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Old 13th Mar 2021, 8:29 pm   #41
julie_m
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Default Re: Enhancing PETs and other Vintage Computers

It certainly would not be hard to use the GPIO of a Raspberry Pi to pretend to be a printer, capture the data and process it; just sending printable ASCII codes to a simple text file, or detecting the control codes to select graphics mode and building up an image file.

Python lets you create an image file as easily as populating an array with the colour values of each pixel, which you can derive from the graphics mode data.
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Old 14th Mar 2021, 12:00 am   #42
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Default Re: Enhancing PETs and other Vintage Computers

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Originally Posted by SiriusHardware View Post
Back in the day the Epson command set was king, so even other manufacturers like Brother, Panasonic, etc, could be communicated with via Epson-compatible control codes. Each printer had its own unique non-Epson codes to support its own special features but you could always do basic printing just by telling your computer that the connected printer was an Epson.
Yes, I'd forgotten that every matrix printer had an "Epson" mode. I had a Citizen MSP-80 and used Epson drivers for it.
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Old 14th Mar 2021, 12:43 am   #43
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I was posh I had a Real EPSON...
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Old 14th Mar 2021, 12:49 am   #44
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Ah, my first proper dot-matrix printer was a Panasonic KXP-1081. Quite a nice printer. To this day, I still prefer looking at my program listing on fanfold paper, it's much easier to 'scroll' straight to the bit you want than on a screen, IMO.
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Old 14th Mar 2021, 3:05 pm   #45
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I was posh I had a Real EPSON...
Although did you have to (DIP)switch it to 'IBM' mode, for use with that PC?

I recall many printers have both, and also getting the right CR+LF setting, for different systems.

I did eventually get a (used) Epson LX80, I still got (I think my School's BBC Computer room had the replacement LX86 / maybe an FX800?)

One problem I found was that not all Epson's were equal! There were FX-80 function and also (less?) RX-80 (maybe MX-80?) ones.
Many lacked the reverse-feed command, that allowed you to go back to start and manually swap the ribbon to a different colour, for budget colour printing (was rather flawed with impact printers, as it ended-up contaminating the ribbons with other colours)
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Old 14th Mar 2021, 3:28 pm   #46
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there hasn't been much coverage of ZX81's 40th
Oh, I don't know, though. Here's a little Youtube piece by our very own Timbucus:-

https://www.youtube.com/watch?v=05eR5zWI0GA

And another one by RetroGamesCollector, whose love for the little black wedge is very evident. There doesn't seem to be a version or variant he does not have in his collection.

https://www.youtube.com/watch?v=QYnMk1X8uio

Those are just two, search 'ZX81 40th' on Youtube.
Thanks for these, I've just had a brief look at and will watch later (So will get the views a bit higher than < 300 so far).
I remember the controlling a power station with a ZX81 article (Dont't knock the RAM pack!), and manufacturers making claims on what theirs could do.
And I have since acquired virtually all that's in Timbucus's one, after a friend originally had a ZX81 + Maplin I/O board back in the day, and I ended-up with his ZX81 built-kit + stuck-on plastic keyboard buttons upgrade, after he'd killed the ULA, later fixing it. Also have a dk Tronics keyboard cased one.

It seems the more main-stream media has passed this event by (Not even seen a Tweet from TNMOC / CfCH, but may TheRegister had something).

The Spectrum's 35th seemed to get a bit more publicity and I went to an event on it with someone coming from Switzerland to present some of his rare versions in a talk at CfCH (A more recent Acorn-special weekend is on Youtube). But I'd expect that the ZX81 is equally as famous (even if rather less were sold, declining back through ZX80 & MK14 making them so much more valuable)
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Old 14th Mar 2021, 3:44 pm   #47
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'81s were the first machines you could buy from a high street shop such as Menzies or WH Smith so they sold in far greater numbers than their predecessors, to the extent that it is still possible to buy an unboxed real ZX81, just the wedge, for about £10-£20. You can expect that you will also need to replace the keyboard membrane (~£15) because the original ones are so brittle now, and you might want to replace an early ULA with a later one which formats the video signal properly, or with an FPGA based substitute.

