Friday, 4 August 2017

Minstrel ZX80 Clone V2.5 boards

I have updated the design of the Minstrel ZX80 clone slightly, the new boards are V2.5.
The main change is the addition of a block of jumpers under the ROM socket.
These give the option of using an original ZX81 24 pin ROM chip instead of the 28 pin EPROMs normally used. These jumpers are pre-wired for 28 pin mode.
If you want to use a 24 pin ROM, you need to cut the traces which set 28 pin mode.
Once the links to 28 pin mode are cut, fit wire links for 24 pin mode,
Then just build the rest of the board as normal, other than fitting a 24 pin socket.
This means if you are using a ZX81 donor case, you can also use the Z80 and ROM chips from the original board (if they are working), along with the heatsink if you want to use a linear 7805 regulator.
As before the boards are available in blue and green.
The blue goes well with the RC2014 keyboard
The green is the more classic look.
The other jumpers on the board are also pre-wired, so you can build a version without needing to fit any jumpers or make any links.
You can fit jumpers where you want to change an option, just remember to cut the track underneath first.
For example here on the ROM selection jumpers, the board is wired for all three selections set to high. This will select the highest 8K image in your EPROM. Defaulting to high allows the use of EPROMs from 27C64 to 27C512. On the smaller capacity chips, the pins are unconnected or are only required for programming and for normal operation should be pulled high.
I have also revised the keyboard overlays. These are keyboard overlay which can be stuck over a ZX81 membrane (or more likely a ZX81 replacement menbrane).
The first is for use with the original ZX80 4K integer BASIC, and uses the keywords and colour scheme of the ZX80.
The second is for use the with ZX81 style 8K floating point BASIC. This has a different set of keywords and symbols and also follows the ZX80 colour scheme.
This shows the ZX80 style 4K version on the left, and the ZX81 (which uses the 8K BASIC) on the right, and in the middle is the new intermediate ZX80 8K BASIC hybrid. I have moved the top row of keywords above the top row of keys, as the ZX80 does. Thanks again to Grant Searle who provided the base artwork for the two original keyboards.
These were intended for use with the Minstrel to make a ZX80 clone for a ZX81 case.
Or with a ZX81 membrane on a base of some kind, I use a clear sheet of perspex on the open frame versions I sell on Tindie.
Here the membrane connectors are mounted on the underside of the board.
However, you can also use them to customise your ZX81 - like this one built by @zx_priestess.
Also in this batch of overlays, I have produced a TS1000 overlay.
The layout is almost identical to the ZX81, but has 'delete' instead of 'rubout' and 'enter' in place of 'newline'. These can be used if you need to replace the membrane on a TS1000, you can fit a ZX81 membrane then this overlay on top.
You could also use these on a normal ZX81 if you prefer DELETE to RUBOUT etc.
The Minstrel boards, overlays, kits and built units are available from my Tindie store.

You can also order PCBs and / or overlays below. Price includes postage.
Minstrel ZX80 Clone Issue 2
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