And yesterday is… today 
It’s really that good.
The picture shows a 4+4 key and the driver I was working on at the time I ordered the key. The DD+1 driver is 17mm and just there for size comparison.
The key-pcb is 10mm x 27mm, at the pogo-pins the pcb is only 5.6mm, that will fit about anywhere. When you only use 3x3, you can file the key even narrower.
Pcb width is 0.8mm. Pogo-pins are 0.68mm diameter, 16mm long. Via drills on the driver are 16mil (0.4064mm). Distances are 1.3mm between left and right vias and 1.5mm between up and down vias.
Just programmed a driver and it’s a hoot.
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The size of the key is perfectly fine, can be put between thumb and middle finger with the index finger on top, gently pushing the springs of the pogo pins down. With 6 vias, aligning is of course a breeze.
Refined the key a bit, not much really. I’ll make at least two versions:
- A neutral one marked from A to H, where up to 4+4 can be used. With connectors any combination can be plugged on the fly
- A key marked with the pin numbers of the Attinys in my preferred layout
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EDIT: I shared them here