#vintagecomputer #zx81 #z80 Several years ago I got a wood encased Sinclair ZX81. Now I'm finally getting around to upgrading it to make it useful. Ish.
Brings back memories of my uncle who visited our house one day in '82 carrying a Timex Sinclair ZX-81, A Signetics TTL data sheet book, and a box of about 300 of the 7400 series TTL chips that were being thrown out by the company where he worked. I Wrote my first computer program on that computer. Although my uncle is no longer with us, I still have the ZX-81 that he gave to me. RIP uncle Rod.
The zx81 was my first computer, I’m from the UK and this machine was integral to making computers cheap enough for the average person to own , in the uk we had a thriving industry making games for this and the successful zx spectrum , a lot of the developers of those games are still making games to this day , we had proper keyboards for this machine it was a 40.00 uk upgrade , we loved this machine and we made it good
The video issue is due to the signal missing out the "back porch" part of signal on earlier versions of the ULA. This means that any composite monitor (and/or color TVs), cant properly determine the black level. Works fine on Black and white TVs, less so on anything else. the 2c210 ULA fixes this. There are also a few other hacks on the internet to fix it.
Just a note about this computer. Back in 1980 I was given the task of balancing the Auxiliary Air Doors on the Harrier Jump Jet. The balance weights fit into the leading edges of the doors. Their mass was a function of the contour relative to a plane parallel to the axis of the door. Their CG was the centroid of that section. I used a Sinclair ZX81 to optimize the design of those balance weights. The program took a tiny fraction of the memory available and saved me hours of hand calculations. Don't sneer at 1980's computers. Their capabilities were only limited by their users. In fact, today, I would like a computer that is as easy to program as the Sinclair.
That's an incredible story! Did you work building harriers then? I would have thought bae or whoever it was could have let you use a vax or something? Can't believe the zx81 had a part in the history of the harrier jump jet! Amazing!
BASIC command completion: the nicest experience i remember, is Benton Harbor BASIC from Heathkit on their H8, you'd type PRINT by typing PR and then the interpreter would autocomplete "INT (space)" -that had such a nice feel.
One thing that I really appreciated about the ZX81 was the single key basic command entry. The system was intelligent enough to know when to expect a command and when to expect an argument.
The machine is British, and we pronounce "composite" the way you do, so in fact for the purposes of this video you were right the first time 😉 BTW I might be wrong but I thought it was possible to upgrade the '81 to 32K internally...
Late to the party, but I wanted to say that DK on the keyboard pcb is almost certainly DK'Tronics. They made a lot of the aftermarket Spectrum keyboards and other interfaces for the U.K. market.
Speaking of David Ahl’s book(s) of BASIC programs, most of those used the ‘:’ colon statement continuation character, which the ZX/81 and TS-1000 BASIC sadly lacked. But this little machine really captured me and I learned all about it through various Z-80 books. Thanks for a great trip down memory lane. Very jealous of your real keyboard and near-mint in box Memopak 16K.
That is one sweet case. I'd have definitely grabbed it for 30 too. I especially like the supports in the case for the zx81. It was a lot less modded than I expected.
It's really easy to sneer at a machine like this in 2020, but one has to admire what Sir Clive Sinclair managed to make commercially viable for < $100 in the early 80s. Anyone that's ever bought a cheap computer owes something to this unit. The Timex variant was the first computer I technically "used" (as a toddler, pretending I was "typing"). Since all your ICs are socketed on that board, why not simply replace the SRAM with 16/32K unit? It would have been criminally expensive in 1982, but can be had for a couple bucks on eBay these days.
Not all of the Timex units had socketed chips, neither of mine do. Then, as with now, "Cheap" does not mean "Good" nor "Useful." In 1982, Commodore was running a trade in campaign promising $100 trade in on any competitor's computer towards a C64 - Almost 60% of the Sinclair's sales in the US during that time were thanks only to Commodore paying double what the machine cost new in trade in. The real hero of the cheap computer story has always been Commodore - The C64 was priced down to
I’m a 70s kid and having one of these with a tape recorder and a black and white TV in my bedroom was magical , I programmed so many silly little things on it , I had a database program of all my school friends on it , plus my own personal diary on data tape , it was so cool to own a real computer in the UK
I still have my ZX-81... Bought it new with the help of my grandparents in 1982. Whoever it was that assembled it signed the voltage regulator heat sink... On Christmas day, 1981.
Ah, I LOVED my ZX81. I originally had the 1K version with 16K RAM pack and then a friend gave me his ZX81 in a DK'Tronics external keyboard case with the 16K RAM built in (no more wobble). I also was given a case of cassettes with games and utilities. It was a joy to use. :) x
Nice buy, an interesting case! It is nice to hear someone from North America who understands why the ZX80 and zx81 were the way they were, rather than just hating on them. Affordability pure and simple. If it was a case of poor keyboard and strange video, or absolutely no computer at all, then millions chose to suck it up and buy one. Having missed out on them first time around, but recently viewed a couple of the old sinclair magazines online, I was astounded to see all of the add ons and even business software that could be bought for them. These seemingly insignificant computers kickstarted a whole industry. The zx81 was built by Timex in Scotland and apparently they were imported to USA as zx81s before Timex got the deal to rebrand them. You got there first but I was going to suggest the memotech memory pack. I wonder why other companies didn't choose that plan form as it seems much more stable than the usual memory packs.
Your "Composite" comments brought back a memory. I worked at a large computer manufacturer about 1995 doing tech support. The new line of desktop computers had a modem that was also a fax, telephone and answering machine. In Windows device manager there was a component called "telephony" device. It was pronounced 'tel if fen i'. Unfortunately we had a habit of calling it 'Tele phoney' since it was problematic and was a pain to support. When I was talking to the customer and always paused before saying the name of the device to prevent a Freudian slip.
The mission was price point. Sinclair brought to market the first sub £100 computer, in the time period you refer to, the average wage per week was about $46 (equivalent) per week or (£23), if you had a technical job, you'd earn more than that but not much more. So when you had commodore computers at £500 only those with saving power or very high paid jobs could afford them.
COMposite is a noun, comPOSite is a verb - if you comPOSite two images together you end up with a COMposite image - so when it comes to the video signal it should be COMposite.
The keyboard was made by DK Tronics UK. They sold aftermarket keyboard kits for the zx81, I myself built one for my computer when I was a 12 year old enthusiast.
Yes, usually came with a black plastic box, got one for mine. Can't remember they sold the keyboard bare though, always seen it as a kit with the replacement housing.
I can vaguely remember visiting my aunt (an actual rocket scientist) in the early eighties and she proudly showed me her Timex Sinclair running her FORTRAN program analyzing rocket test data, as limited as these early home/hobbyist computers were it's hard to understand now just how revolutionary they were
Back in the early 1990's someone passed along to me a box of three ZX-81/TS1000s (I forget what the mix was) that they were given when they mentioned they'd like a computer at home. (In exchange/out of pity I gave them an IBM XT I got at a government surplus sale for about $20.) The only good use I ever found for one was stealing the Z80A CPU out of it to repair a TRS-80. (I did manage at least to get one of them to "work", despite all three having completely shot keyboard membranes. Had one memory expansion pack between them that would crash the machine if the connection was stressed *at all*, and this ridiculous cash register printer thing.)
I have a pile of them myself. Bil Herd of Commodore fame said in a video they used to use these machines as doorstops. I just remember being curious about them.. you'd see them at most computer shops tucked away in a corner. That said, I've seen some of the high res stuff they can do with mods and it's pretty impressive. But that keyboard.. uggggh
I just found your channel last night, and hands down you’re now my #1 non-gaming channel. About time one of you old computer guys with a seriously historic collection started showing that stuff off on YT 👍
It's all about patience and tons and tons of searching. And some luck. I look at ebay every day and every now and then a deal like this comes up and I leap on it.
Interesting ZX81. You should try some of the 16K High Res games, like Manic Minor, Space invaders and so on. Pretty impressive for back in the day on the ZX81.
Someone was a master cabinet maker. Looks like what my dad would make if I had told him I needed a computer case. You can probably fit the expansion pack by taking it out of it's plastic cartridge.. or if you don't want to do that.. using a male to female extension ribbon cable.
