This brings back memories - this was also my first computer as a kid! The kit was £79 and I saved up for 3 months to get it!! Spent hours soldering all the ICs - and then hours fixing all the dry solder joints. Then bought the ZX81, Spectrum and the Sinclair QL. Sadly had to get rid of them when I moved to US. I brought my Memotech MTX512 though!
Just a word of appreciation. Thanks very much for sharing all this beautiful work! An aesthetic example. Enthusiastically and really well put together ZX80 project!
Just another viewer appreciation note: ... I mean YOU HAVE REKINDLED an old passion i had years ago in building up electronics projects.... I've even gone out and bought new PCB making gear, cleared out a spare room and have made a workbench and unpacked my stored away electronics tools etc! I've Subscribed and working through almost all of your videos so far the DC Load is on my 1st list 'ToDo' hunting down parts and coming up to speed on Arduino. Your excellent description of a design makes it easy to understand what the circuit is doing... Can't wait for many more videos.... Thank you, thank you so much.
Nice to hear its rekindled your old passion. I am currently working on Part 7 to my DC Load project with some updates and the option of a single PCB design for the whole project. Hope to get the filming finished soon so I can up load it to my You Tube channel. Thanks for your comments. Regards, Louis
The ZX81 was my 1st computer. I think I had 4 at one time. Only 1 now and it still works. I made modifications to them to use extra memory in the basement / a modified xt keyboard / video inverter switch and a big-azz rubberband to hold the 16K Ram Pak on. Thanks for the vid.
Thanks for your comments. I remember the issues with the 16KByte memory pack. Unless you secured it it tended to be loose and you sometimes lost memory contents. I used Velcro on mine to hold it firm.
Yes. I upgraded to velcro(TM) also. People who "Thumb Down" videos should have to state "why" before it is logged. I see no reason to thumb down a fine video like this. Thanks again.
Hi Louis... Now that takes me back a bit. A mate bought a ZX80, I got the a ZX81 as the start and after 2 weeks, a 16k expansion pack and the thermal printer, sold it all at the Telford Radio Rally, then bought a Dragon32, then a Dragon 64, to which I added OS-9/6800, a home brew 1772 HD controller and 2 huge 5" full height Rodime Hard drives; with the whopping capacity of 5MB and 10MB respectively. They power supply was astounding, it needed around 10/5v and 10A/12v to spin those monsters and the SA400 card to drive them. Oh heady / happy days, it takes me back to the very start, Lovely nostaligia trip, well done... Thanks...
Thanks for the comments Martin. Agree, they were happy days. I move on from the ZX80 to a Ohio Supperboard with 4K of RAM and then on to a BBC Model B Computer. I still have both of these. Regards, Louis
It was my first computer as well... with 16 Kb memory expansion and a cheap tape recorder for storage. It lead to learning basic programming and ultimately a career with Microsoft etc. It was the best investment I ever made... for that reason alone I'll build one. The second coming so to speak... Thanks for sharing! :)
Thanks Yann. The ZX80 was also what I learned programming on. Interestingly the original ZX80 are now quite rare and good ones sell on eBay for upto £499. I recently found this PCB and though I have to build one. I have since had lots of fun using it and remembering the good old days when not only could you build one yourself but you could understand it to. Regards, Louis
Nice video. My first computer was a ZX81. I used it for a short while but the resonator perished. I never found a replacement. However, I did go on to get a 48K Spectrum which I used for ages.
It is beautifully made, not only the case and the mix of old and new, the ZX80 and ZX81, but also the new PCB with extra RAM and multiple ROMs. This is an improvement to what was already there. For the next version of the board you could go to 32K or 48K of RAM. It's good work!
Thank you for your for making this detailed video. The ROM image selection part helped me out with another project by saving me from having to hunt down 27c64s. I was able to use the more common 256's thanks to this.
Plus, as the key"board" doesn't seem too complex, it would open the path to make a much nicer input device for the wee computer. Printing keys would be a very simple task for such a machine indeed.
Very nice build & conversion!, and always great to see more ZX80/81/Spectrum on the web so much congrats. I started with a borrowed ZX81 back in the day, got the bug and bought a Spectrum and never looked back.....:)
Thanks Ian. I was like you but moved on from a ZX80 to a Ohio Superboard and then to a BBC Model B Computer. Is still have these and they are still working. Thoughs were the days when you understood what was going on in a PC :) Regards, Louis
I really enjoyed this tutorial and thank you for providing all the info and links so we can build our own. Your version is much nicer than the original...
A little gem from the good old days, when Britain was on the forefront of computer technologies. Had a ZX81, an Amstrad CPC664, later am Achimedes, all of which unique and fascinating machines from the UK. And when the Atari STs hit the scene it was again a UK company, INMOS, that reeled me in with their transputers. Though being from Austria, I miss the days when Britain had a significant say in the digital realm :) Good show, thanks for sharing!
Only just watching this. I hope you did not tear down that old ZX81 board. It is likely that all that was wrong with the unit was the keyboard flex and you can trim off the cracked sections with scissors and use the shorter tails to insert into the pinch connectors. That was how I recovered an old Timex Sinclair 1000. Unfortunately, further disassemblies to repot the heatsink for the regulator and swap out the electrolytic caps for ceramic caused the flexes to crack further. Fortunately, Tynemouth Software to the rescue and I ordered a ZX81 keypad with TS1000 overlay!
What a great little project! Thanks for making me aware of this, the ZX81 was my first computer and I spent hours and hours typing in code, only for the RAM pack to wobble, crashing the machine and forcing me to start typing all over again. Ah memories!
I still have my ZX80, opened it and discovered that it's missing 2 ICs both are 7400, probably years ago I needed them for some project. Surly I wouldn't do such thing today, I'm going to put back the missing ICs, shame they would be of new vintage though.
wow. this takes all the mystery out of these little Sinclair's 🧐 i almost purchased one of these when they came out, but went with ibm dos pc😵💫 a wonderful project video 🥳👌🍰☕
Very cool, Louis. I actually had a Timex/Sinclair ZX81 as a kit in my youth also. Brings back fond memories. I may have a go at building this project. Oh and BTW I have not given up on the DC load PCB, just been busy and now that the summer weather approaches it is really hard to stay indoors and look at a screen for hours. I will get back to that project as well. Thanks for the memory.
