New ZX80 boards

[Lee Hart]

Hello to all. I just joined and this is my first post.

I had a ZX80, and two ZX81's oh so many years ago. Sadly, they died and I foolishly discarded them. Lately, I've become interested again in returning to those "thrilling days of yesteryear", when Dr. Dobbs preached of "running light without overbyte", and when I could actually understand how the computer worked and program it myself.

The prices for a real ZX80 seem to be outrageous; and, they are now so old that operation is questionable. But I ran across Grant Searle's marvelous website, which fully documented the ZX80. So, as I am an electrical engineer, I decided I could build my own!

I tweaked the circuit a bit to use modern CMOS parts (to save power) and bigger memory chips (a 32k RAM and EPROM, of which 16k of each is available). I used real tactile keyswitches (as the keyboards were a major weak point on my old machines). I replaced the RF modulator with a simple direct video output. I kept the original bus edge connector, but added a 50-pin header with all the same pins (a stronger, more reliable connector; the old bus connector was a pain in the you-know-what). The extra pins in this connector bring out all the signals so Grant Searle's ZX81 conversion circuit can plug right in, without cutting any traces or dangling wires. Finally, the Mic input and Ear output are retained, but they also have RS-232 level converters, for connection to a PC's serial port.

I then laid out the PC board. It's the same physical size as the original, with the same connectors and locations. It should even fit the original case, though I don't have one to be sure.

The nature of PC boards is that it is prohibitively expensive to order just one. So, I'm wondering how many I should order? I usually get them from Advanced Circuits, on their "3 for $33" specials. More boards brings the price per board down, but I (personally) don't need more boards.

I got to thinking. Are there other people still interested in the ZX80? A little Googling led me here. I was surprised to see quite a bit of activity!

So, this has been a rather long first post. But, I wonder if anyone else would be interested in a ZX80 bare board. I figure I'll just divide up the cost between however many we wind up getting. In return, I'd like some help testing and debugging it, and ideas for where to go from here.

Anyone interested?

[superfo]

yes, i'm interested.

[nama]

Possibly, yes!

[sirmorris]

+1!

[RWAP]

I would be interested from a market point of view - there could well be a new market for this type of computer - particularly with the edge connector fixed!

[Lee Hart]

Three responses... I'm impressed! I guess that means it is safe to order at least 4 boards. I'll get pricing on various quantities so we know what effect it has on price.

Rich says there might be "a market"? I'm amazed! But I wonder about the ethics of making it a commercial product. I imagine the ZX80 design was copyrighted, patented, or otherwise protected. In the US, it is legal to make a copy of such things for your own personal use, but you can't sell them. Any profits ethically belong to the originator (Uncle Clive?)

[zx81jens]

Hi Lee!

I´m from the german ZX-TEAM (see: http://www.zx81.de) and looking forward to have two of the new ZX80. Also, i´ll ask the german members for orders. In my opinion there is interest.

Is it possible, that you send the circuit´s to germany? I´ll send you money then (for your expenditure)...

Give me an answere, please.

Greetings
Jens

[Shaun_B]

Hi,

I'd be interested in a board. Regarding the (C), well if it's an exact ZX80 clone then there's a problem. I think Amstrad (who own Sinclair's IPs) said that ZX Spectrum clones could be legal as long as the ROM/OS was stored 'softly', ie, on disk or removable media, rather than being in a ROM.

Regards,

Shaun.

[Lee Hart]

To Jens:

Yes, I can send you the schematic. What is your email address? For that matter, does this board have a "files" section where I should post the schematic so all can see or critique it? More eyes might find problems or improvements.

To Shaun:

It's not an exact copy of the original, but should be functionally identical. I even made the board the same size, with the chips in the same places, same mounting holes, etc. The only changes were to use newer chips (74HC vs. 74LS), bigger RAM (6264 8k or 62256 32k vs. two 2114), a generic EPROM instead of a custom mask ROM (2732 or 2764), direct video instead of an RF modulator, and real keyboard switches instead of the membrane keypad. From a hardware perspective, I would think this avoids any direct copyright infringement.

From a software perspective, one could plug an original ZX80 or ZX81 ROM into it to be completely legitimate. But there are also a number of derivative ROMs that could be used (and would actually be better for some purposes).

To sell them commercially, I think a lawyer would have to look into it to see what is OK to copy and what is not. I'm no expert in that area.

[RWAP]

To Jens:

Yes, I can send you the schematic. What is your email address? For that matter, does this board have a "files" section where I should post the schematic so all can see or critique it? More eyes might find problems or improvements.

To Shaun:

It's not an exact copy of the original, but should be functionally identical. I even made the board the same size, with the chips in the same places, same mounting holes, etc. The only changes were to use newer chips (74HC vs. 74LS), bigger RAM (6264 8k or 62256 32k vs. two 2114), a generic EPROM instead of a custom mask ROM (2732 or 2764), direct video instead of an RF modulator, and real keyboard switches instead of the membrane keypad. From a hardware perspective, I would think this avoids any direct copyright infringement.

From a software perspective, one could plug an original ZX80 or ZX81 ROM into it to be completely legitimate. But there are also a number of derivative ROMs that could be used (and would actually be better for some purposes).

To sell them commercially, I think a lawyer would have to look into it to see what is OK to copy and what is not. I'm no expert in that area.

1) The question over the files - no there is not a files section, but you can upload the image as an attachment - when creating a message below the Save | Preview | Submit buttons there is a tab for Upload Attachment.

2) As for copyright infringement - the simplest thing to do would be to approach Sinclair / Amstrad - not sure if Amstrad purchased the rights to the ZX80 ! However, you are not making an exact copy of the original - it will be functionally the same, but you will have your own circuit board and off the shelf chips - software has to undergo a "look and feel" test, but not hardware for copyright infringement. The only custom chip would be the ROM and ULA - I presume the ZX80 has a ULA?

Arguably it would be better if the ROM could be minimal and load the o/s from a memory card (maybe using the SD/MMC interface Sirmorris is working on) - then it could be used to run as a ZX80 or ZX81 using one of the various online ROM images!!