Here we come to the great dilemma we often face - do you want it original, or do you want it working? For me, generally the latter, but If I swap out original parts - for example, the original 1K RAMs in my ZX81s are now 62256s - I do carefully keep the original parts so that any future owner, should there be one, has the option of returning it to original configuration.

Even where original parts are dud and have to be replaced with obviously-not-original parts - such as EPROMs to replace dud mask-programmed PROMs - I keep the original failed parts so the unit can be returned to 'Museum condition' with its original manufacturer fitted parts in place, should that ever be desired.

I also have a ZX81 which came to me already fitted in a Dktronics keyboard - they seem to be more common than I thought. I have one of those Dk keyboard enclosures for my Spectrum as well, bought when they were current, although at the moment the Spectrum is back in its original rubber-keyed enclosure.
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Old 14th Mar 2021, 4:10 pm   #48
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Briefly switching tracks, I thought I had seem Tim mention somewhere that he no longer has an Atari ST mono monitor - for the benefit of those not familiar with the machine the ST has three video modes, two of them are variations on standard-definition 50Hz video and can be displayed on a TV or composite or RGB video monitor, but the third high-resolution monochrome mode required a specific monitor, the SM124 or SM125 which ran at around a 70Hz framerate which most SD monitors can not cope with. (There are a few rareish 'multisync' monitors, much sought after by ST owners, which will cope with all three modes).

It is actually possible to use a common or garden PC VGA CRT or LCD monitor as an Atari ST 'mono' monitor by wiring the mono video output signal (suitably attenuated) to all three R,G,B, inputs of the monitor and by connecting the ST's vertical and horizontal sync outputs to the VGA sync inputs. You also need to strap the 'mono' pin of the 13-way monitor connection to 0V to inform the ST that there is a mono monitor connected.

This works if, and only if, the sync inputs on the VGA monitor are not 75R terminated. If they are, that's too low a resistance for the ST's TTL sync outputs to drive, but if the sync inputs on the monitor have a higher termination resistance - high enough for a TTL output to be able to drive without bursting a blood vessel - then it will work.
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Old 14th Mar 2021, 4:39 pm   #49
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I was surprised about the lack of mainstream coverage as well considering how many could afford the ZX81 assembled - it really was the first machine that anyone could own. Thanks for the extra Views! I do the videos more for my own interest and as a way of keeping a modern blog and diary and to document stuff that might be a bit rarer on the internet for those seeking the information, so gaining subscribers is not a priority but, it is much appreciated that people watch it and especially if they do subscribe for my eclectic mix.

I think I ran the Epson in Epson mode as it spent its life printing out code listings as I too prefer to look through listings on paper so very few codes were ever needed. Posh printing was done on the daisywheel next to it which did need good drivers!

That is really interesting on the Mono monitor for the ST - I will have to try that I have a few VGA 4x9 monitors here hopefully one of them will cope - that will make the ST far more usable again and is definitely the reason for this thread.
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Old 14th Mar 2021, 4:39 pm   #50
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Yes, I remember the corner of a local WH Smiths having these set-up, and later Spectrums. where you could go and type things in and run it.
Although I think one of the first 'Home' computers I saw, was when someone I knew got a UK101.

Whenever I see a used ZX81 for < £20, I'd probably buy it as probably a good investment as it seems all 80's computers are increasing in value.
Although it's been said that eventually the bubble may burst , when all of those of us who were young back in the 70's / 80's are no longer in a position to buy (Although I'd never pay very much just to get a boxed etc. old computer, I'd rather buy a v.cheap faulty one and repair it).