It's worth mentioning that many ZX81's listed as "faulty" on eBay are not, it's just that modern TV's have a problem resolving the ZX81's rather wonky RF output. Also, the ULA (custom IC) in the ZX81 is no longer available, so worth keeping hold of or passing to a ZX81 enthusiast.
This is the machine/kit I recommended to a friend who wants to get a general understanding for 8bit architectures (while I got myself a Pentagon 48K PCB from the same seller). I wonder how hard it's gonna be to add the ZX81 'fast'-mode later on.
I reverse engineered the ULA of a ZX-81 and designed a PCB of the whole ZX-81 a clone that is 100% compatible with the Z81 PCB, as in it can replace the PCB of a real ZX-81, it fits inside the ZX-81 case (or a 3D printed replica). It uses only simple to solder and readily available components. So you can build a ZX-81 clone without needing an ULA, with only common (HCT) TTL logic. My clone is called ZX-81+38 (as in 38 years after 1981) it has proven to be very compatible, and it outputs composite video through an RCA connector (that replaces the RF modulator output) compatible with modern TV's that have a yellow RCA video input. It is powered with a 500mA USB power supply through a mini USB-B port, and there are also 3.5mm audio jacks for cassette output and input. My cassette input circuit is much more sensitive than the original ZX-81 which needs a very loud audio signal to work reliable. as it has a built in pre-amplifier. my clone also has a DB9 input port for a standard (atari) Joystick, which "presses" the cursor keys, and the "fire button" key "0". for games. You can download the PCB production files (gerber and drill files) from my GitHub page, here: github.com/mahjongg2/ZX81plus38 anyone can use these files to create his own PCB's, and assemble it with a BILL of material (BOM) spreadsheet file, and the ZX-81 ROM file can be found online, and be programmed into a cheap 27C256 OTP (EPROM), more information can be found on my wiki page here: revspace.nl/ZX81plus38_simple_to_build_ZX-81_clone. So if you want to build your own ZX-81, check my clone out, P.S. now (july 2022) I released version 1.7 of my clone, which has a few enhancements: a better crystal oscillator, and a corrected connector for the keyboard. It is also made compatible with an enhanced ZX-81 ROM so that it can contain the firmware for my programmable sound board expansion with SD-card reader, coming soon. In august 2022, I launched what s perhaps my final version, revision 1.8. I also released the KiCad files, so its now full opensource. Version 1.9 repairs a small bug in the joystick to keyboard interface, it adds necessary pull down resistors on the bases of the 2N3904 transistors that simulate a keypress. I'm busy with my own version of the ZON-X81 programmble sound generator, that also has logic for an SD-Card, and software exists in a ROM expansion, so with a simple command you can launch a menu with which you can pick with a single letter from a to z one of 26 possible games. Loading from sd-card is ten times faster than from cassete.
Interesting. Sucks that back in the day for a few pennies Sinclair could have used a slightly larger Rom that would have allowed the character set to be changed with a User defined one for better graphics.
On the original zx80, the keyboard was integrated into the PCB. The original case looked a lot like it was vacuum formed whereas the zx81 case was injection molded. Anyhow, this was an interesting project. The zx80 was my first computer like a lot of people. I feel foolish now because I sold it to buy a zx81. I still have the original manual and schematic. I found this video because I am looking to re-purpose an old Timex 2040 printer.
The original Sinclair ZX80 now sell for high prices on eBay. There must be a lot of collectors out there. They are also hard to come by in good condition. The Timex brand name was used in the USA I believe. Regards, Louis
Originally, Sinclair sold the ZX80 and ZX81 directly in the US. There were magazine ads in Popular Electronics and such. I bought my ZX80 as a kit and later upgraded to the 8K ROM. When I sold it, I gave the buyer the new 8K manual, but kept the old 4K ROM and manual. The ZX80 was not capable of SLOW mode which is what I wanted. Once I saw what SLOW mode actually was, I felt really dumb for selling the ZX80 like that. That was back in 1981 or so. Sinclair should have renamed FAST and SLOW to "INCREDIBLY SLOW" and "RIDICULOUSLY SLOW", but I guess he was trying to save bytes.
I still have a fascination with BASIC. Back then I had all of the Tandy color computers, a Timex/Sinclair, Commodore VIC 20 and 64, Dragon Color computer, Odysey and I can't remember the rest
Very nice bit of "whiteboard work" you've got there! It's funny the ZX80 had that, to be honest, rather crappy, plastic case... but it looked FABULOUS.... like something from the future... future... future! I don't think any other computer has ever looked quite so "sci-fi". Back in t'old days my mate's ZX80 had a "ZX81-mode" toggle switch and my other mate's ZX81 had "user-defined characters" and "inverse video" toggle switches... So a wad of toggle switches down the side just add more authentic early 1980s styling to the project any way.
Hi Michael, This project also took me back to my early days of computer programming when you could do quite a lot with just 1K of RAM memory !!!! Regards, Louis
Very nice job Louis! I still have my original Apple II and learning how to write assembly language code is on my bucket list (Why? Not really sure!). BTW, your DC load project is being duplicated x5 by group of local hams (think they've been in touch with you directly); glad I pointed them in your direction.
Thanks Dino. Back in the 1980's I use to do assembly language with a 6502 CPU and did some teaching on it. Long time ago now :) I am still looking at a few tweaks to the DC Load Project following some good feedback. Regards, Louis
You are great, no I mean *REALLY GREAT*, did you know that? Amazing, interesting video from such a nice man. God bless you my friend, I mean it, you are AWESOME, and thank you for all the hard work you've put into your channel - bless you Sir. Matthew, UK.