Nice video! Re the single key entry - I think most BASICs do tokenisation, i.e. store the commands as single bytes as lines are typed in. Getting the user to do it by using the single key entry meant Sinclair BASIC didn't need to include tokenisation code therefore it fitted in the tiny 8K of ROM. They sold it as a time saving feature but when the Spectrum came out it had so many commands that some of them took more keypresses that actually just typing them.
I loved my Timex Sinclair 1000. I rarely used it for games. I bought the tape programs and reverse engineered them to understand hoe code was written and then wrote a lot of code to practice and learn. I enjoyed writing trigonometric calculation programs. I always wanted to use the board edge connector for home monitoring and relay control.
Super interesting find, amazing what gets done to these machines. BTW, good to hear Composite being said properly, I'd do the drinking game in reverse :-)
I feel like it's being "Said platform-appropriately." During the "Zee-80" project i noticed it was all kum-PAH-zit. During the "Zed-Ex" project, it's KAHMP-uh-zit. He's just matching the talk to the tech. My Chevy has a trunk. My MG, has a boot.
Not sure if someone else already said, but old cassette units offered "remote control" that was just a remote pause switch: you could pause or release playback or record. Can imagine he wanted to control tape from keyboard
I had an Atari 400 with it's membrane keyboard. I had to put a replacement B-Key keyboard from a third party supplier and a memory expansion to 48K before I was happy to use the computer on a daily basis. It made a huge difference.
@@TechTimeTraveller Ahhh, that's actually pretty smart, honestly. If it were me, I'd have lost the original case years ago and by now would probably feel pretty sad about it haha
That is a geogoeus looking case. There is a very simple composite mod using a 555 IC and a couple of transistors that gives a perfect picture by adding the back porch to the video signal. (Which the ZX81 is missing.). Also you can replace the built in 1K memory chip with a 16K or even a 32K chip. It's a bit tricky, but worth it. :)
It was not meant to be typed on , it was a keyboard with basic command shortcuts on every key , very quick to program in basic on that little 49.00 uk machine
No idea why the guy that made this kept the ZX81 PCB inside the case, makes no sense. Would be much easier to just mount the bare board under the keyboard.
Bit late to the party here, but hey... you're a time traveller. All the while you were complaining about the height of the Sinclair 16K board I was yelling, “You need a Memotech!”. They made some great ZX81 stuff. I had (have) two piggybacked 16K packs and a keyboard, which connects via another “cartridge” and had its own aluminium case, similar in construction to the RAM packs, with proper custom-made keycaps. The only drawback was that it followed the ZX81 layout precisely, with a space key instead of a bar. Otherwise it was actually one of the best keyboards I've ever used (although, as you've noticed, the ZX81's keyboard response was never very good at the best of times). And I say “COM-posite” too.
Timex factory in Dundee was where the ZX81 (and ZX Spectrum) manufacturing was outsourced to. That's presumably where the link between Timex and Sinclair came from. Bought a similar idea 3rd party keyboard and plastic case for ZX Spectrum from DK Tronics back in the day. The Spectrum original rubber keyboard was better than the ZX81 but still terrible. Atari 400 had a similar membrane keyboard but without all the shortcuts.
You can put 16kb on the ZX81 motherboard by replacing the 1kb with 16 and adding additional addressing lines. Very simple procedure and no memory pack needed!!!
A friend of mine had one adapted to kinda hi res graphics.... the only way to do it is a mod that switches the character map out of ROM into RAM then you can program your own characters to get a hi res "feel".
Nope, most high res drivers simply used single rows of the 8x8 characters individually, and used a bit-pattern that was nearest to what the high-res graphics demanded, the character set was NOT normally moved to RAM, although that was probably possible too, but took more RAM. In bothy cases the original display driver had to be replaced.
All BASICS store the commands as "complete commands": they are called tokens. What is different on ZX's is that the keys emit directly those codes, so the keyboard buffer don't need to be tokenized by a routine. This routine can occupy a relatively large amount of ROM. So this is made to save ROM space not RAM.