It wasn't that long ago that you could still buy NOS ZX81 ULA's for not too much (I think a new one cost me about £8 from CPC in the late 80's, so that one at least is probably the latest design as they'd stop making them by then). In future it's probably a case of FPGA & EEPROM's (maybe available new for a longer than stopped-production of EPROM's, and no doubt someone could reprint markings, although may need mod for different CS pins) to replace the custom IC's, other than having a large pile of scrap ones, to salvage enough good parts from. I have also since acquired the odd spare ROM / ULA (even a ZX printer one), so wouldn't need to use more modern alternatives yet (although in Commodore computers, these may be much more reliable)

I would now always try and keep old computers in original condition - externally at least. But I'd rather have it working, than not, so I wouldn't have a problem making internal mods, as long as they're easily-reversible and don't involve cutting PCB tracks etc., so adaptor modules are OK.
I think most people buying them, would just want something that looks right externally and functions, rather than opening it up (very risky with fragile membranes!) to carefully check it. Although swapping the internal board for a modern one / RPi etc. is cheating a bit!

For rarer & more-valuable early computers, I would try and use appropriate dated vintage IC's - Luckily I do have quite a lot of old IC's.
I recently managed to almost completely re-assemble some original Acorn System board I found in Rally 50p bags that had been stripped of all (socketed) IC's, from IC's I had + a few old-ones from online. I even managed to have all the RAM IC's with the same date/batch codes.
(As when you spot a whole mixture of IC's on a board, it does give you the impression it's had a bit of a troubled history).

Although, I have been tempted to put a 62256 32K SRAM IC's in place of the 4118 (/ 6116 in USA version?) inside ZX81's, to avoid the wobbly RAM-pack problems, as should be able to do this quite neatly.

With a VIC20 I obtained cheap / free, I found extra RAM on a bit of Veroboard inside, and loads of hard-wiring to the main board. It did actually still work, but I redid them all, as they were close to falling-off.
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Old 14th Mar 2021, 4:44 pm   #51
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Default Re: Enhancing PETs and other Vintage Computers

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Originally Posted by SiriusHardware View Post
Even where original parts are dud and have to be replaced with obviously-not-original parts - such as EPROMs to replace dud mask-programmed PROMs - I keep the original failed parts so the unit can be returned to 'Museum condition' with its original manufacturer fitted parts in place, should that ever be desired.
.
When I repaired my C64 I needed to replace an eprom and a ram chip and I put them in a bag taped inside rhe case for exactly this reason.
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Old 14th Mar 2021, 4:55 pm   #52
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Even where original parts are dud and have to be replaced with obviously-not-original parts - such as EPROMs to replace dud mask-programmed PROMs - I keep the original failed parts so the unit can be returned to 'Museum condition' with its original manufacturer fitted parts in place, should that ever be desired.
.
When I repaired my C64 I needed to replace an eprom and a ram chip and I put them in a bag taped inside rhe case for exactly this reason.
Although some Computer-museums do actually have the less rare models like these running, to play games on etc. Although they tend to have modern design solid-state memory expansion boards plugged-in, and I've not seen any other than Beebs to have magnetic-media / laservision devices attached as would be rather troublesome to keep going.
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Old 14th Mar 2021, 4:57 pm   #53
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I 'celebrated' the ZX81 40th anniversary by loading up 3D Monster Maze and playing that for a while on one of my '16K inside' ZX81s. If you know how frantic that game can be you'll know that the last thing you want is a perilously attached wobblesome RAM pack standing on the boundary between you and early oblivion.

I can now honestly say that the only thing which gets me killed in that game is my own ineptitude, which is nice.

I have considered making a joystick interface using my trademark optocouplers to shadow the five keyboard keys which are almost always used for movement and fire. I might do that on the Dk cased '81, which by its very nature is a modified machine already.
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Old 14th Mar 2021, 5:06 pm   #54
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Quote:
where you could go and type things in and run it
...and then run off.


Quote:
Computer-museums do actually have the less rare models like these running
On the occasion of my visit to The Centre For Computing History (Cambridge) I was really impressed that they had working examples of pretty much every type of 1980s home computer publicly accessable and working. Most had whatever fast-loader solutions were available attached to them, with a selection of software ready to be loaded in a fraction of a second.

At the same time, I felt a little bit nervous for the machines in question, especially the rarer ones. I think TCFCH must have plenty of spare parts available in order for this policy to be feasible.

Some of the machines can obviously take a bit more of a hammering than others, especially the tough old BBC Bs with their excellent keyboards (they had a whole room full of those working).
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Old 14th Mar 2021, 7:13 pm   #55
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For Tim, the wiring for Atari ST mono-out to VGA-monitor-in is in the third post of this thread over on Atari-Forum.com. Note the use of series resistors in the R/G/B inputs.

https://www.atari-forum.com/viewtopic.php?t=31893

Unless your VGA monitor has an integral audio amplifier and speakers (...some do) the mono audio-out from the ST has to go to something like a pair of active PC speakers.

As stated earlier, you need to measure the resistance from each VGA sync input (pins 13, 14 of the 15-way VGA connector) down to 0V, first. If it is anything below about 470Ω, pick another monitor. On real Atari mono monitors the termination resistances of the sync inputs are at least 1KΩ.
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Old 14th Mar 2021, 11:18 pm   #56
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I suppose you could always add a video-amp buffer in-series, if you haven't got a monitor with high-Z, non-terminated inputs.

I do recall that in our Uni uC club, someone had built an ST breakout box, with an audio amp / speaker in it to convert from their rather odd 13pin connector
(trying to compete with Amiga's 23pin D?)
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Old 14th Mar 2021, 11:33 pm   #57
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[QUOTE

At the same time, I felt a little bit nervous for the machines in question, especially the rarer ones. I think TCFCH must have plenty of spare parts available in order for this policy to be feasible.

Some of the machines can obviously take a bit more of a hammering than others, especially the tough old BBC Bs with their excellent keyboards (they had a whole room full of those working).[/QUOTE]


Yes, I've been to the Cambridge CfCH a few times, as well as Bletchley Park's TNMoC that also has a BBC (Class)Room.
And I'd heard they had a good stock of donated Beeb's, to keep them going / had appealed many years ago for people to help fix these.

Whilst at School, I recall the Computer Studies teacher knowing exactly where to hit the lid to fix a problem with the plug-in Solidisk Sideways RAM board, that not only plugged into a ROM socket but also had an edge connector for swapping the RAM daughter board for different sizes.
And also spending some lunchtimes in there helping making these a bit more reliable, by soldering the flying wires onto the jumper pins (rather than the cut-up IC sockets they originally were supplied with to push onto the 0.1" jumper headers)
The machines booted from the Econet, with ability to load ROM images into the SW-RAM from the file server, as well as save to your account's area - so didn't need floppies on them - Although I usually used ones with disk drives and my own disks, once I finally got one at home.
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Old 14th Mar 2021, 11:35 pm   #58
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Being DIN connectors (albeit rather exotic ones), the Atari 13-pin DIN monitor plugs are still widely available for about £3-£4. You do need the hands and the eyesight of a surgeon to wire a cable up to their tiddly, closely spaced pins, and on no account should you forget to slide the plug cover onto the cable first because you only want to have to wire those things up once.

DB19 connectors are/were used on the Atari ST as ACSI (HDD/DMA) connectors and have been hard to find but I have just found this story regarding those:-

https://hackaday.com/2016/06/06/the-...19-connectors/

The Amiga's DB23 video-output connector is very expensive but still available in the usual places.

It makes me wish I had bought 1000 or so of each type when they were a few tens of pence each.
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Old 15th Mar 2021, 11:44 am   #59
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It makes me wish I had bought 1000 or so of each type when they were a few tens of pence each.
I think we all wish we had a handful of cash and a time machine!
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Old 20th May 2021, 7:43 pm   #60
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Maybe julie_m thread hear is not such a bad idea see my proposed plan B to get a working Transam Triton (The Triton-Pi) will need to do some work on interfacing the keyboard.

A level converter board like this 8-channel Bi-directional Logic Level Converter - TXB0108 could work to connect the keyboard to the Raspberry PI GPIO pins.

I used a Triton emulator on a Raspberry PI to check out my eprom's TRAP running on Triton emulator we would need to modify the emulator to talk to the keyboard job done !
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