Perhaps it might be better to mount the switches on the back of the case. There is a lot more room there to mount & group the switches. Depending upon the size of the ROM module, one two or three switches could be used for ROM partition selection (A13, A14, A15.) Mounting the switches would not spoil the lines of the case sides, but would still be easily accessible when required.
I have a ZX80 and you missed out the label on the front of the command words that needed to be actually spelt out. I noticed that they were also on the PCB silk. I used a 62256 Static RAM, back in the 1980's, to build a 32 K.Byte RAM pack. It cost a lot of money back in the 1980's for just one memory chip. I used a 74138 3 of 8 decoder to address it and having 32 K.Bytes of RAM to play with was great when it came to programming. On the downside saving and loading took twice as long as the ZX80 and ZX81 save the entire contents of RAM. Another factor was that any programme, no matter what the size under 16 K.Bytes, written and saved with the 32 K.Byte RAM pack attached wouldn't load when running a 16 K.Byte RAM pack, for obvious uniquely ZX80 and ZX81 reasons. This led to a switch being added to the RAM pack to set it into 16 K.Byte or 32 K.Byte modes before starting up the computer. I also ran the Memotech external proper full travel keyboard, Memotech RS232 module, Maplin port extender and 2 x Maplin tripple port IO cards. I still have my ZX80 and ZX81 so might set it up sometime and show my now 28 year old son and 16 year old nephew how we used to "Rough it" in the early days of home computing. having a ZX80 and ZX81 and building my own attachments gave me valuable experience. So many years later, when asked to design a bespoke IO card to drop into a PC it was a doddle.
Yes Timex Corporation had a joint venture in the USA to manufacture the Sinclair ZX80 and as such it was re-branded Timex Sinclair 1000 (TS1000). The TS1000 was a slightly modified Sinclair ZX81 with an NTSC RF modulator instead of a UK PAL modulator. I think it was launched in the US in July 1982. Regards, Louis
Very interesting project. I built a ZX80 back in the day when you could opt for a build it yourself from parts. But I quickly moved into the fantastic World of Dragon 32. You said that the XZ81 you bought was faulty, maybe it was just the keyboard ribbon cable & you could have got it working with a replacement part??
I should just mention that if you do build it try and use logic IC's of the 74LS version. I think the 74HCT type may work but when I tried to use 74HC type I had issues and it did not work.
Yes, HC is evil. The logic levels are CMOS, not TTL, so something like the ZX80 circuit which relies on the analogue properties of the digital circuits is more conscious of those levels. HCT does work, but LS is more authentic, and all parts are still in production.
+Dave: I actually belive HC would work for most (if not all) of the circuits. I strongly suspect either the clock oscillator" or it's two peculiar 470/47pF HP-filters, i.e. that these must be adjusted for CMOS-levels and currents. That "resistor multiplexer" on the data bus would be another (less likely) candidate. The diodes for the keyboard are very unlikely a problem. All the 1K ohm pullups could be a bit larger though, as HC/HCT draw less input current than do LS. (Where else are analogue properties employed? Haven't studied the schematic since the 1990s).
As well as the clock and delayed clock lines, and the databus sharing you mentioned, the video mixing levels would also need to be changed, and some of the ear/mic circuitry. I'll rephrase what I said if you like. The circuit as is, with the values suggested, will work with LS chips. You should be able to use HCT chips for most parts. If you use HC chips you may need to adjust several component values. There are also several parts which may not be available in HC or HCT varieties. All are currently in production in LS versions. So you might be able to get it working with HC chips. You should be able to get it working with HCT chips. You will be able to get it working with LS chips, which is what I would recommend.
Yes, the video and tape interface would need an adjustment as well, using HC. But what do you mean by "delayed clock lines"? There are nothing like that in the ZX80. The two HP-filters on the clock that I mentioned are quite the opposite to a delay. I agree authentic circuits are cooler, but as long as you don't use CPLDs, FPGAs or similar, but ICs that were around in the 1980s, it's good enough for me, by a large margin. ;-)
After getting it out of storage, it turns out my memory is bad:-( It's a Timex Sinclair 1000. The PCB looks almost exactly the same. It does work though.
As an American who has always wanted an original one of these but never got one, I couldn't help but notice the NTSC jumper on this PCB. Will it maintain PAL software compatibility with that? Do I need a different crystal?
Thanks. It was just a trip down memory lane :) In the 1980 not only could you build a small PC with a bunch of components it was also easier to understand how it all worked !! The ZX80 is still handy for learning Basic Programming. Louis
+Scullcom Hobby Electronics Very nice! I think it's a good idea to go back to the dc load again one day. I'm wondering if I can suggest something, the project had been updated several times and became a little complicated! Is it possible to make a video so you gather everything together and maybe a final clear schematic with a little explanation? And THANK YOU
HI Tom, I plan to go back to the DC Load and produce a new schematic. I also want to cover some of the changes as a result of all the feedback. Hopefully, I will get back to it soon. Regards, Louis
I heard the Z-80 stopped production. Does that mean the ZX/Sinclair hobby scene is going to be hampered? Or has someone made an FPGA replacement of the Z-80?
😁Americans do not understand the phenomenon of this computer, ZX80_ZX81, is a simple controller for robots, available for sale since the 1980s, in the form of various kits for self-assembly. Of course, there were also the schematics and self-collection of integrated circuits. hahaha And those connecting integrated circuits with cables when there was no PCB. 🤣🤣🤣That's probably longer than the United States has been around ...
This is my kind of project. I'm a bit surprised you didn't mention the possibilities for those of us familiar with Z80 machine code to actually "spin" our own ROM for this project or is that a future project you have in mind?
This is probably not the best hardware to use to spin your own Z80 code, as the CPU spends most of it's time drawing the screen, which you would have to replicate. Better go for the excellent RC2104 series of kits if you want to write Z80 code.
