Nobody is perfect...

My first take on a full size keyboard PCB failed after I realized some major design flaws (just after finishing).

So I decided doing it more step-by-step and came up with the  `Poly Keyboard Atom`. One PCB per key. The `Atoms` are compatible with Cherry MX key switches (3 or 5 pins).

Yes, we are at version 2.1, I already tinkered around quite a bit and as you could see from the first picture I missed some pull-up resistors, so it took some time to get this little PCB design right.

The rendering is missing the tiny OLED display with the name `P34107` which has 72x40 pixels. It is connected to the `Atom` via a flexible cable that first goes through the RGB slit (turned out that just some key switches have a wide-enough LED slit) of the key switch and then through the PCB via the cutout.

Unfortunately, the flex cable is not long enough, so it has to be extended. To do that you need some low temperature solder paste (eg. something that melts around 138 centigrade) and a hot air rework station to solder the two flex cables together.

Some more pictures for a clearer view (here 4 Atoms in a row):

On the first photo the flexible cable was still a bit too long, I'm still experimenting here a bit, but it looks like an extra of 30mm is close to ideal.

By looking at the PCB design, you will recognize that the key switch is mounted south-facing so that we can abuse the LED slit of the key switch and get the flexible cable from the OLED display through that slit (and the PCB, since the connector for the FPC is on the backside - on purpose, the flexible cable needs some space to move).

Still, I wanted to have individual LEDs so I added a "north-facing" `WS2812B-Mini` which might need a little opening in the keyboard plate if you don't have transparent key-switch housings. Of course the LED is entirely optional, everything will work without the LED, or I could just add them for the "outer-edge" keys and use them for background lightning when covered by the plate.

Here is a brief pin-out of the Poly Keyboard Atom PCB: