ZX81 External Keyboard

Discussions about Sinclair ZX80 and ZX81 Hardware
Becky
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ZX81 External Keyboard

Post by Becky » Fri Sep 07, 2018 1:01 pm

If I wanted to make or repurpose a keyboard to use with a ZX81, is it safe to use the A8..15 Lines and the 5v connections on the edge connector? I know I'd need the pull-up resisters and the diodes, but would it be safe to do so? It would be nice to have an external keyboard which plugs into the back, but I prefer to have a working ZX81!

Cheers.
2x ZX81 / 2xZ88 / Spectrum 48K / Spectrum+ / Spectrum +2 (Grey) / Spectrum +3
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mrtinb
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Re: ZX81 External Keyboard

Post by mrtinb » Fri Sep 07, 2018 1:11 pm

I used Wilf Rigter's schematic to create my own external keyboard controller. I'm sold out of the pcbs I made. It was my first electronics project, so anyone should be able to do it.
Last edited by mrtinb on Sat Sep 08, 2018 6:35 pm, edited 1 time in total.
Martin
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1024MAK
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Re: ZX81 External Keyboard

Post by 1024MAK » Sat Sep 08, 2018 2:55 am

Yes, if using the edge-connector, as a minimum, you need a tri-state buffer (a chip where it's output pins can be switched to be open circuit) and some minimal control and address decoding to control the keyboard data going to the data bus.

Mark

Becky
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Re: ZX81 External Keyboard

Post by Becky » Sat Sep 08, 2018 3:03 pm

Thanks for the replies. Looks like it would be a bit too complex for my abilities. Maybe I should just keep looking out for a Memotech keyboard or something similar on ebay. I imagine they are as rare as hens teeth.

Becky.
2x ZX81 / 2xZ88 / Spectrum 48K / Spectrum+ / Spectrum +2 (Grey) / Spectrum +3
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mrtinb
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Re: ZX81 External Keyboard

Post by mrtinb » Sat Sep 08, 2018 3:22 pm

The German forum has designed a new controller and new keyboard with cherry keys with ZX81 symbols. It might be a product to buy soon.

Edit: Link to keyboard in German forum
Martin
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Re: ZX81 External Keyboard

Post by Lardo Boffin » Sat Sep 08, 2018 5:44 pm

Ooh. That looks nice!
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TMAOne
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Re: ZX81 External Keyboard

Post by TMAOne » Sat Sep 08, 2018 6:28 pm

Lardo Boffin wrote:
Sat Sep 08, 2018 5:44 pm
Ooh. That looks nice!
Indeed!

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1024MAK
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Re: ZX81 External Keyboard

Post by 1024MAK » Sun Sep 09, 2018 12:49 am

Becky wrote:
Sat Sep 08, 2018 3:03 pm
Thanks for the replies. Looks like it would be a bit too complex for my abilities. Maybe I should just keep looking out for a Memotech keyboard or something similar on ebay. I imagine they are as rare as hens teeth.

Becky.
It is possible to solder wires to the existing keyboard connector solder terminals on the underside of the Zeddy board. No need to disturb the existing keyboard or it's membrane.

That way, no electronic components are needed (apart from the switches of course :mrgreen: ).
If you use coloured ribbon cable, you can fit it through the expansion port. Although it may get very tight for space if you have an expansion plugged in.

Mark

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Andy Rea
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Re: ZX81 External Keyboard

Post by Andy Rea » Sun Sep 09, 2018 10:34 am

mrtinb wrote:
Sat Sep 08, 2018 3:22 pm
The German forum has designed a new controller and new keyboard with cherry keys with ZX81 symbols. It might be a product to buy soon.

Edit: Link to keyboard in German forum
are they for sale anywhere ?

regards Andy
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

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Paul
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Re: ZX81 External Keyboard

Post by Paul » Sun Sep 09, 2018 10:53 am

They will be most probably for sale in Mahlerts 2019. Are you and Sirmorris coming?
In theory, there is no difference between theory and practice. But, in practice, there is.

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