I started on my new ZX-81 replacement board (kit) ZX81+38

[fusebit]

The ZX-81+38 in operation

I have a revision 1.4 which is patched to revision 1.6.

[mahjongg]

Nice!

[fordp2002]

Hi mahjongg,

I have not been following the ZX81 Scene for a while. I remember seeing your older SMT design but I like this new one a lot more.
I would like to build on your project to make a new sister project that is going in a different direction.
It would be great if you could publish the Kicad files.
In return, if my project ever gets off the ground I will send you a PCB free of charge!

[mikeyp]

I've been looking at your schematics and I'm a little confused. Aren't these meant to be 74LS00? 74LS32 is a Quad 2-input OR gate.

74LS32.png (6.64 KiB) Viewed 6201 times

Love the project though. Will likely make one once it's all sorted.

I was actually wondering about the possibility of using your logic to create a logic based ULA board with SMD components. It might be possible to make it small enough to cram it in to a ZX81 as another replacement option.

[PokeMon]

A NAND gate with inverted inputs and inverted output is logically the same as an OR gate.
Personally I prefer using an OR symbol rather than an AND symbol with all inverted.

[mikeyp]

A NAND gate with inverted inputs and inverted output is logically the same as an OR gate.
Personally I prefer using an OR symbol rather than an AND symbol with all inverted.

Super, thank you for clarifying that for me.

[1024MAK]

A NAND gate with inverted inputs and inverted output is logically the same as an OR gate.
Personally I prefer using an OR symbol rather than an AND symbol with all inverted.

Super, thank you for clarifying that for me.

Where the input signals are active low, some people prefer to use this symbol as to them, it better illustrates the actual logic function.

My preference is the symbol for the logic function of the chip, that is, I agree with PokeMon.

Mark

[PokeMon]

Yes, I guess this is all a matter of preference.

[lowlevel]

The ZX-81+38 in operation
I have a revision 1.4 which is patched to revision 1.6.

ZX81+38 mit ZX-WESPI.jpg

This looks wonderful... Nice job! Has anyone in North America built one yet? I would very much like to build a 1.6... not expecting kicad files, but would be very fun to try a different layout, maybe add some doo-dads.

Hope all is well guys, take care.

[mahjongg]

I noticed there was no real BOM available on my GitHub pages for the ZX81+38, only an empty entry where the .ODF (open office spreadsheet) file should have been. I deleted the empty entry, and added the real .ODF spreadsheet file.
Note that the spreadsheet lists exactly which component to buy from the two sources that combined have all the needed parts, from Farnell and Mouser.
This prevents buying almost but not fully correct parts.

get the BOM here as ZX81plus38_BOM.ods at https://github.com/mahjongg2/ZX81plus38

Note that the ZX81+35 keyboard will also work with the ZX81+38, I have not yet made a specific ZX81+38 keyboard yet.