Hi, I'm the designer of the 3d printed case you showed at the end. I wasn't sure anyone would be interested when I first made it, but it seems the ZX81 fan base is much larger than I expected.

Such a magical machine. It looks so uninspiring, but when I was 12 years old this was my first computer, and absorbed my life when I first got it. I learnt to code on it and went on to make it my career. I've written code in C, COBOL, Java, Ruby, JavaScript, Python, and Kotlin, but nothing I've done has given me the same thrill as going through the first few example programs in the excellent ZX81 manual.

This was my first computer. My highschool formed a computer club and we ordered about 20 of the kits. We waited months for the kits to arrive. On the day that the kits arrived I had to work after school until to 9:00 PM. I started my build when I arrived home and completed my build by about 2 AM. When testing I had an issue where the screen image would role every second or two. I took my completed kit to school the next day and I popped in to see my Physics instructor who was the club sponsor. I mentioned that I was having an issue with my computer. He reached out and put his hand on shoulder and in a condescending manner said, "It's a kit that you need to assemble before it will work". When I explained that I had completed the kit yet still had a problem he was shocked and agreed to look into the issue. Luckily he found the cold solder connection that I had missed. The next person in my club to complete the build was 20 days later. This kit started my career.

This is a trip to memory lane! The ZX81 was the first computer in my family, my brother (who is a geek) bought it and I especially remember the frustration when the 16Kb expension lost connection when it moved just a little bit. All lost and start over again... great memories about programming though

Wow! Thanks. I am martin de jong A.K.A. Mahjongg the designer of this clone, and I started this design 38 years after 1981, hence the name ZX81+38! However due to Covid I was unable to finish it until now, although early adopters helped me to fix a few bugs, my revision 1.9 is now fully working. AFAIK you are the first to put a video about my clone on KZfaq! That is great! This is my second ZX-81 clone, the first one (the ZX81+35) used SMT (surface mount) components, but because I got feedback that my clone was great but that SMT was "a bridge too far" for most hobbyists I designed this second one. During my previous effort I fixed all problems with my "ULA replacement logic" and it is now as perfectly compatible as I can make it, and everything I have thrown at it (various highness graphics versions etc) all work, and obviously I fixed the "front port bug" that earlier ULA's had. My replacement logic works with modern TV's, and if you have a CRT it even displays the famous loading bars of the ZX-81, because I did some trickery. Newer TV's just switch to black if they loose the sync signals. I see you are using the keyboard without the paper overlay I have designed. You can download the .PDF of my overlay and print it out (it should be correct to size for my keyboard), it has holes for the key stems to poke through, and all the texts are arranged around them. As you might have seen, not only can you get the Gerber/drill files for a PCB manufacturer, but also a complete BOM with exact order codes for Farnell, Mouser and Reichelt, and I made a drawing showing where all the different components go. Obviously there are schematic's and even the CAD Files (for KiCad 6). Modern 27C256 eprom no longer have the glass window, but are sold as "OTP's" (one time programmables) for much less money. My clone supports 27Cxx type (E)PROMs, but also (with a few patch wire jumpers) 28c512 (EEPROM's), the W27C256 from windex which is electrically erasable (fully 27C256 pin compatible) and even the original ZX-81 ROM. And by the way it has 16K RAM built in! (or 32K if you want that). I know that 27C256 ROMs are affected by the Chip-crisis, but you can still buy an 8K EEPROM (a 28C64) from Reichelt for about ten euro! Just change JP10 so that pin 27 (nWR for this EEPROM) is tied high. If you need support you can mail me at mahjongg AT xs4all.nl. on my maker-space www.revspace.nl , Where I kept an extensive journal about the design process of the ZX81+38 in the projects section. I have just uploaded my take on the cassette replacement unit known as TZXDuino (aka Casino) a minimalistic version without display and with just two buttons instead of five, it was specially designed to build into a sinclair spectrum 48K for a museum I work for, but should work with my ZX81+38 clone too. I'm also planning to release a programmable sound generator (software compatible with the ZON PSG), but my version uses the GPIO port of the PSG Chip (a AY-3-8912) to control (bitbang) an SPI interface, used to connect a SD-Card reader. A german fan has written menu driven software for it which can be placed in the unused second 8K section of the BASIC ROM. he said you can download ".ROM" games (etc) with ten times the speed of a cassette. (a working version already exists for my older clone ZX81+35). This new version will be compatible with ZX-81's and my ZX81+38 clone. Note that I am a moderator on the raspberry PI forum, and I made a thread about my hardware designs, where you can directly comment me its in the "offtopic" section.

