Search found 337 matches
- 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. I will go for a dual non-inverting Schmitt-trigger IC like 74LVC2G17 made by Nexperia. These units can source/sink up to 50mA.
- 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...
- 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...
- 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...
- Thu Mar 22, 2018 9:10 am
- Forum: Welcome Area
- Topic: amateus
- Replies: 6
- Views: 3817
Re: amateus
Hi António
- 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...
- 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. Thanks a lot gents.
- 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...
- 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.
- Mon Mar 19, 2018 10:57 pm
- Forum: Development
- Topic: do we still use UHF modulators ?
- Replies: 17
- Views: 7958