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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 4th May 2020, 3:59 pm   #321
julie_m
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Default Re: Zx81

The ZX81 keyboard was never very highly regarded as a keyboard, and one of the most popular upgrades was a "proper" keyboard.

You can easily build something better with tactile switches and copper-strip breadboard.

The ZX cursor keys are 5, 6, 7, 8, 0 (in the same order, left-down-up-right as vi) not 6, 7, 8, 9, 0, and therefore span two half-rows of the matrix. But you should be able to use 4016 / 4066 bilateral switches to simulate keystrokes.
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Old 4th May 2020, 4:12 pm   #322
SiriusHardware
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I stand corrected - I was thinking in any case that by indulging in my usual fetish for optocouplers, the stick could turn on the five opto leds fed from a common supply and through a common return, and the opto outputs could be across any key / row intersection desired, no matter whereabouts in the row / column matrix they might be. Add a bit of switching and you can 'set' the output matrix to match the keys used on a few different games.

I can't remember if the '81 ever came to have a de facto standard joystick, in the way that the 'Kempston' became one of two standards - the other being the Interface 2 standard - on the Spectrum.

My 'Other' ZX81, the one which is suffering from weak UHF output, is in a full sized third party 'Dktronics' enclosure / keyboard - in fact I 'rescued' it from a fellow forum member precisely because it had that rather uncommon form factor. It's in really nice condition as well.

The modern replica replacement keyboard membranes are apparently a lot better than the originals, in so far as any membrane keypad can ever be good, of course.

Last edited by SiriusHardware; 4th May 2020 at 4:20 pm.
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Old 5th May 2020, 8:38 am   #323
John Earland
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Default Re: Zx81

Quote:
Originally Posted by SiriusHardware View Post
I stand corrected - I was thinking in any case that by indulging in my usual fetish for optocouplers, the stick could turn on the five opto leds fed from a common supply and through a common return, and the opto outputs could be across any key / row intersection desired, no matter whereabouts in the row / column matrix they might be. Add a bit of switching and you can 'set' the output matrix to match the keys used on a few different games.

I can't remember if the '81 ever came to have a de facto standard joystick, in the way that the 'Kempston' became one of two standards - the other being the Interface 2 standard - on the Spectrum.

My 'Other' ZX81, the one which is suffering from weak UHF output, is in a full sized third party 'Dktronics' enclosure / keyboard - in fact I 'rescued' it from a fellow forum member precisely because it had that rather uncommon form factor. It's in really nice condition as well.

The modern replica replacement keyboard membranes are apparently a lot better than the originals, in so far as any membrane keypad can ever be good, of course.
I have one of those replica keyboards and they are very responsive.
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Old 5th May 2020, 7:45 pm   #324
SiriusHardware
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Default Re: Zx81

The replacement arrived today, but when I peeled off the original membrane all of the incredibly sticky backing remained on the casing instead of coming off with the old membrane as I rather hoped it would.

I don't want the new membrane to get off to a bumpy start, so I'm going to have to have a think about how to get the old sticky stuff off. IPA barely makes a dent in it. What did you do?
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Old 5th May 2020, 7:59 pm   #325
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The replacement arrived today, but when I peeled off the original membrane all of the incredibly sticky backing remained on the casing instead of coming off with the old membrane as I rather hoped it would.

I don't want the new membrane to get off to a bumpy start, so I'm going to have to have a think about how to get the old sticky stuff off. IPA barely makes a dent in it. What did you do?
I was really lucky-most of the glue came off with with membrane. The bits that did stubbornly remain I rubbed with my fingers, pushing them until they rolled into little balls of glue and then I picked them off. I only used alcohol once everything was clear just to be sure it was absolutely clean.
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Old 5th May 2020, 8:12 pm   #326
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Default Re: Zx81

hair dryer set to high and a used razor blade
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Old 5th May 2020, 8:55 pm   #327
SiriusHardware
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John, yes, that's kind of how I saw it going. Unfortunately it didn't happen that way.

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hair dryer set to high and a used razor blade
Sounds like a plan: I'm a bit worried about the possibility of melting an irreplaceable bit of 40-year old plastic, though.
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Old 6th May 2020, 1:04 am   #328
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Default Re: Zx81

That sounds like roley poly glue. Just roll it up into little balls and pick them off.
A cloth dampened with solvent will get any finger marks off before you apply the new keypad.
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Old 6th May 2020, 11:13 am   #329
SiriusHardware
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I change button membranes all the time at work and I agree that is how it usually goes, but this one was exceptionally resilient. I had to soak it in IPA and use a brass scruffle pad (normally used for cleaning soldering iron tips) before it would really start to break up so I could remove it in the usual fashion.
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