ZX81CCP video output for ZX81

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
User avatar
stefano
Posts: 336
Joined: Tue Dec 11, 2012 8:24 am
Contact:

Re: ZX81CCP video output for ZX81

Post by stefano » Wed Dec 26, 2012 9:37 pm

Got the board and mounted it this morning.. now (after also cutting away part of the membrane stripes) my TS1000 is fixed !
The ZX80 port is at a good stage, the last problem to solve is to build a keyboard reading function able to leave the display visible, then some new program for the 4K ROM will see the light ;) .

User avatar
PokeMon
Posts: 2138
Joined: Sat Sep 17, 2011 5:48 pm

Re: ZX81CCP video output for ZX81

Post by PokeMon » Sun Feb 03, 2013 7:08 pm

So finally a new release of the ZX81CCP - it's named ZX81CCB with same crystal clear picture quality but "basic" components. So a cheap but good picture version.
The schematics:
ZX81CCB_schema.gif
ZX81CCB_schema.gif (17.04 KiB) Viewed 620 times
The main part is the powerful output driver for a sharp, crispy picture as known before. I used the same LVC technology from Texas Instruments. There is no more DIP switch but possible to choose the inverted picture by setting a sold jumper (J1). The two xor gates wired parallel looks a bit strange but there should be used either one of the two. The 74LVC1G386 is not more expensive but harder to get so I wanted to leave an alternative with a normal 74LVC1G86. On the other hand I have about 50 of these gates by now which can be used from me. ;) Instead of the second AND gate which is used only as a driver there could be also used an OR gate (74LVC1G32).
ZX81CCB_board.png
ZX81CCB_board.png (14.4 KiB) Viewed 620 times
The board is now very small with about 0.75 x 0.75 inches.

I will let produce a series of these boards which should be available in about 6 weeks. The price will be GBP 4.90 completely soldered and tested. If somebody will attend the German ZX Meeting I will take some boards with me. So you could spare shipment. 8-)

User avatar
sirmorris
Posts: 2669
Joined: Thu May 08, 2008 4:45 pm
Location: oxon, uk

Re: ZX81CCP video output for ZX81

Post by sirmorris » Sun Feb 03, 2013 9:05 pm

:o :o :o Brilliant stuff!!
I will have one or two at the meeting!

C

*edit - definitely 2 ;)
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

Baggers
Posts: 65
Joined: Wed Dec 19, 2012 7:49 pm

Re: ZX81CCP video output for ZX81

Post by Baggers » Sun Feb 10, 2013 9:55 am

These are awesome devices :D I recently got a ZX81 ( issue 1 ), but it unfortunately had a really bad RF signal, you could only barely make out that the ZX81 itself was indeed working!
Wired one of these up in seconds, and hey presto, crystal clear display and composite! worked a treat :D

Thanks!

User avatar
stefano
Posts: 336
Joined: Tue Dec 11, 2012 8:24 am
Contact:

Re: ZX81CCP video output for ZX81

Post by stefano » Fri Feb 15, 2013 11:51 am

Yes, I guess I should say thank you to Pokemon too for the invention, it saved my ZX81 from rubbish.. no, I'm joking, could never trash it , even if it was broken !
The CCP circuit is awesome.. is it normal to see it (quite rarely to be honest) flicker while some text is being printed ?

Hope the zx80 inclusion in z88dk will be appreciated, I'm crossing my fingers, can't wait to know if the software trick to keep the picture stable will work on the real hardware.

User avatar
PokeMon
Posts: 2138
Joined: Sat Sep 17, 2011 5:48 pm

Re: ZX81CCP video output for ZX81

Post by PokeMon » Fri Feb 15, 2013 6:50 pm

stefano wrote: The CCP circuit is awesome.. is it normal to see it (quite rarely to be honest) flicker while some text is being printed ?
I know it is not really 100% flickerfree but this doesn't come from the CCP circuit as it just improves the signal delivered from the ULA.
I think this has to do with the key processing but didn't get very deep into it.
I am quite sure that it will flicker with other solutions (simple transistor output/discoupling) same way.

Maybe this effect is not seen via modulator but this is another way of processing incoming RF data.
Modern TV's have many filters in processing modulated video via RF.
Maybe that's the reason for not beein so obviously via RF.

I plan a new module 100% flickerfree with a buffered picture (frame) which would be suitable for ZX80 machines (keep the last picture until new picture is sent).
For now it is in my mind only but will come true with first tests in about 4 weeks. 8-)

User avatar
stefano
Posts: 336
Joined: Tue Dec 11, 2012 8:24 am
Contact:

Re: ZX81CCP video output for ZX81

Post by stefano » Sat Feb 16, 2013 9:45 pm

Well the CCP trick seems already magic to me :)
But I confirm the latest TV models get in trouble when you issue a LOAD command because they prefer to squelch the output when they do not understand the TV signal fully (which does not happen with an older CRT TV set).

User avatar
PokeMon
Posts: 2138
Joined: Sat Sep 17, 2011 5:48 pm

Re: ZX81CCP video output for ZX81

Post by PokeMon » Sat Feb 16, 2013 10:52 pm

Well I developed the ZX81SCP for it - same as ZX81CCP but has an internal standby sync generator which produces a valid sync signal during LOAD command.
This is not working for the save command as there are created additional sync pulses internal from ULA but LOAD is more used than SAVE.

See this posting:
viewtopic.php?f=6&t=840&start=40#p9981

And the Youtube video for having the well known stripes from LOAD on a modern TV (LCD or PLASMA).

http://www.youtube.com/watch?v=TKNu3kavPl0

User avatar
stefano
Posts: 336
Joined: Tue Dec 11, 2012 8:24 am
Contact:

Re: ZX81CCP video output for ZX81

Post by stefano » Tue Feb 19, 2013 1:13 pm

I saw your post but did not understand it fully, thanks for the video, I could compare the different shape of the stripes :)

dr beep
Posts: 1045
Joined: Thu Jun 16, 2011 7:35 am
Location: Boxmeer

Re: ZX81CCP video output for ZX81

Post by dr beep » Thu Feb 28, 2013 8:29 pm

So I was able to fix the ZX81 after the keyboard membrane was broken, but then my very first TV I bought in my childhood gave up with a spectacular bang and a lot of smoke. On any other TV in the house I can't get a clear picture. Is this board the solution to connect with another old aerial TV?

If so, does it need additional soldering? And please can someone test the latest version of Pinball on a real ZX81 since my picture just doesn't get clear on the alternative TV.
viewtopic.php?f=6&t=1078&start=30#p11282

Post Reply

Who is online

Users browsing this forum: Bing [Bot] and 2 guests