New ZX80 boards
Posted: Mon Mar 22, 2010 9:34 pm
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?
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?