Zx81 - Page 17 - UK Vintage Radio Repair and Restoration Discussion Forum

julie_m · 4th May 2020, 3:59 pm

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.

SiriusHardware · 4th May 2020, 4:12 pm

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.

John Earland · 5th May 2020, 8:38 am

Quote:

Originally Posted by SiriusHardware

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.

SiriusHardware · 5th May 2020, 7:45 pm

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?

John Earland · 5th May 2020, 7:59 pm

Quote:

Originally Posted by SiriusHardware

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.

McMurdo · 5th May 2020, 8:12 pm

hair dryer set to high and a used razor blade

SiriusHardware · 5th May 2020, 8:55 pm

John, yes, that's kind of how I saw it going. Unfortunately it didn't happen that way.

Quote:

Originally Posted by McMurdo

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.

Refugee · 6th May 2020, 1:04 am

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.

SiriusHardware · 6th May 2020, 11:13 am

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.

4th May 2020, 3:59 pm	#321
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	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. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

4th May 2020, 4:12 pm	#322
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,091	Re: Zx81 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.

5th May 2020, 7:45 pm	#324
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,091	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?

5th May 2020, 8:12 pm	#326
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,171	Re: Zx81 hair dryer set to high and a used razor blade __________________ Kevin

6th May 2020, 1:04 am	#328
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,536	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.

6th May 2020, 11:13 am	#329
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,091	Re: Zx81 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.