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Author Topic: My old ZX81 restored to full function  (Read 15419 times)
gertk
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« on: October 16, 2011, 08:35:53 PM »

At the Commodore meeting last saturday I found a complete ZX81 set. My own ZX81 was disassembled many many years ago to build it into a (wooden) case with a real keyboard, a monitor and cassettedeck and the case was stored in the attic. The whole system was sold a long time ago and the empty case was forgotten. I found the case back when I moved into this house 10 years ago and stayed on the lookout for a working PCB.

The system I found in Maarssen had a broken keyboard flatcable but that was repaired on the spot with a pair of scissors kindly provided by the kitchen. My own case was almost brand new so I decided to put the board in my own case anyway. It still has the red ZX81 logo.
Now the ZX81 is alive again, the rampack which came with the set is working perfectly also but is a non Sinclair product called:

"SPECIAL RAMPACK by audio computers" and the 'special' part made me open the case. It seems there is room for some more chips but I have not found out yet what they might be, perhaps some rom expansion or such. One big plus for this rampack is that it sits on very tight and there is no sign of the dreaded 'sinclair wobble' which cost me lots of coding hours back then.
  
« Last Edit: May 22, 2012, 07:21:02 AM by gertk » Logged

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gertk
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« Reply #1 on: October 16, 2011, 08:36:37 PM »

The 'special rampack' disected
« Last Edit: May 22, 2012, 07:19:45 AM by gertk » Logged

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Seob
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« Reply #2 on: October 17, 2011, 07:09:00 PM »

Yes the ram pack wobble of death. That was a major design flaw.
Nice to see a piece of history restored.
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« Reply #3 on: May 21, 2012, 02:05:16 PM »

nice one... didn't see this topic before.

i got my zx81 composite modded the other day, because te lack of proper vsync made it near impossible to find the tv channel.
my first zx81 game release should be out soon too
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« Reply #4 on: May 21, 2012, 08:52:27 PM »

i got my zx81 composite modded the other day, because te lack of proper vsync made it near impossible to find the tv channel.
my first zx81 game release should be out soon too
Yes it can be quite a pain to get these oldies tuned on your TV, that is also why I mod every G7400 to have at least RGB and nowadays I also mod them with CVBS.

BTW How is your new ZX81 game distributed ? as WAV, MP3, K7 or on good old cassette ? Smiley
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« Reply #5 on: May 21, 2012, 09:08:19 PM »

good old cassette & wav ;-)

There already is a small free twirldemo from 2010 available for download at www.revival-studios.com , it also includes a WAV, so you can hook it up to the real deal.  My first game "avalanche" (a version of colorclash for the zx81) is finished, so i'll start production of the cassettes soon.


« Last Edit: August 15, 2012, 10:36:41 AM by revivalstudios » Logged

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« Reply #6 on: June 18, 2012, 07:18:55 PM »

Last meeting in Maarssen I found out that the board I put into my ZX81 is a rare Issue3 board.

We did a video mod on an Issue 1 board ZX81 of a friend of mine from which he could not get a decent display on his TV (back porch problem in the older ULA chips)

After replacing the inner contents of his modulator by this small piece of Vero board he could connect it to a standard CVBS input and he's got himself a nice rock solid and clean black and white picture.

 
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« Reply #7 on: August 15, 2012, 10:44:34 AM »

2 games for the ZX81 are now ready for release, with a third game currently in the making.

"Avalanche" (2011)" - A version of colorclash for the ZX81
"Mayhem (2011)" - Yup!

I've also added support for peripherals such as the ZXpand joystick interface and AY soundboards.
The games will be available on cassette tape as well as download.

If you are wondering what these games would look like on a rusty-old 4-chip ZX81? Then come visit me at the Retro gaming fair on september 9 in Deurne, the netherlands!

PS1> I am terrible at electronics so i did the qucik-n-dirty composite fix on the zx81. I get a good picture, except when loading.

PS2> I also built a raspberry-pi into a zx81 case (with the zx81 keyboard working as an actual keyboard). I might bring it for displaying videos/trailers
« Last Edit: August 15, 2012, 11:12:25 AM by revivalstudios » Logged

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« Reply #8 on: August 15, 2012, 06:55:45 PM »


PS2> I also built a raspberry-pi into a zx81 case (with the zx81 keyboard working as an actual keyboard). I might bring it for displaying videos/trailers


Damn I put a spare mbed inside a ZX81 case Smiley But I bet my mbed powered ZX81 beats your raspberry Pi in boot time by far :-)
I did not want to show the pictures yet..

I did this in between projects to get some special mbed routines going.
It features VGA (and optional CVBS) video output, sd card storage (FAT16/32 with LFN), joystick and PS2 keyboard all without active hardware. Speed is about 4 - 5 times original not optimized just plain C.. Oh, and you can also use the original keyboard alongside the PS2 keyboard.

Screen is mapped onto 640x240 VGA B/W output but not yet with Z80 interrupts, most programs and games work, even with UDG but your Twirl demo and some other non-UDG Hires games not yet. The (original) Basic rom thinks it is running on a ZX80 with ZX81 basic rom (always fast mode) but the VGA output is always on (note there is no real VGA output on an mbed... I use the I2S output at 25 MHz bitrate...)
Added features when using a PS2 keyboard: F1 help screen, F2 dis-assembler and F3 hexdumper/editor(not yet). You can reboot with Ctrl-Alt-Del and most of the PS2 keys like : and , . < >  cursor keys etc. are generating the correct ZX81 equivalents.

I am taking this NXP81 :-) to Maarssen this Saturday (Commodore gg)
 
« Last Edit: August 15, 2012, 07:00:49 PM by gertk » Logged

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« Reply #9 on: August 15, 2012, 08:56:35 PM »

Here are some pictures..

Note: the weird horizontal line pattern at the top is coming from the mini LCD TV not from the mbed. (it is a cheap 7" China thingy)
On two other VGA inputs (bigscreen LCD TV and a 17" VGA LCD they are not there)
« Last Edit: August 15, 2012, 09:17:40 PM by gertk » Logged

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« Reply #10 on: August 15, 2012, 09:00:18 PM »

and some more..
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« Reply #11 on: August 15, 2012, 09:55:15 PM »

Really nice gert! Unfortuanately i cant make it to maarsen, but be sure to mention my new and upcoming games to anyone taking interest in ZX81!

I don't have photos of my pi81 atm, but it all fits nicely inside the case with composite and sound out connected, HDMI and ethernet going inwards via cables and a nice USB hub in the cartridgeport.
It all looks nice, but i am not really a linux-expert, so i just did some testing with the debian installation as well as raspbmc.

I have a seperate ZX81 with composite out, zxpand interface (SD card, 32k ram extension) and AY interface (joystick port and AY chip) for development, which i will also bring to Deurne to demonstrate my zx81 work.
The zxpand is supossed to fit a memorex expansion case, but i still need a case to fit both the Zxpand + AY interface

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« Reply #12 on: August 15, 2012, 10:22:00 PM »

Some video footage..  Smiley It shows only a game but about halfway I switch to 'turbo' mode and the action gets really frantic...
In the beginning you can see the sdcard fileselector which uses the full 640x240 resolution.

YouTube: http://www.youtube.com/watch?v=2Q1VQDkFSwI
« Last Edit: August 15, 2012, 10:34:01 PM by gertk » Logged

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« Reply #13 on: August 15, 2012, 10:32:55 PM »

Really nice gert! Unfortuanately i cant make it to maarsen, but be sure to mention my new and upcoming games to anyone taking interest in ZX81!

I will do some advertising. Do you use special graphics stuff (HiRes) in those games or is it DisplayFile with standard characters based ?

Quote
I don't have photos of my pi81 atm, but it all fits nicely inside the case with composite and sound out connected, HDMI and ethernet going inwards via cables and a nice USB hub in the cartridgeport.
It all looks nice, but i am not really a linux-expert, so i just did some testing with the debian installation as well as raspbmc.

I did get my raspberry pi a month ago but only tried some small things, I also have the Debian install on a 4GB sd card and it runs ok just takes forever to boot...

Quote
I have a seperate ZX81 with composite out, zxpand interface (SD card, 32k ram extension) and AY interface (joystick port and AY chip) for development, which i will also bring to Deurne to demonstrate my zx81 work.
The zxpand is supossed to fit a memorex expansion case, but i still need a case to fit both the Zxpand + AY interface

I don't think I'll be going to Deurne but Apeldoorn is on my list. Let us hope they have better 'power supply' than the last time..
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« Reply #14 on: August 24, 2012, 10:25:46 AM »

Really nice gert! Unfortuanately i cant make it to maarsen, but be sure to mention my new and upcoming games to anyone taking interest in ZX81!

I will do some advertising. Do you use special graphics stuff (HiRes) in those games or is it DisplayFile with standard characters based ?
Displayfile based. I want it to run on stock ZX81 and have quick arcade gameplay at proper speeds. I did get some wonderful animation going which i'm really proud of in 4x6 pixels ;-) Cover art for the 2 release games are currently finished and printed and i should be receiving a high-end tapedeck this afternoon which should help produce quality tapes.

Quote

I don't think I'll be going to Deurne but Apeldoorn is on my list. Let us hope they have better 'power supply' than the last time..
Too bad. Deurne is always a good show. I'm currently looking into origanising my own show next year that will span for 2 days with a lots of new homebrew releases (not only by me), sneak previews at upcoming projects. competitions, systems to play and a retro-fair. Dedicated sections for msx, commodore, etc. Your hardware projects would fit in nicely!

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Follow me on twitter (@revival_studios , @bitstormgames) for the latest information about my upcoming proje
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