Interesting video. I still have my fully working ZX81 (modified with internal 32K static ram which 16k are available). But the keyboard membrane is starting to show its age. Thanks for the links for ordering a new one. BTW, the audio auto-level setting in the camera isn't performing very well. The constant limiter "pumping" effect is rather unpleasant. Maybe you could set the audio level manually ?
Excellent video and thank you. One question: As far as switching the ROM images go, wasn't there a different Ferranti PLA used in these computers or doesn't that make a difference?
The ZX81 used a Ferranti ULA to replace the glue logic used in the ZX80 (and this clone) thus reducing the chip count to the 4 ICs seen in the video. The official 8K BASIC ROM UPGRADE kit consisted of a replacement ROM, a keyboard overlay and the ZX81 programmers manual. This effectively gave the user a ZX81 without the hardware updates such as the NMI controlled slow mode or the edge connector changes needed to make it fully ZX81 compatible.
Very interesting! I was looking for any instructions about how to build a computer which isn't based on or descended from the IBM PC. This would involve making a custom PCB, or perhaps starting with a breadboard. Any information would be appreciated. What about a custom Z80 or 6502 computer with graphics? How did Apple and other companies make their first computers working from a garage? This project would have been much better if you hadn't used a ready made PCB, or an old ZX81 case. Why don't you show us how Soviet clones of the ZX Sinclair Spectrum were made? I've seen videos of the Kiwi computer, which is like a computer from a parallel universe, containing various chips from the 1980s and early 1990s, including an MSX2 or MSX2+ graphics chip (Yamaha V9938 or V9958), 68008 CPU, two Commodore SID chips, a custom case, and booting up using 68K BASIC or EmuTOS. Good luck with your channel, anyway!
Vad kul! Jag köpte en Z81 1981 eller 1982 när jag gick andra respektive tredje året på KTH. Det var början på mitt dataintresse... Kanske skall man bygga en kopia (om tiden räcker till). Jag tycker att Scullom är jätteduktig och visar helintressanta projekt där han tillverkar egna instrument med egna kretsort mm.
Thanks for your comments. My Swedish is not very good but understood what you said. Regards, Louis FOR ANYONE ELSE THE TRANSLATION OF ROBERTS COMMENTS I THINK: Good fun! I bought a ZX81 1981 or 1982 when I went to the second and third year at College. It was the beginning of my computer studies. Maybe you should build a copy (if the time is right). I enjoy your projects.
When I did mine, I had started with a pretty beat up ZX81 case which had marks and scratches on that made it not really suitable to be a ZX81 any more. I was able to sand off all those marks before spraying and brought it back into use. Some pictures on the original blog post: blog.tynemouthsoftware.co.uk/2017/02/minstrel-zx80-clone-issue-23-boards.html
@jorg,why not plenty of dead and dying examples of the zx81 out there, thats what i do i build bespoke units using single board computers, i build them into dead 80's machines with keyboard conversions, people seem to love them. i do repair/upgrade original stuff too, but wont use working examples to build customs that is my only rule, if you want a pc putting in an old computer it has to be a dead example, loads of dead stuff out there cheap without killing good ones.
I would imagine the replacement keyboard is also better quality than the original since it's made by a company which makes them for scientific and medical equipment.
![[LIVE] : ONE ลุมพินี 88 | คู่เอก "ป้อมเพชร vs อัสลามจอน"](http://i.ytimg.com/vi/1ZqTVVbMgbo/mqdefault.jpg)
This brings back memories - this was also my first computer as a kid! The kit was £79 and I saved up for 3 months to get it!! Spent hours soldering all the ICs - and then hours fixing all the dry solder joints. Then bought the ZX81, Spectrum and the Sinclair QL. Sadly had to get rid of them when I moved to US. I brought my Memotech MTX512 though!
Thanks for the memories :)
Just a word of appreciation. Thanks very much for sharing all this beautiful work! An aesthetic example. Enthusiastically and really well put together ZX80 project!
Thank you.
Just another viewer appreciation note: ... I mean YOU HAVE REKINDLED an old passion i had years ago in building up electronics projects.... I've even gone out and bought new PCB making gear, cleared out a spare room and have made a workbench and unpacked my stored away electronics tools etc! I've Subscribed and working through almost all of your videos so far the DC Load is on my 1st list 'ToDo' hunting down parts and coming up to speed on Arduino. Your excellent description of a design makes it easy to understand what the circuit is doing... Can't wait for many more videos.... Thank you, thank you so much.
Nice to hear its rekindled your old passion. I am currently working on Part 7 to my DC Load project with some updates and the option of a single PCB design for the whole project. Hope to get the filming finished soon so I can up load it to my You Tube channel.
Thanks for your comments.
Regards,
Louis
I had a ZX81 - bought as kit - and I build myself a 32KByte DRAM extension for it. You did a very nice job, sir!
The ZX81 was my 1st computer. I think I had 4 at one time. Only 1 now and it still works.
I made modifications to them to use extra memory in the basement / a modified xt keyboard / video inverter switch and a big-azz rubberband to hold the 16K Ram Pak on. Thanks for the vid.
Thanks for your comments. I remember the issues with the 16KByte memory pack. Unless you secured it it tended to be loose and you sometimes lost memory contents. I used Velcro on mine to hold it firm.
Yes. I upgraded to velcro(TM) also. People who "Thumb Down" videos should have to state "why" before it is logged. I see no reason to thumb down a fine video like this. Thanks again.
lapel mic helps a lot. Thank you for your service! Good audio is worth the extra little hassle.
This video takes me back to my childhood. And it's so well explained. You deserve a statue.
Hi Louis... Now that takes me back a bit. A mate bought a ZX80, I got the a ZX81 as the start and after 2 weeks, a 16k expansion pack and the thermal printer, sold it all at the Telford Radio Rally, then bought a Dragon32, then a Dragon 64, to which I added OS-9/6800, a home brew 1772 HD controller and 2 huge 5" full height Rodime Hard drives; with the whopping capacity of 5MB and 10MB respectively. They power supply was astounding, it needed around 10/5v and 10A/12v to spin those monsters and the SA400 card to drive them. Oh heady / happy days, it takes me back to the very start, Lovely nostaligia trip, well done... Thanks...
