Sinclair ZX80 / ZX81 / Z88 Forums

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.. Looking at it's matrix, it seems much simpler to implement! It already has the 8x5 matrix!
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?

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)



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.



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.

Can the TI99/4A cabinet be adapted?

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.



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



The width is just right for the keyboard.

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.

Excellent.

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.

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

If you add a small resistor of about 100 ohm this will be better for the capacitor and the switch.

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