In high school, I took a vocational computer course (3 periods a day for 2 years) in which we used a PDP-8e. I wanted to buy a computer once I graduated and the only thing I could afford was a ZX81 (not a T/S 1000 as most Americans have). So I ordered it as a fully built machine with the 16k RAM pack. The first computer that I actually owned. I used it to it's utmost for a year or so (velcro used to keep the RAM pack connection in place). I think the only commercial software I got for it was Flight Simulator from Timex/Sinclair. But I must have written 100 or so games and application software for it in BASIC. I always thought the ZX81 or the T/S 1000 BASIC language was quite powerful for it's day. It had various commands and statements that weren't even included in the DEC PDP-8e BASIC that I was taught in school.

I still have my ZX81. 😀 I learned to program on it when I was seven or so. Love it to bits, this is really nostalgic for me.

Nicely done! I understand the interest in the ZX-81, as it was the first computer I could afford to buy, and it still has its own special charm today. It was a machine that encouraged tinkering, and tinker a lot of us did. Thanks for the memories (cue Bob Hope).😀

The original ZX81 keyboard was ridiculed for its flatness, lack of feedback, etc. Now we have gui interfaces which no longer have buttons that look like buttons but just flat bits of coloured screen - the "modern minimalist look"...very much in the style of the original ZX81 keyboard. Tge ZX81 keyboard was clearly so ahead of it's time...

Outstanding. As a child of the 1970s I cut my teeth on the ZX81. When you started test program at line 1, I could hear myself screaming..NOOO....lol

Had one. Learned Basic with it. Had the Ram Pack 16K and the thermo printer, I used to print off Menus for Hotels way back they thought it was DA BOMB. !!! hahah.

Fascinating video - thanks! It would have been interesting to have a commentary during the build telling us what's going in and why, to describe more about how this recreation was designed and produced.

I'm deeply impressed of your speed soldering and assembly of the ZX81

I learned Basic on a Sinclair ZX81. I had the memory expansion and a printer!!!!

Thing is, back in the day with the ZX80 and ZX81's was after a good while of use you had a series of burnouts on components so by and large they ended up partially all new under the hood because of the incessant heat death of the bloody machines which the Spectrum never suffered from. I remember WWIII over my ZX80 scorching my new bedroom carpet, that thing melted and burned out almost daily and the plastic on the expansion pack often turned brown and sagged weirdly. We were lucky in up the road from us there was an early RS Components shop and he was always able to get in bits and pieces fairly quick and the shop owner was a Sinclair nut too so helpful in keeping these ticking time bombs from blowing up :D

I have bought a timex-sinlair-zx81 on 09 of August 1984. It had a price of 49 Deutschmark. On the next day i had a motorcycle-accident driving from my job to home. I had a kidney-rupture and stayed in hospital for about six weeks. My oder brother found this ZX81 at home and bought a thing for it, it was called "Azmic-ROM". It was a total change of the system, no more basic, only Z80-Assembler. I knewd the mnemonics of 8080 and Z80 cause we had a self-constructed comp at home, so i wasable to write asselmbler-programs in my clinic-bed, the little ZX on a plasic-bench on my bed. Later i wrote "Wurmi" on my Oric Atmos, that i had bough some month befoe the accident happened....

And without a wodge of Blu Tack to deal with the RAM pack wobble!

A friend of mine still has his Spectrum 128k with all the accessories it originally came with, housed in its original box in his mum and dad's loft. I'm just waiting until they go on holiday........

My first computer...crap by todays standard but loved it

This brings back memories! I built the ZX81 kit version when it was made available. My first computer and a lot of fun 🙂

Brilliant!! This was my first personal computer. The experience of programming the ZX81 Basic was much more fun than programming COBOL on a mainframe. The iconic design of the machine and the keyboard still seem second to none in my opinion.

Next up would be a new incarnation of the Swedish ABC80 computer. It was more competent but used a Z80A processor at 3MHz with 16k ROM and 16k RAM.

Reminds me of way back in the 80's we found a source of ULA chips for the Spectrum so managed to make a working unit. We hand-wired it on a patch card and used a mechanical keyboard rather than a membane. It was great playing those old games with it like Attic Attack amongst many others.

Brings back memories, my friend Seth and his dad had a ZX 81 he assembled , since I was in the states the next year my mom and stepdad bought me a Timex Sinclair 1000 , I eventually got a 16k pack. Then I enjoyed the true frustration of looking hours of work and data because of my heavy fingered input and a battery pack that had slowly walked its way out. Good days.

In principle you could recreate the ULA with an FPGA, then you would be with the original ZX81. So it is a ZX80 with NMI extension, which is also much easier to implement and is still timeperiod correctly (there was an extension for the ZX 80)

I remember a teacher at primary school got hold of a ZX80 and and ZX81. It was a thing of wonder and started a lifelong interest in technology and computers. A year later we got a ZX Spectrum 16k at school still remember the excitement now.

I appreciate your historical accuracy I wouldn't have faulted you if you had hardwared around the 16 bit addressing.

Well clearly without the original keyboard and case being 100% identical it's just the naff motherboard you've recreated ;)

I love how u have ur hands in time with the music nice wee touch ❤️😁😁

These screen tearing artifacts are caused by poor voltage filtering by the 5V regulator (LM7805) which is overheating. I removed them by unwinding 10 turns of the secondary winding of the transformer in the power supply from the transformer. It is also good to replace the heat sink plate with a larger one and stick the heat sink on the ULA. After such a modification, my ZX81 has been working flawlessly for years. Te artefakty szarpiące ekran są spowodowane złym filtrowaniem napięcia przez stabilizator 5V (LM7805), który się przegrzewa. Ja usunąłem je poprzez odwinięcie z transformatora 10 zwojów uzwojenia wtórnego transformatora w zasilaczu. Dobrze jest też wymienić blaszkę radiatora na większą oraz nakleić na ULA radiatorek. Po takiej przeróbce Mój ZX81 działa od lat bez zarzutu. Greetings from Poland - the most free and beautiful country in the world

I've been playing with computers for 40 years and made a very successful career as a software engineer and it all started with a ZX81

That sure brings back memories. I mail ordered a timex sinclair 1000 in the early 80's from England and it was my first computer. I loved that thing. edit: I had it in my head it was 4k without the memory pack (which loved to shift and reset the computer). I also had the thermal printer with those long paper strips it produced. I only owned 1 game, a flight sim. But I wrote so many games with it and learned basic from it.

That's awesome, though a ZX81 built from discrete components instead of a ULA sounds more like a ZX80 to me!

Great video! Maybe it IS now time to finally solder the ZX81 DIY Kit I stil have in my basement ...

My very first computer, I'll always remember the first time I tuned my TV to channel 36 UHF and saw the magic cursor.

Wunderbar peoples who posted here. I'm also a Z80-holic. 🙋‍♂️ 👍 Thanks for the video, you are goood!

I'm in.! Have a grandchild to lookafter and 347 other jobs i'm avoiding but I think this one can jump the Q. Top Banana.! Thanks

Great project and video 👏, but who else is triggered by line numbers 1 and 2 instead of 10 and 20? 😁

Very cool indeed!

A ZX81 made with TTL logic instead of an ULA , that could be the Brazilian made TK83. That thing heated a lot and had some rare compatibility issues with software that pushed the limits. Anyway, well done! This machine put me and many others into computers back in 1982

Great in it's day, but that day has gone, let it rest in peace...............

Awesome the ZX81 was my first computer as a kid, remember going into Debenhams with my dad to get one, we went back a few weeks latter to get the 16K RAM pack. Happy days, I latter went to VIC20 (didnt like much) then moved to Atari 600XL and never looked back.... going on to own every Atari made, then I moved to Psions before ending up with Mac

cool project! - the ZX81 was my very first computer, and i didn't even remember what happened to it...

I still have a couple of ZX81's somewhere in the garage, along with power supplies, 16k memory units and various interface boards I built back in the early 1980's. Maybe I should get them out and put them up on Ebay, I never imagined people would still be interested in them.

Great video. My ZX81 still works, I have the 32K RAM pack, and printer. I have a small LCD monitor that accepts RF TV channel 2 NTSC.