So my previous comment seems to have vanished. If this was due to a YT 'glitch' and you would be interested in my re-cased 81 then let me know and I'll repost the details. To summarize the earlier post, a great video with some excellent comments. Kudos on your game playing skills, especially one-handed! You got further than I normally did with two lol. Your pronunciation efforts were praiseworthy except for MK14. The letters M and K are pronounced 'em kay' since they stand for Microcomputer Kit (with 14 main ICs) and are not an abbreviation for mark.
Holy crap a keyboard you can ACTUALLY type on! Beauty of a wooden case as well, someone worked really hard on that. I guess they were trying to make up the difference to a VIC-20 they could have spent the same amount of money on. Hilarious how they mounted it, didn't even take the board out! I bet the "TP" key connected to the phono jack is because some tape decks had the ability to automatically play/pause from a remote source. Maybe he had wired it in like this so he didn't have to reach over? Tape play/Tape pause? Lots of people joke about how badly British cars were built, but we always used to joke that most weren't built at all! Simply put, the fall of the British automotive industry in the 1970s and 1980s and the massive economic downturn immediately after falls solely onto the squares of the people who didn't want to work anymore.
The amazing thing is, for all that it may look like a toy, it actually IS a computer. I don't know that the wooden boi looks *better* than the ZX81. They're both kind of appealing in different ways. The original ZX81 looks like a sci-fi prop. The aesthetic appeal of woody is obvious, though. 8:57 It's possible to upgrade the RAM on the main system board, you don't nessicarily need the ram pack. ( ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-14eL_oWhhXo.html ) 19:00 I wonder if that was used as a means of fast entry? Rather than load and save binaries, just dump text files via serial and as far as the 81 is concerned it's being typed?
TP is probably for the remote play trigger on a cassette recorder. "Tape Play". Normally would go to a foot pedal or something for an interview style recorder
The Timex Sinclair 1000 was an 80s computer, not a 70s computer. I can still remember as a kid all the hubbub about a new 50 Dollar computer. But then, right after the price came the specifications. That's when you knew... It was just junk. I had just bought my vic 20. Then my mother was like "hey, they have a new computer for 50 bucks" and I was like, sure am glad I didn't buy that junky thing.
Helps if you hold the keys down in 3D Monster Maze rather than tapping them. ZX81 was my first computer... I remember the long load times. Almost as long as waiting for something to load from disk on a C64....
12:48 Interesting, in the UK your pronunciation of composite would be correct :) I believe technically this would be correct, as the version you're trying to replace your prior pronunciation with would be a verb, you composite(your new version) things together to get a composite(your original version)
I think it gets confusing as a Canadian because we take our cues both from the UK as well as the US. I've always said 'com-po-zit' rather than 'compoz-it'. And I got corrected a lot on that by American friends. When in doubt I suppose I should go with the inventors of the language.. :)
In the UK it was always ZX for left and right and something like '/ for UP down. I hated games that used ASWD or similar. But its what you're used to...
I had one and my upgrade was similar but used metal not wood to mount the aftermarket keyboard. Plus also did the mod for composite video and used a green screen monitor. The issue was adding the correct capacitor value to the mod; without it yes, the brightness would be too low. Ultimately the big issue that caused me to move on was the lack of a proper printer
(if already said or proved wrong later in video please disregard thiis comment.) 17:14 may be a method of saving and loading programs via saving the signal of each keypress and then allowing the to be played back. To test this you could plug in the tape recorder start the recording type a short message stop recording rewind yhe tape and then power cycle the computer and hit play to see if it works
29:56 The new plugs you have are stereo. You need mono plugs. Looke at the bands on the plugs. The new ones are double pole. The old ones are single pole. 30:07 - Now those are both single pole mono jacks.
Good grief... I can actually remember that " TO " is shift-4... I haven't touched a ZX81 since 1982 and I still remember that..... younger me really did need to get a life.
Zx81 looks like proper computer in that case Sinclair misssd a trick , how much more plastic would it have taken to make it a full sized case / keyboard . Sir Clive Sinclair was my hero in the 1980’s
The keyboard is a dktronics unit, must be a really early one those were kits,the more common unit is a whole case/keyboard, that came prebuilt you just removed the mainboard of the 80/81 fitted it in the dktronics case and plugged in the keyboard. the biggest single rampak for the zx80/81 is 96K.