Thanks for the comments Martin. Agree, they were happy days. I move on from the ZX80 to a Ohio Supperboard with 4K of RAM and then on to a BBC Model B Computer. I still have both of these.
Regards,
Louis
It was my first computer as well... with 16 Kb memory expansion and a cheap tape recorder for storage. It lead to learning basic programming and ultimately a career with Microsoft etc. It was the best investment I ever made... for that reason alone I'll build one. The second coming so to speak... Thanks for sharing! :)
Thanks Yann. The ZX80 was also what I learned programming on. Interestingly the original ZX80 are now quite rare and good ones sell on eBay for upto £499. I recently found this PCB and though I have to build one. I have since had lots of fun using it and remembering the good old days when not only could you build one yourself but you could understand it to.
Regards,
Louis
Nice video. My first computer was a ZX81. I used it for a short while but the resonator perished. I never found a replacement. However, I did go on to get a 48K Spectrum which I used for ages.
It is beautifully made, not only the case and the mix of old and new, the ZX80 and ZX81, but also the new PCB with extra RAM and multiple ROMs. This is an improvement to what was already there. For the next version of the board you could go to 32K or 48K of RAM. It's good work!
Thank you for your for making this detailed video. The ROM image selection part helped me out with another project by saving me from having to hunt down 27c64s. I was able to use the more common 256's thanks to this.
Very nice! Instead of using unreplaceable original ZX 80 cases, 3D printed ones would be a good idea, though.
Thanks. 3D printing would be an option as ZX80 cases are hard to come by.
Plus, as the key"board" doesn't seem too complex, it would open the path to make a much nicer input device for the wee computer. Printing keys would be a very simple task for such a machine indeed.
Nice work. I still have my KIM-1 and ZX Spectrum working. The Spectrum had a floppy interface and light pen back in 1986. It was also running FORTH.
Wow; your video presentation was REALLY Really really good 👍🏿 Thank GOD 🙏🏾 and thank you very much for sharing your support and time 😉
Very nice build & conversion!, and always great to see more ZX80/81/Spectrum on the web so much congrats. I started with a borrowed ZX81 back in the day, got the bug and bought a Spectrum and never looked back.....:)
Thanks Ian. I was like you but moved on from a ZX80 to a Ohio Superboard and then to a BBC Model B Computer. Is still have these and they are still working. Thoughs were the days when you understood what was going on in a PC :)
Regards,
Louis
I really enjoyed this tutorial and thank you for providing all the info and links so we can build our own. Your version is much nicer than the original...
That takes me back. My first electronic kit was a keyboard replacement from Maplin for the ZX81.
Good old days :)
I had one of them then bought the Time 1000 and the 1500 along with extended memory modules, printer and modem and eventually sold all of them.
A little gem from the good old days, when Britain was on the forefront of computer technologies. Had a ZX81, an Amstrad CPC664, later am Achimedes, all of which unique and fascinating machines from the UK. And when the Atari STs hit the scene it was again a UK company, INMOS, that reeled me in with their transputers. Though being from Austria, I miss the days when Britain had a significant say in the digital realm :) Good show, thanks for sharing!
Thanks for your comments. As you say they were the good old days.
Regards,
Louis
Only just watching this.
I hope you did not tear down that old ZX81 board. It is likely that all that was wrong with the unit was the keyboard flex and you can trim off the cracked sections with scissors and use the shorter tails to insert into the pinch connectors.
That was how I recovered an old Timex Sinclair 1000. Unfortunately, further disassemblies to repot the heatsink for the regulator and swap out the electrolytic caps for ceramic caused the flexes to crack further. Fortunately, Tynemouth Software to the rescue and I ordered a ZX81 keypad with TS1000 overlay!
Excellent video. Thank you for walking us through the build process.
Thanks Martin.
What a great little project! Thanks for making me aware of this, the ZX81 was my first computer and I spent hours and hours typing in code, only for the RAM pack to wobble, crashing the machine and forcing me to start typing all over again. Ah memories!
Thanks.
Ah. The dreaded Rampack wobble. That brings back memories.
Very good explanation of memory arrangement. I wish some one made such explanation of the logic circuits as well.
My first computer was a Sinclair 2068. Great job!
I still have my ZX80, opened it and discovered that it's missing 2 ICs both are 7400, probably years ago I needed them for some project. Surly I wouldn't do such thing today, I'm going to put back the missing ICs, shame they would be of new vintage though.
I have done the same myself at times on other equipment when needing a part.
This is really an outstanding project. I'm about to assemble a minstrel kit. Thank you for providing this information.
wow. this takes all the mystery out of these little Sinclair's 🧐 i almost purchased one of these when they came out, but went with ibm dos pc😵💫 a wonderful project video 🥳👌🍰☕
Paint? Black is the best color! It doesn’t yellow! Bang up job. :)
Very cool, Louis. I actually had a Timex/Sinclair ZX81 as a kit in my youth also. Brings back fond memories. I may have a go at building this project. Oh and BTW I have not given up on the DC load PCB, just been busy and now that the summer weather approaches it is really hard to stay indoors and look at a screen for hours. I will get back to that project as well. Thanks for the memory.
Thanks Rob. I know what you mean, when the weather is hot its normal to spend more time outside.
Sheer dedication. Outstanding tutorial showing how it should be done! - when did Michael Cain get into Electronics lol
Thanks. I smiled at you Michael Cain comment :)
Damned, after seeing your video I need to build one like yours. I really like it. Thanks for sharing 🙏🏻
It's worth mentioning that many ZX81's listed as "faulty" on eBay are not, it's just that modern TV's have a problem resolving the ZX81's rather wonky RF output. Also, the ULA (custom IC) in the ZX81 is no longer available, so worth keeping hold of or passing to a ZX81 enthusiast.
