TI99/4A KEYBOARD ADAPTATION

Discussions about Sinclair ZX80 and ZX81 Hardware
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gammaray
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TI99/4A KEYBOARD ADAPTATION

Post by gammaray » Sun Dec 17, 2017 2:05 am

I had been interested in using an Apple Keyboard for replacement and case for mounting (too short for some of my schemes)

but danmoore used the TI99..
IMG_1380-tny.jpg
IMG_1380-tny.jpg (276.01 KiB) Viewed 1124 times
Looking at it's matrix, it seems much simpler to implement! It already has the 8x5 matrix!
keyboard_schematic.jpg
keyboard_schematic.jpg (70.53 KiB) Viewed 1124 times
Except for the Z X C V B keys shifting as well as N M and the various control keys, the rest of the keys fall in line with the TZX81000 matrix.

A little rewiring and special circuitry could result in almost perfect replacement.

Maybe Dan would like to show us what he did do?
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

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mooredan
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Re: TI99/4A KEYBOARD ADAPTATION

Post by mooredan » Sun Dec 17, 2017 10:35 pm

I did same mod some thirty-odd years ago too. I think that I was able to get a new TI-99/4A keyboard back then, but now I couldn't find a new one. So I camped out on ebay waiting for a junk TI to come along - got one for $12 + shipping. Get the one with the black keys, then you're assured that you'll get the switch type versus membrane type that is reported to be in other models.

After looking at the photos, it looks like I was a bit sloppy in the trace cuts and soldering. My wife has commandeered my magnifying lamp for her artwork hobby. ...excuses, excuses, ....

(click on the following photos for a full sized photo)

Image

The red circles are where I cut the traces, and the blue boxes are the keys I removed to match it up with the original keyboard. With the exception of the additional space/pound key to the right of the M key -- that one isn't wired correctly yet anyway (I'll fix it shortly). Others with this keyboard have kept the additional keys and duplicated certain ones.

Image

Still needs to be cleaned up a bit and I plan to cut up a junk ZX81 keyboard and glued the them onto the key caps -- but it doesn't look like the functions will fit -- may have to either exclude them or shrink them.

I have a small metal cabinet coming for mounting this.
Dan Moore
Portland, Oregon, USA

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gammaray
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Re: TI99/4A KEYBOARD ADAPTATION

Post by gammaray » Mon Dec 18, 2017 12:56 am

Can the TI99/4A cabinet be adapted?
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

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mooredan
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Re: TI99/4A KEYBOARD ADAPTATION

Post by mooredan » Mon Dec 18, 2017 4:12 am

I don't see why it wouldn't fit. Back in the early '80's I had put it in a nice sloped console/cabinet that I got from Radio Shack. Heavy duty metal, broke one set of nibblers cutting it.

Image

Here's the box that's on its way:

Image

The width is just right for the keyboard.
Dan Moore
Portland, Oregon, USA

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gammaray
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Re: TI99/4A KEYBOARD ADAPTATION

Post by gammaray » Mon Dec 18, 2017 5:51 pm

Nice now don't forget decals for logo!

Mooredan>>
Still needs to be cleaned up a bit and I plan to cut up a junk ZX81 keyboard and glued the them onto the key caps -- but it doesn't look like the functions will fit -- may have to either exclude them or shrink them.
I cut up a laser print of keyboard with clear nail polish as adhesive and finish coat. Try on old PC key first to get the hang of it.
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

vwbz80a
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Re: TI99/4A KEYBOARD ADAPTATION

Post by vwbz80a » Tue Dec 19, 2017 1:46 am

Excellent.

Becky
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Re: TI99/4A KEYBOARD ADAPTATION

Post by Becky » Tue Dec 19, 2017 10:34 am

That is a lovely tidy job. I rewired an Electron keyboard to use with my speccy clone, but it was like sphagetti. You said that you had removed some extra keys. Did you not consider keeping one as a reset key? I did that with my Harlequin (Used the ESC key), but it was easy because there was a reset header on the board. Maybe with a zeddy it might be more complex to reset the cpu.

Again, brilliant job.

Becky.
2x ZX81/ 2xZ88 / Spectrum+ / Spectrum +2 (Grey) / Spectrum +3

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1024MAK
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Adding a ZX81 reset button

Post by 1024MAK » Tue Dec 19, 2017 11:48 am

Adding a ZX81 reset button

Connect a push to make switch across the connections for C5 (1uF) or between "pins" 21A (component side) and 4B (underside) on the edge-connector.

If you intend using "normal" keys on a replacement keyboard, pick a key in the corner, so it is less likely to be accidentally pressed. Or better, wire two different keys in series, so that both have to be pressed to reset the computer ;)

Mark

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Paul
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Re: TI99/4A KEYBOARD ADAPTATION

Post by Paul » Tue Dec 19, 2017 1:06 pm

If you add a small resistor of about 100 ohm this will be better for the capacitor and the switch.
In theory, there is no difference between theory and practice. But, in practice, there is.

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mooredan
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Re: TI99/4A KEYBOARD ADAPTATION

Post by mooredan » Thu Dec 21, 2017 8:47 am

That reminds me, I do plan on doing some debouncing mitigation on the keyboard. I seem to recall this sometimes showing its face. Here's a good reference: http://www.labbookpages.co.uk/electronics/debounce.html
Dan Moore
Portland, Oregon, USA

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