I really can't say.. I thought it odd too.. I think the case has some kind of ground metal or such in it..maybe they didn't want to bother with that. Or they just didn't want to toss the case.
Whether they knew it or not, it was the right thing to do. It preserved the RF shielding. Technically it was illegal to use without proper shielding, and practically not a kind thing to do if there were other radio spectrum users nearby. Those old PCB layouts and associated cabling were notorious radiators. Imagine putting together a ZX81 clone using surface mount chips and a ULA analogue with discrete logic, using a 4-layer PCB and modern techniques. It wouldn’t need any shielding and remain compliant. Of course back in the 80s such work was the domain of military and professional gear and out of reach of consumers.
@@absurdengineering Yeah that sort of makes sense to me. I wondered if the shielding had something to do with it. You wouldn't just leave the whole thing together like that unless you had a good reason. Many thanks for that insight!
that thing is great! Maybe somebody has thought of this already, but I wonder if the key wired to the RCA jack was for a "remote" control for the tape recorder. Although having a momentary contact switch for that would be annoying. Was it a locking switch?
As someone who has had personal experience with this model of add-on keyboard, I can confidently say that none of the keys were latching, thus using one of the six spare keys for controlling the tape recorder remotely would indeed require the user to hold down that key for the duration of the save/load process. I am just as baffled as you and Brad are regarding this key.
wonder what the rational of keeping the stock case in the box, there's oodles of room if they had just secured the board to the box with a few stand off's (back in them days I would just use hex nuts large enough to pass the screw into the wood but not too big to short... many wooden box radio shack projects when I was a kid)
DK'tronics (yes the apostrophe is compulsory) made early Spectrum and ZX81 keyboards. Yours doesn't match anything I can find on the net, but that doesn't mean they didn't make it. They apparently didn't mark their product except on the PCB, so there y'go. I dunno about spending so much money on a full keyboard for the ZX81... it's sort of like throwing good money after bad. The ZX81 is a great thing for what it is but it's cheapness is absolutely in it's genes, pretty much every design decision, including the ingenious ones, seem to be in the name of saving money. To get computers into the hands of people who couldn't otherwise have one. I think if it were me back in the day, were I old enough, and I'd bought this keyboard for my ZX81, I'd just end up feeling cheated, like, "what am I going to do about the barely-existent monochrome graphics and no sound?". The keyboard's too good for it! Hey, silly question, because of COURSE you did, but did you ever play 3D Monster Maze? It's like Doom, man, with a Tyrannosaurus Rex!
just replace the onboard 2k SRAM with a 32k SRAM chip, there are loads of instructions on how to do that. you're nuking the problem when the answer is so simple.
This ZX81 has 1k the chips in positions IC4a and IC4b being 2114s which are 4 bits wide. A 2k version would have a single 2016 fitted in the IC4 position.
Not those that were sold in the UK and Europe, but there was a brief period when the ZX81 was exported from England to the USA; these machines had to have the FCC approval sticker, of course. Soon, however, Sinclair struck a deal with Timex* that allowed Timex to manufacture and sell the machines in North America under the Timex-Sinclair brand. The TS1000 was followed by the TS1500, which was a modified ZX81 with 16K of memory onboard, and a redesigned ULA; this model was housed in a case that resembled the case for the ZX Spectrum, with the same kind of rubber keys as the Speccy as well. The last model produced by Timex-Sinclair was the TS2068 which was an enhanced ZX Spectrum: it had a slot for ROM cartridges which eliminated tape loading (and all the problems _that_ entailed), a built-in 3-voice sound generator (an AY-3-8912), two joystick ports, and some new screen modes with up to 80 or 85 characters per line and a higher colour resolution (8x1 pixels instead of the 8x8 pixel colour blocks of the Speccy). Unfortunately, these new screen modes meant that many games were not compatible with this machine, so Timex-Sinclair also had to release an "emulation" cartridge which contained an unmodified ZX Spectrum ROM. *At that point, Sinclair had already been using Timex as a manufacturer for the domestic models, which were made in a factory in Dundee, Scotland.