This is the machine/kit I recommended to a friend who wants to get a general understanding for 8bit architectures (while I got myself a Pentagon 48K PCB from the same seller). I wonder how hard it's gonna be to add the ZX81 'fast'-mode later on.
Great !!! And now must be assembled ZX-Spectrum !!!
I reverse engineered the ULA of a ZX-81 and designed a PCB of the whole ZX-81 a clone that is 100% compatible with the Z81 PCB, as in it can replace the PCB of a real ZX-81, it fits inside the ZX-81 case (or a 3D printed replica). It uses only simple to solder and readily available components.
So you can build a ZX-81 clone without needing an ULA, with only common (HCT) TTL logic. My clone is called ZX-81+38 (as in 38 years after 1981) it has proven to be very compatible, and it outputs composite video through an RCA connector (that replaces the RF modulator output) compatible with modern TV's that have a yellow RCA video input. It is powered with a 500mA USB power supply through a mini USB-B port, and there are also 3.5mm audio jacks for cassette output and input. My cassette input circuit is much more sensitive than the original ZX-81 which needs a very loud audio signal to work reliable. as it has a built in pre-amplifier. my clone also has a DB9 input port for a standard (atari) Joystick, which "presses" the cursor keys, and the "fire button" key "0". for games. You can download the PCB production files (gerber and drill files) from my GitHub page, here: github.com/mahjongg2/ZX81plus38 anyone can use these files to create his own PCB's, and assemble it with a BILL of material (BOM) spreadsheet file, and the ZX-81 ROM file can be found online, and be programmed into a cheap 27C256 OTP (EPROM), more information can be found on my wiki page here: revspace.nl/ZX81plus38_simple_to_build_ZX-81_clone. So if you want to build your own ZX-81, check my clone out,
P.S. now (july 2022) I released version 1.7 of my clone, which has a few enhancements: a better crystal oscillator, and a corrected connector for the keyboard. It is also made compatible with an enhanced ZX-81 ROM so that it can contain the firmware for my programmable sound board expansion with SD-card reader, coming soon.
In august 2022, I launched what s perhaps my final version, revision 1.8.
I also released the KiCad files, so its now full opensource.
Version 1.9 repairs a small bug in the joystick to keyboard interface, it adds necessary pull down resistors on the bases of the 2N3904 transistors that simulate a keypress.
I'm busy with my own version of the ZON-X81 programmble sound generator, that also has logic for an SD-Card, and software exists in a ROM expansion, so with a simple command you can launch a menu with which you can pick with a single letter from a to z one of 26 possible games. Loading from sd-card is ten times faster than from cassete.
Interesting. Sucks that back in the day for a few pennies Sinclair could have used a slightly larger Rom that would have allowed the character set to be changed with a User defined one for better graphics.
Such a great project! Keep being awesome, and thanks for sharing this!
Thanks Per.
Very well done cousin Louis brings back memories.
Great video. Question, what the "output" from the Z80 what gives video to the logic CCT section?
On the original zx80, the keyboard was integrated into the PCB. The original case looked a lot like it was vacuum formed whereas the zx81 case was injection molded. Anyhow, this was an interesting project. The zx80 was my first computer like a lot of people. I feel foolish now because I sold it to buy a zx81. I still have the original manual and schematic. I found this video because I am looking to re-purpose an old Timex 2040 printer.
The original Sinclair ZX80 now sell for high prices on eBay. There must be a lot of collectors out there. They are also hard to come by in good condition. The Timex brand name was used in the USA I believe.
Regards,
Louis
Originally, Sinclair sold the ZX80 and ZX81 directly in the US. There were magazine ads in Popular Electronics and such. I bought my ZX80 as a kit and later upgraded to the 8K ROM. When I sold it, I gave the buyer the new 8K manual, but kept the old 4K ROM and manual. The ZX80 was not capable of SLOW mode which is what I wanted. Once I saw what SLOW mode actually was, I felt really dumb for selling the ZX80 like that. That was back in 1981 or so. Sinclair should have renamed FAST and SLOW to "INCREDIBLY SLOW" and "RIDICULOUSLY SLOW", but I guess he was trying to save bytes.
This could easily be adapted to output NTSC standard video. Neat!
Yes should be easy.
Cool project! You did a fantastic job on it and I really enjoyed watching the build. Thanks!
Thanks.
Awesome! Quality Work Many Thanks!
Very interesting and informative video! Looks great at the end.
Thank you.
Very nicely done! Although I must say I am partial to the ZX 48K.
Thanks for your comment.
Nice equipments in the background !
Thanks.
What a superb video. Start to finish just amazing. Subscribed.
This is very interesting, thank you for sharing this.
I still have a fascination with BASIC. Back then I had all of the Tandy color computers, a Timex/Sinclair, Commodore VIC 20 and 64, Dragon Color computer, Odysey and I can't remember the rest
Thanks for your comments. Seems you had a large collection :)
Great video!
Thanks a lot.
Thanks.
Very nice bit of "whiteboard work" you've got there!
It's funny the ZX80 had that, to be honest, rather crappy, plastic case... but it looked FABULOUS.... like something from the future... future... future! I don't think any other computer has ever looked quite so "sci-fi".
Back in t'old days my mate's ZX80 had a "ZX81-mode" toggle switch and my other mate's ZX81 had "user-defined characters" and "inverse video" toggle switches... So a wad of toggle switches down the side just add more authentic early 1980s styling to the project any way.
They literally drew the copper tracks in those days, how wonderful it worked
Great Video... takes me back...looks very authentic
Hi Michael,
This project also took me back to my early days of computer programming when you could do quite a lot with just 1K of RAM memory !!!!
Regards,
Louis
Minor rectification @ 5:50 the upper part from the ram is being used because A14 is tied to 5V and not to ground.
A very nice video again. My first computer was the Spectrum.
Thanks Han. I never did have a Spectrum. I went on to an American Ohio Superboard using a 6502 CPU.
All I can say is that what you did was amazing! Thank you so much! :-)
Holy shit, that zx81 board looks hand drawn.
Very nice job Louis! I still have my original Apple II and learning how to write assembly language code is on my bucket list (Why? Not really sure!). BTW, your DC load project is being duplicated x5 by group of local hams (think they've been in touch with you directly); glad I pointed them in your direction.
Thanks Dino. Back in the 1980's I use to do assembly language with a 6502 CPU and did some teaching on it. Long time ago now :) I am still looking at a few tweaks to the DC Load Project following some good feedback.
Regards,
Louis
Great work! Enjoyed every second of the video!
What an exelent job you have done!
You are great, no I mean *REALLY GREAT*, did you know that? Amazing, interesting video from such a nice man. God bless you my friend, I mean it, you are AWESOME, and thank you for all the hard work you've put into your channel - bless you Sir.
Matthew, UK.
Thanks Matthew for your kind comment.
Regards,
Louis
Great fun, thanks for the detailed video, much appreciated.
Perhaps it might be better to mount the switches on the back of the case. There is a lot more room there to mount & group the switches. Depending upon the size of the ROM module, one two or three switches could be used for ROM partition selection (A13, A14, A15.) Mounting the switches would not spoil the lines of the case sides, but would still be easily accessible when required.
Thanks. Good idea. I have not drilled the holes yet so I will add the switches at the back.
Louis
Michael Cain builds a ZX80! Awesome - not a lot of people know that!
I have a ZX80 and you missed out the label on the front of the command words that needed to be actually spelt out. I noticed that they were also on the PCB silk.
I used a 62256 Static RAM, back in the 1980's, to build a 32 K.Byte RAM pack. It cost a lot of money back in the 1980's for just one memory chip. I used a 74138 3 of 8 decoder to address it and having 32 K.Bytes of RAM to play with was great when it came to programming.
On the downside saving and loading took twice as long as the ZX80 and ZX81 save the entire contents of RAM. Another factor was that any programme, no matter what the size under 16 K.Bytes, written and saved with the 32 K.Byte RAM pack attached wouldn't load when running a 16 K.Byte RAM pack, for obvious uniquely ZX80 and ZX81 reasons.
This led to a switch being added to the RAM pack to set it into 16 K.Byte or 32 K.Byte modes before starting up the computer.
I also ran the Memotech external proper full travel keyboard, Memotech RS232 module, Maplin port extender and 2 x Maplin tripple port IO cards.
I still have my ZX80 and ZX81 so might set it up sometime and show my now 28 year old son and 16 year old nephew how we used to "Rough it" in the early days of home computing.
having a ZX80 and ZX81 and building my own attachments gave me valuable experience. So many years later, when asked to design a bespoke IO card to drop into a PC it was a doddle.
Thanks Andy for a trip down memory lane. Regards, Louis
Times-Sinclair on this side of the pond, I think. :-)
I believe it was also available as a kit back then.
Yes Timex Corporation had a joint venture in the USA to manufacture the Sinclair ZX80 and as such it was re-branded Timex Sinclair 1000 (TS1000). The TS1000 was a slightly modified Sinclair ZX81 with an NTSC RF modulator instead of a UK PAL modulator. I think it was launched in the US in July 1982.
Regards,
Louis
Very interesting project. I built a ZX80 back in the day when you could opt for a build it yourself from parts.
But I quickly moved into the fantastic World of Dragon 32.
You said that the XZ81 you bought was faulty, maybe it was just the keyboard ribbon cable & you could have got it working with a replacement part??
Yes the ZX81 keypads are known to develop faults over time. But it was cheap to buy and I need a case.
I think I might build this
I'm very interested in the implementation of 74 series logic for the video output
I should just mention that if you do build it try and use logic IC's of the 74LS version. I think the 74HCT type may work but when I tried to use 74HC type I had issues and it did not work.
Yes, HC is evil. The logic levels are CMOS, not TTL, so something like the ZX80 circuit which relies on the analogue properties of the digital circuits is more conscious of those levels. HCT does work, but LS is more authentic, and all parts are still in production.
+Dave: I actually belive HC would work for most (if not all) of the circuits. I strongly suspect either the clock oscillator" or it's two peculiar 470/47pF HP-filters, i.e. that these must be adjusted for CMOS-levels and currents. That "resistor multiplexer" on the data bus would be another (less likely) candidate. The diodes for the keyboard are very unlikely a problem. All the 1K ohm pullups could be a bit larger though, as HC/HCT draw less input current than do LS. (Where else are analogue properties employed? Haven't studied the schematic since the 1990s).
As well as the clock and delayed clock lines, and the databus sharing you mentioned, the video mixing levels would also need to be changed, and some of the ear/mic circuitry. I'll rephrase what I said if you like. The circuit as is, with the values suggested, will work with LS chips. You should be able to use HCT chips for most parts. If you use HC chips you may need to adjust several component values. There are also several parts which may not be available in HC or HCT varieties. All are currently in production in LS versions.
So you might be able to get it working with HC chips. You should be able to get it working with HCT chips. You will be able to get it working with LS chips, which is what I would recommend.
Yes, the video and tape interface would need an adjustment as well, using HC. But what do you mean by "delayed clock lines"? There are nothing like that in the ZX80. The two HP-filters on the clock that I mentioned are quite the opposite to a delay.
I agree authentic circuits are cooler, but as long as you don't use CPLDs, FPGAs or similar, but ICs that were around in the 1980s, it's good enough for me, by a large margin. ;-)
I still have my original ZX-80 and a 16K memory module, it still works:-)
The original ZX80 are quick rare now and if it is good condition they can sell for up to £500. Nice investment :)
After getting it out of storage, it turns out my memory is bad:-( It's a Timex Sinclair 1000. The PCB looks almost exactly the same. It does work though.
Can you do one on testing + diagnosing a TS 1016 16K RAM pack.
As an American who has always wanted an original one of these but never got one, I couldn't help but notice the NTSC jumper on this PCB. Will it maintain PAL software compatibility with that? Do I need a different crystal?
We made this toy many times in 1980s.
