A500 Mini Keyboardification Chapter two, part 3 – PCB’s

I’ve spent a couple of days designing, and and a today, spent nearly a hundred quid at JLCPCB ordering a bunch of prototypes

The first revision of the Keyboard PCB
First ‘space sample’ of the top mounting board.
Floppy Disc Micro SD card holder!
Rear of the floppy discc.

I had to bite the bullet and spend some money as I now need to move on with the Keycap CAD. I have a big concern about the fitting of the printed keycaps onto the smaller switches. I’ve gone with ALPS switches as they used to be a huge brand name back in the day and i’m hoping should provide some consitency.

The prototypes will help also to test and develop the PRK Firmware i’m planning to use.

The ‘Clamp’ adaptor is fairly non-functional. It has a Rasperry Pi Pico footprint onboard and a 40 pin FPC style connector to act as a ‘stand-in’ for the Raspberry pi Pico which is currently on the back of the main PCB.

The whole idea of the ‘clamp board’ is to allow an ‘ease’ of installation – I’ll use some Pogo Pins to sit on the test pads by the 3 USB sockets on the back of the A500 Main board.

The plan is to have a basic matrix keyboard PCB, which connects to the clamp board via the 40 pin FPC.

The clamp then accesses the USB and hopefully it can all be fairly easy to assemble.

I’m also testing the Fake floppy connection with the clamp board – no idea if that’ll work or not, we’ll see.

Now the long-ish wait for Aliexpress to deliver my connectors, pogo pins, and a couple of weeks for the Cheapest post option of JLCPCB to ship the assembled keyboard! – nearly 100 switches and diodes on this one, those can be automated in assembly. I’ll need to hand solder on the rear the FPC connector but those are easy enough!

A500 Mini Keyboardification Chapter two, part 2 – Progress

This one’s a good ‘un

Progress to date has been surprisingly quick – most of the ‘easy’ stuff is now done and I’ve added some extra functionality. Most of the research is now done – have spent waaaaay too long googling connectors, Pogo pins and component types / dimensions.

First print of the keyboard PCB and CAD fitout – pretty close

My workflow generally is to eyeball, sketch, measure, adjust….Then when it’s close enough, i’ll print on paper, adjust in CAD, print again then………3D print

a 3D printed space sample

I’m quite chuffed – the first 3D print seems to fit reasonably well! – there’s some adjustments needed, mainly the top of the keycaps are a little too wide, but overall for a first run, not bad.

The PCB outline

To work out a PCB outline, I’ve scanned the A500 Mini on a flatbed scanner and trace around the important parts, measuring many with calipers

the Keycap CAD
Another view – the big circles are the curves / slight indents in the top of the kecays
The CAD compared to a scan of the actual A500 Mini

Before I 3D printed the sample, I put the A500Mini on a flatbed scanner to match up the holes – as you can see, it’s pretty darn close! – you’re seeing a canvas underneath the actual CAD model of the keycaps in Fusion. The Enter key is black as i’d discovered a slight profile error, so spent half hour correcting a 0.2mm height error πŸ˜›

But, wait, there’s TWO

During the design phase, there’s a process of discovery. My main discovery for the A500Mini keyboard was that….I’d possibly need TWO PCB’s!!

If you look above at the underside of the keyboard you’ll see that there’s no space on the top for electronic components! The PCB needs to mount entirely flush to the case of the Mini. This means I’d need a PCB assembly service that can handle double sided boards (a possibility) – And to also consider a two PCB solution. There’s cost and ease of install considerations for both ways.

The A500Mini has a number of test points on the back, I think using Pogo Pins I can maybe make a clip-on PCB that can securely tap off the USB test points, meaning, a solderless install! – hence the upper white PCB that sits in place of the A500 PCB above

And, now I believe I’m going to go with a THREE PCB solution…….because…

the one with the holes in sits above the stock PCB

That’s a scale floppy disc! with a Micro SD card in
quick render of the floppy slot in the case

I saw a few posts on facebook linking to a guy that’s made a ‘fake’ floppy insert for the A500Mini – https://www.printables.com/model/170947-amiga-500-mini-a500-mini-mini-floppy-disk?fbclid=IwAR3if5FRp3opclhKoTyrkUe63XQtRW-mckg2ymWSKKi1cZvSk1KuRRkzmR4

I figured I’d go one better and make a REAL fake floppy disc. and, the best thing, after several solid days of research and CAD testing, I believe it can work πŸ™‚ – it’ll only need two small cuts inside the A500 case and be totally stock outside. there’s a little more tweaking needed for the floppy disc design to make the MicroSD slot more elegant . I’ve ordered a whole bunch of parts to physically trial this and see if it’s viable.

So, Summary. Still a long way to go, the Keyboard itself is the priority here, the ‘floppy disc’ is just a whimsy on my part for the time being, its development is secondary and may not even make it to a real release if it’s not robust enough.

Keycap CAD – Cosmetics finished, Just needs the ‘switch’ solution figured out

Main PCB – Outline finished, needs routing, quick job to finish

Secondary PCB – Outline finished, needs routing and Pogo Pin solution testing

Tertiary PCB for the floppy disc connector – Concept – parts ordered

Fourth + Fifth PCB’s – the floppy disc itself – parts ordered.

Firmware – Standard keyboard layout is done! – Just needs tweaking and testing on a real A500 Mini

A500 Mini Keyboardification Chapter two, part 1…The Evisceration and Dimensionality

I received yesterday my A500 Mini! – Haven’t even powered it up yet πŸ˜›

My assumption about the 43ish percent scale was about right – and the work i’ve done so far on the PCB pretty much stays the same – which is a relief.

However, till now i’ve been using a full sized Amiga 500 to infer dimensions. I can’t easily do that going forward as the scaling factor for the Amiga is ‘a bit weird’ – I think I can see why it’s been done, but, it’s far far easier to re-start the CAD from new…or at least shift the fusion timeline back to the beginning and see what i can recover πŸ™‚

Much more to do, will update later as there’s also a few ‘gotcha’s i’ve found, and a few ‘woo’ moments also!

Dimensioned to within about 0.3mm

Spmeone should hide my screwdrivers