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.
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
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.
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