For the Dogsbody (ULA) - at least the digital parts of it, I would use a decent Xilinx FPGA with lots of CLBs and routing. I would clock it at the same speed as the Z80 (or maybe faster). This way I could code it to do exactly the same functions. A lot easier than a bunch of discrete logic and it can be changed as needed. It could also be possible to have added features - like an interface to use a PC as an In Circuit Emulator for the Z80 CPU. In fact, the ZX81's RAM, ROM, and even the Z80 CPU itself could all be implemented in a single massive FPGA with today's technology. The heart of the ULA was (along withe some "glue" logic) effectively a interrupt driven DMA from from RAM (the characters on the screen), and ROM (the 5x7 bit patterns for each character pattern) directly into the ULA so the bit patterns could be shifted out to the TV Modulator. I would use a fully digital FPGA with 3 video output signals to generate NTSC (or whatever): 1 for Sync (Blacker than Black), 1 for the Sync Porches (Pluge), and 1 for pixel Off (Black)/On (White) level. So a simple analog circuit would be used to generate those levels in real time from the FPGA to the Modulator. So: 1 FPGA, 1 High Speed Analog Video Ciruit, an RF Modulator, a Keyboard, and a Power Supply. I might even be able to make the Screen RAM portion dual port so the CPU can run in Fast Mode but display video at the same. To see screen video while running, the ZX81 had to "steal" code processing time during the video Syncs (Slow Mode) - the result: The code/editing "appeared" to run in real time with constant video, but since the RAM was not dual ported in the ZX81 (to keep it low cost) the BASIC code ran much slower in that mode. The Whole thing would be roughly 1/5 the size of the ZX81.

You need the shoutout to the PCB maker, of course, but you can make something like the ZX81 or replicate it on a breadboard even today. At the clock speeds you can get away with nearly everything. It's also amazing how many PDIP logic ICs you can still order today.

Great effort. Looks great 👍

Just fantastic ! You made my day with this video Thanks

IIRC, I used to have the schematic for the ZX-80. I don't remember the differences between the 80 and 81. IIRC, the 80 used standard parts so it could be used as a guide to avoiding the need for the ULA in an 81 recreation.

I've still got my zx81. With printer and 16K module.

Wow, i begin programing with that kind "computer", very good memory in my head. My fist software was "PacMan Game". Thanks

i have my original zx81, printer and ram pack still working when i last tried it trying to find games in mp3 format to replace the tape machine

Tip: you don't have to type a space after the line number. 😀

To be true, I'd use a bit of flux and a soldering paste. Insert few components and just use a hot air :D. But, if you enjoy that, I see why not. I've got too many electronics repairs to spend so much time on hobby :).

That was my first computer 1980

Superb. Subbed. I really could see a market for pre-built ones, especially with keycaps with all the keywords etc. Reminds me of the Soviet clones.

looking forward to ep2!

My very first computer was the ZX81and was in kit form, it took me about an hour to build it worked. Over time i expanded it and even made my own keyboard and made a wooden case to put it all in.

I remember launch RRP as £79.99 oddly

I'm working with mainframes now, but I missing my ZX Spectrum...

Technically specs were somewhat lacking for 1981.

I was yong when i work with this computer ( basic language..)

Subscribed. This is for the algorithm.

Famtastic

I had a 16k memory pack on the back lol 😆

I wouldn't mind running a Raspberry Pi on a Sinclair case with a traditional keyboard (no chicklet or membrane keys).

I moved my ZX81 into a proper case with a clicky keyboard and wired the 16K rampack to the extension port with a ribbon cable. There was a circuit called "High Resolution Graphics"(HRG) published in one of the Sinclair magazines which allowed you to switch the 1kRAM into the ROM address space for the character set, giving 16 8x8 sprites. Have you considered replacing the 1K Ram with a bigger one up to 64K?

it must have been a great children gift to have fun soldering it altogether during the xmas break :D

One other design you could have possibly tried if you couldn't get that PCB is to clone a ZX80. I had one of these (as well as pretty much all the other Sinclair machines up to the Spectrum+) and essentially hardware wise they're very similar to the point that the ZX80 will run the ZX81 ROM pretty much flawlessly with the exception of SLOW mode, which the ZX80 hardware didn't natively support, thus making almost all ZX81 games unplayable! THE ZX80 is almost the the same as a ZX81 but with no ULA chip - made from discrete off-the-shelf components, hence many more chips and components on the PCB (and at the time more expensive). At one point a company did come out with a kit to provide SLOW mode on the ROM upgraded ZX80 which I bought - however my soldering skills were never very good and I managed to destroy my ZX80 when some solder crept under a chip and shorted out a circuit. Shame really, as a working ZX80 is now worth a fair few quid. Mine did also overheat (from the beginning) and this caused it to switch from 50Hz to 60Hz display (or jump and flicker between them for no reason) - not a big deal as my b&w telly coped with both frequencies. Someone also came up with a software only SLOW mode for the ZX80 (running the 4K ZX80 ROM) to prevent screen flicker - however that didn't work on the ZX81 SLOW setting and was intended for custom made machine code software for the ZX80 (of which there was very little available indeed!). I wouldn't be too surprised if that board you bought was heavily based on the ZX80's architecture. Incidentally, if you can get a ZX80 ROM image - this runs on a ZX81 too. One other interesting fact - all the Sinclair products were completely unshielded. Not generally a problem but at the time I was also into CB radio (the original legal version in the UK) and keying up a CB transmitter anywhere near the computer would cause it to go crazy and usually completely crash or reset, and that was just 4 watts of TX power! These days I use a laptop right next to my 400 watt ham radio transmitter - no problems ever encountered!

Great video im a subscriber now. Where can i get that grey desk mat with the small "pockets" that is used when soldering? Good work, thanks.

A hello world example using line numbers 1 and 2 instead of 10 and 20? Controversial! 🙂

Interesting channel 👍👌

it was my first PC !

USB-B port for power? What a monster.

So does this new version show the loading lines on composite display? Thanks

👏👏👍

Around 12, or so, years ago I purchased a number of ORIGIONAL new old stock ZX81 kits from “zebrasystems”, I’ve yet to build any of them & would NOT use the included electrolytic capacitors in the original, now, nearly 40 year old kits, just replace them with fresh new caps. The ULA is the only custom IC in the ZX81 which can be reimplemented & replaced with 74xx series logic.

My first computer, with 16kb expansion 😮

ULA can be substituted with FPGA if you want it to be just like its original counterpart. The best part is that ancient 8-bit CPUs are still made so you can hop onto Digi-key and buy either 6502 and Z80 or both today, this kind of stuff is popular with hardware hackers who want to roll their own computers if they want it simple, before even graduating to 68k or x86 processors, something like that.

This looks like fun... Exactly what files do I need to send to pcbway? so I can give it a try?

Do NOT need to build a new one!!!!!!!! I have 3 or 4 of the original Timex-Sinclair's sitting around here somewhere!!!!!!!

Very interesting, thanks for sharing. 1 question if I may, why is it necessary to fill the eeprom with duplicated content? Or did I misunderstand?

Excellent! Did I miss a part where you spoke about sourcing parts? Has anyone done a video on JCWolfram's AX81, a ZX81 on an Atmega?

Q: at 1:25 does that mean you're actually building a replica ZX80? That had a series of logic chips replaced by the ULA.

This with a Forth ROM?

Not to be rude, but why is the question today "Can you build a ZX81" ... Why isn't it "How much Computer-Fun can you make for 69 money (or 290 money) today"? Seems to me like that would be a better use of clearly rather capable electronics designers/wizards.

i still have this computer i lost the 16k adapter

Why? When an appropriately-sized right triangle of wood could stop a door just as well? ;)

Can I use it for a device controller?

Brilliant! I would love to do this. What was the total cost of all the parts?

Interesting build. I’ve just sent for a zx81 from an eBay seller sold as untested! At worst I’ll have a case for an emulator!

Is there some way we're supposed to somehow hang on and cope in any way before Part Two of this? 😳

When you say "get quality pcb's" I presume you mean 'good' quality.

Also who do the music it's really gd !!❤️😁😁

If you are super lucky and have money to burn, can you sometimes still find the original new old stock zx81 kits.... but its a shame to build those up TBH.

As i rember (not pesonally) ZX-80 has discrete small chips instead of ULA nad was sold as a kit... Anyway ZX-81 was my frist *my own* computer (sigh)... circa 1988... i have one in not orginal case and "normal" keyobard and one pristine.... Many hours, days and months... manually assembling to machine code... dissasembling ROM.... and other nasty things ;)

I built mine back in the day because I was poor. Because you used a bigger eprom you could of added useful lookup tables and routines instead of repeating the zx81 rom image 4 times. Not sure how difficult it would be to allow the system to see it though

isn't it supposed to be a red sticker on the UV window on the eprom?

My question is. Where did you get the part from?