:mrgreen: if you did wait another 37years, yes definitely it would be worth a fortune in "Antique Roadshow" :mrgreen: