looking to replace amiga 500 keyboard with custom mechanical board

[Sarreq Teryx]

I just bought (as-is, as a project) an A500, and found out the keyboard membrane was removed by the (or A) previous owner. I have a layout ready, and a PCB in design, but I can't seem to be able to find how the membrane matrix is laid out. if anyone can help me with that, I can trace my PCB accordingly and use the original controller board (or at least components). if not, can anyone help with info to program a µC to interface correctly with the A500?

I have PCBs in design for each of these, I'm leaning toward the ANSI layout though.

ANSI Layout

A500ANSI.png (46.69 KiB) Viewed 6016 times

BigAssEnter Layout

A500BAE.png (46.63 KiB) Viewed 6016 times

ISO Layout

A500ISO.png (46.86 KiB) Viewed 6016 times

[rich1051414]

Is this what you are looking for?

Amiga A500 Membrane2.jpg (109.53 KiB) Viewed 6006 times

This is the big ass enter version.

[Sarreq Teryx]

absolutely! do you have a higher res version?

[rich1051414]

absolutely! do you have a higher res version?

No I do not I googlfu'ed this one. But it seems good enough to make out the traces.

[rich1051414]

Here, I enhanced it to make it a bit easier to make out:

Amiga A500 Membrane Enhanced.png (4.53 MiB) Viewed 5994 times

[Sarreq Teryx]

thanks. not easier enough, though. I'm actually baffled by how hard it is to find more info on this.

edit: I've been trying to run this through my own enhancements, but those tight parallel traces aren't detailed enough to be helpful.

edit: if anyone is willing to pull apart their keyboard, and slap the membrane on a scanner, i'd be super grateful.

[Findecanor]

I am afraid that there could be more than one version of the A500 membrane though.

Here are a couple old pictures I had taken of my membranes: A1200 (top) and late-model A500 (below). Both are ISO (Swedish/Finnish layout). The ISO A500's seems to be very similar to rich1051414's membrane apart from the different keys but the A1200's membrane looks completely different.
You didn't say which layout there was on your Amiga ... Do they use ISO or ANSI on Gallifrey?

[Sarreq Teryx]

I have rev6a motherboard, with a UK BigAssEnter keyboard. I was going to try to make my replacement ANSI.
Most likely, the differences between membrane revisions is only in optimizing traces to reduce copper (ar aluminum?) usage to reduce cost. but the logical key matrix, and likely the connector pinout, should still be the same. at a guess, the A1200 is probably the same as well, despite where the connector is and goes.
any chance of a closer pic of the a500 one?

[czarek]

I think I'll pass. Nothing feels as good as linear space invaders for Amiga games

[Findecanor]

I came across a schema of the Amiga 500 keyboard controller, with matrix and pinout for the membrane connector:
http://eab.abime.net/showthread.php?t=81893

And in KiCad: https://github.com/BleuLlama/AmigaSchematics

I also found a schema for the Amiga 1200's keyboard controller. The membrane connector is different on that one, and it is different also on the Amiga 600's.
The pin/port assignment on the microcontroller is also different.

[Findecanor]

I found that there is a type of Amiga 500 keyboard with membrane/s that has two contacts instead of one. I don't know if it uses something else than Mitsumi KPR Type. I found an image of the contacts but no more details...

According to the Amiga Hardware Reference Manual, all Amiga keyboards are supposed to use (a subset of) the same matrix. The reason for this is stated explicitly that it is so that software developers would be able to avoid blocking key combinations on keyboards that do not have N-key rollover. Very thoughtful of the hardware designers!
Also, the modifiers (Shift, Alt, Amiga, Ctrl) are on its own 1×7 matrix so as to never be part of any blocking key combo.
The HRM also contains a description of the serial protocol.

I found forum posts that said that the Amiga 1200's single 31-pin connector should have the same pinout as the single-connector Amiga 500 membrane.
Edit: I tested my Amiga 1200 keyboard membrane with a multimeter and it checks out!

I traced a picture of a Mitsumi membrane from an Amiga 600 also. The numpad occupies its own row in the matrix — which is simply omitted on the Amiga 600 which does not have one. The membrane connector for the A600 is close to the A500/A1200's: the column pinout is the same but the line for the numpad row is simply missing and the rows, the modifiers' column and the Caps Lock LED have been shuffled around.

[Findecanor]

I see an error in the diagram at the top. The original Space bar is 9 units wide, not 8.5.
I would suggest using a 7 unit space bar and adding a 1×1 key on the left and right sides.
I also suggest making the larger Caps Lock option a 1.75 wide key, which would also be easy to source. That one would leave a 0.5 u wide gap to the 'A' key, but that gap is just as wide as the step on a stepped Cherry-profile Caps Lock key.

As to constructing it, I'm afraid that a complicated metal plate would be required for fitting it inside the computer. The mechanical NMB A500 keyboard is suspended by the plate, resting on the left and right. An extension of the plate is bent twice in the front and slides inside four tabs. The tabs presses against the bent part and prevent the keyboard from sliding forward. Protrusions in the top of the case prevents the keyboard from sliding backwards. In my Amiga 500, a plate 1.5 mm thick fits.

I checked the fit inside the Amiga 1200 also. In that one a 1.5mm thick front plate extension would be a tight fit, however. There can also be additional legs holding up the keyboard inside the case: on the harddrive cage and in some revisions on the floppy drive as well. The floppy leg could be removed and I suppose that most hardcore Amiga 1200 users these days use Compact Flash instead of HDD but I think it would suck to not be compatible with harddrives.

[breech]

You might want to look at the A2000 keyboards, they use a PCB instead of the membrane but are very similar to A500. I would definitely be down for a replacement as the membranes are now suffering from track corrosion.

[Findecanor]

I think I saw replacement A500 membranes out there somewhere if that is the only problem.
But I think a mechanical keyboard would be nicer, giving more options, more possible features ... etc.

BTW. There is also crowdfunding for replacement Amiga 500 cases and keycaps for the Mitsumi keyboards — in multiple colours and in plastics that don't yellow. The cases also have brass inserts for screw threads and mounts for Raspberry Pi and other boards if you want to run an emulator instead of the real thing. (An emulator running on a Raspberry Pi 3 is a few times faster than an Amiga 500s with a 68040 CPU boards and can run AGA etc. etc.)

[Findecanor]

Old thread. Old news. But I heard about it first today. Apparently they have been shipped to customers not long ago:
New Replacement Keyboards from Kipper2k.