A500 Mini – Quatre

First ‘proper’ spacing test for the SMT switches

First Proper scale PCB layout for the A500 Mini. it mostly looks like it’ll work – BUT, there’s some problems.

I’ve highlighted the problematic switches with white blocks

The Problem – Having switches at 0 degrees or 90 degrees means at some point, due to the staggered keyboard, some will overlap. I’ve spent a few hours optimising the rotation of the switches to reduce the number of overlaps to a minimum, AND, to give all those overlaps a common ‘thing’ that possibly provides one way of easily fixing this.

Zoomed in view

I’ve made it so that Every ‘overlapping’ switch has the bottom left pad causing the overlap. This means, with the right switch type, I can simply cut off this leg for each of the 8 problematic switches and have the keyboard work just fine!

In Most SMT switches this size, there’s 4 legs, but often only 2 are used, (single pole) or sometimes there’s 2 separate switches inside (double pole). provided I use the correct two pins, they should just work fine with 3 legs soldered in. This isn’t exactly an industrially abused keyboard, so 3 legs is plenty of mechanical support.

BUT – I’m unsure if I could ever convince a PCB assembly house to cut a leg off the switches and solder them at a reasonable price, meaning that I may need to solder these 8 manually myself.

There’s a potential other fix also – Rotating the switches at ‘odd’ angles!

If you squint closely, there’s now no overlapping pads on the switches, However, this comes with potential issues

1 – Manufacturing, companies may not want, or be able to put switches on the PCB at arbitary angles like this

2 -Available space within the A500 Mini is currently unknown, which may not give me enough height to be able to do this.

Physically, a 6mm switch, placed at 45 degrees ‘just’ fits within the available 9mm envelope for each 50% scale switch

Rotate that square and you get a circle – which is less than 9mm, which is less than the keycap size!

What this means –

If I rotate the switch, I will not be able to have a recess on the keycaps. On the C64Mini, to keep the keyboard profile height correct, the switches sit about 1.5mm into the keycaps when pressed down. Without this recess, the new keys may need to sit higher than they should. But, this depends on how much space is available underneath the fake keyboard in the mini – it should be possible to add some spacers in to bring the height back down.

The switches sit inside the keycap on the C64Mini keyboard kit

So, The big summary is, Right now, there’s no roadblocks to making this work. a Fully automated production is preferable to bring costs down, so i’ll keep working down that route.

Things to do –

Contact PCB manufacturers to figure out manufacturability

Everything else!


Author: Bleugh

Early Fourties, Wife, two kids in primary school. Both of us work full time...5 years now we’ve been Back in Blighty after a decade away...It's a new country for everyone! Still finding time to tinker!

3 thoughts on “A500 Mini – Quatre”

  1. While I love the c64 mini and the mechanical keyboard you made, and like your enthusiasm to do the same for the A500Mini, I am not sure if it as successful. For once price and delivery times exploded after brexit. I still wait for an order of a britsh shop I made Xmas (and postage was high…). Also an Amiga Emulator needs a CD-drive, as there is still an Amiga magazine with cover CD (Amiga Future). Not meant as critique on you keyboard but on the hole concept of marketing the Amiga as a console in mini size by retro computers. Of course I am a bit influenced by personal history, as unlike with the C64 I used my Amiga as a real computer and less than 50% for games. But I like the mouse and gamepad and preordered them.
    For myself I decided to do an A600 emulator instead. A size between the A500mini and a real Amiga 500. Big enough for a Pi, CD-drive and even floppydrive – and also a mechanical keyboard (aeberbach on github, an usb-controller from thinghacker also on github) with Cherry or compatible switches (TKL). An A600 case is still printable on an Anycubic Chiron… With a Pi 4 (or if I set my timetable more realistic: Pi 5 or Pi 6?) even good for productive use with Raspbian. Anyway, as I had (and still have) an A2000 (A) Rev. 4.x Braunschweig edition with the one and only Amiga Cherry keyboard, of course real Retro feeling can only archived with Cherry black switches anyway 😉

    Liked by 1 person

    1. Thanks for the post 🙂 Love your enthusiasm. I’m doing these projects, mainly for ‘me’ – it’s a great distraction from real life sometimes!. The A500 mini keyboard thing is my first real attempt at trying to sell a complete ‘plug and play’ product!. Yes, i’m really hoping that this will be a “no assembly required” or extremely little asssembly product that requires very little technical ability from the end users. Already, the financials are looking good to have something available, assembled, for a similar cost to the kit.

      a double benefit of developing this product, the underlying code, and the production process can be largely re-used for another project i’ve been working on this past 12 months, it all links together 🙂

      and, who knows, with my new larger 3D printer, and a working Amiga keyboard, it’s not unfeasible that other case styles could follow. couuld you imagine, a raspberry Pi CM4 based amiga style thing!, maybe in a few years at my rate of development 😛

      Liked by 1 person

      1. Yes, thats definitly a great project.
        One hint for the keycaps: I sucsessfully used DyeSub on resin keycaps. As resin is a duroplast, not a thermoplast, it does not deform. While it can degrade under high temperature, the 75 sec. you need for dyesubbing are easaly withstand (unless you apply to much preasure, I broke one key). So dysub is a great method to label keycaps also for self printed keycaps, as long as the labels are darker than the keycap (so no CDTV and CD32 Amiga keyboards this way).
        While on the C64 embossing the labels into the cap and manually colouring them is the best way, there is one big difference: The C64 has the same labels all over the world, while the Amiga has a language dependend keyboard. So embossing letters would have to be done different for every language. Using DyeSub is much more flexible there.
        Thinghacker and I have a nice public discussion about making a mechanical A600 keyboard with controller and self printed keycaps. Thinghacker had the great idea of using the two unused keys in US-layout for function layers (so the blank key right from the left shift would be function key; combined with F2 F12 is been send – quite usefull to get into settings on the emulator. The blank key near ISO-Enter he uses for a media-key layer (nothing I use normaly). Sadly international layouts use this keys already, so I decided to reuse the Caps lock for function key (as Caps lock is a mostly useless function anyway) and map the Caps Lock function to CapsLock+Ctrl. These are some considerations maybe usefull on your project also.
        Today I start printing an A600 keycap set in while and gray. My tests so far were with green resin (as I got two bottles with my printer), but as now all keycaps have the final design (OEM profile) exept missing LED window on CapsLock, I now making the keycaps to be printed in (mostly) original colours, as dyesub on translucent green do not look best due to a lack of contrast.
        You can find the discussion/blog about the A600 mecanical USB keyboard here https://github.com/thinghacker/Amiga600KeyboardUSBAdapter/issues/1

        Liked by 1 person

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