Nicely done, can you explain why we would want to use a Z80. Aren't there more modern choices to learn on.
Thanks. It was just a trip down memory lane :) In the 1980 not only could you build a small PC with a bunch of components it was also easier to understand how it all worked !! The ZX80 is still handy for learning Basic Programming.
Louis
+Scullcom Hobby Electronics
Very nice!
I think it's a good idea to go back to the dc load again one day. I'm wondering if I can suggest something, the project had been updated several times and became a little complicated! Is it possible to make a video so you gather everything together and maybe a final clear schematic with a little explanation? And THANK YOU
HI Tom,
I plan to go back to the DC Load and produce a new schematic. I also want to cover some of the changes as a result of all the feedback. Hopefully, I will get back to it soon.
Regards,
Louis
WOW!
Sounds great! Can't wait to see that. Thanks again
I heard the Z-80 stopped production. Does that mean the ZX/Sinclair hobby scene is going to be hampered? Or has someone made an FPGA replacement of the Z-80?
😁Americans do not understand the phenomenon of this computer, ZX80_ZX81, is a simple controller for robots, available for sale since the 1980s, in the form of various kits for self-assembly. Of course, there were also the schematics and self-collection of integrated circuits. hahaha And those connecting integrated circuits with cables when there was no PCB. 🤣🤣🤣That's probably longer than the United States has been around ...
Interesting and helpful video, thanks!
Nice job but was there no option for a ZX80 case?
This is my kind of project. I'm a bit surprised you didn't mention the possibilities for those of us familiar with Z80 machine code to actually "spin" our own ROM for this project or is that a future project you have in mind?
This is probably not the best hardware to use to spin your own Z80 code, as the CPU spends most of it's time drawing the screen, which you would have to replicate. Better go for the excellent RC2104 series of kits if you want to write Z80 code.
Interesting video. I still have my fully working ZX81 (modified with internal 32K static ram which 16k are available). But the keyboard membrane is starting to show its age. Thanks for the links for ordering a new one.
BTW, the audio auto-level setting in the camera isn't performing very well. The constant limiter "pumping" effect is rather unpleasant. Maybe you could set the audio level manually ?
Thanks for your comments. I need to have a closer look at the mic I am using.
Excellent video - much appreciated - thx
Would be nice to know which lapel mic you bought please.
Excellent video and thank you. One question: As far as switching the ROM images go, wasn't there a different Ferranti PLA used in these computers or doesn't that make a difference?
The ZX81 used a Ferranti ULA to replace the glue logic used in the ZX80 (and this clone) thus reducing the chip count to the 4 ICs seen in the video. The official 8K BASIC ROM UPGRADE kit consisted of a replacement ROM, a keyboard overlay and the ZX81 programmers manual. This effectively gave the user a ZX81 without the hardware updates such as the NMI controlled slow mode or the edge connector changes needed to make it fully ZX81 compatible.
Nice job mate...
Thanks Rob
Wow Really love your work ✨✨✨👌
Nice project... Thanks
Thanks.
Very interesting! I was looking for any instructions about how to build a computer which isn't based on or descended from the IBM PC. This would involve making a custom PCB, or perhaps starting with a breadboard. Any information would be appreciated. What about a custom Z80 or 6502 computer with graphics? How did Apple and other companies make their first computers working from a garage? This project would have been much better if you hadn't used a ready made PCB, or an old ZX81 case. Why don't you show us how Soviet clones of the ZX Sinclair Spectrum were made? I've seen videos of the Kiwi computer, which is like a computer from a parallel universe, containing various chips from the 1980s and early 1990s, including an MSX2 or MSX2+ graphics chip (Yamaha V9938 or V9958), 68008 CPU, two Commodore SID chips, a custom case, and booting up using 68K BASIC or EmuTOS. Good luck with your channel, anyway!
It's really good ! Continue like this !
Thanks.
i want to know how fast is the cpu ? like the original or faster to use the basic now and not the assembly ?
I simply loved it. Thank you so much for sharing.
Links no longer exist ☹️
Anyone know where kits can be bought? Ta.
nice video very informative
Vad kul! Jag köpte en Z81 1981 eller 1982 när jag gick andra respektive tredje året på KTH. Det var början på mitt dataintresse... Kanske skall man bygga en kopia (om tiden räcker till). Jag tycker att Scullom är jätteduktig och visar helintressanta projekt där han tillverkar egna instrument med egna kretsort mm.
Thanks for your comments. My Swedish is not very good but understood what you said.
Regards,
Louis
FOR ANYONE ELSE THE TRANSLATION OF ROBERTS COMMENTS I THINK:
Good fun! I bought a ZX81 1981 or 1982 when I went to the second and third year at College. It was the beginning of my computer studies. Maybe you should build a copy (if the time is right). I enjoy your projects.
Arrg!
How you can spray a ZX81-Housing white?
I will never understand it.
;)
It actually looked good.
When I did mine, I had started with a pretty beat up ZX81 case which had marks and scratches on that made it not really suitable to be a ZX81 any more. I was able to sand off all those marks before spraying and brought it back into use. Some pictures on the original blog post: blog.tynemouthsoftware.co.uk/2017/02/minstrel-zx80-clone-issue-23-boards.html
@jorg,why not plenty of dead and dying examples of the zx81 out there, thats what i do i build bespoke units using single board computers, i build them into dead 80's machines with keyboard conversions, people seem to love them.
i do repair/upgrade original stuff too, but wont use working examples to build customs that is my only rule, if you want a pc putting in an old computer it has to be a dead example, loads of dead stuff out there cheap without killing good ones.
Ooh, I spy an NTSC enable header. Gonna get me one of these.
I would imagine the replacement keyboard is also better quality than the original since it's made by a company which makes them for scientific and medical equipment.
Yes both the Keypad and the new PCB are good quality - better than the original :) Regards, Louis
I got to mess with a Timex Sinclare when I was a kid and I will never understand the decision to use that awful keyboard...Anyway very cool project!
Thank you
Hello! What's happened with your homepage?