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Abrar , 09-30-2025, 11:42 AM

Hi @Robert Feranec ,
It's been a great pleasure watching your keyboard development series. And I started my own keyboard development project using **RP2040**. but I want to create a **75% **layout **modular** keyboard that has some unique features:

1. 82 switches and 4 rotary encoders on the main board,
2. hot-swappable num-pad module with side-mounted
magnetic pogo pin connector.
3. a castellated mounted RP2040 4-layer SOM module(to keep key-switch pcb board at 2-layer)

But I am facing some problems:

1. RP2040 GPIO pins are limited
2. Not enough space available to mount the SOM module on the switch board
3. Uncertainty about whether using the RP2040’s ADC channels in the key matrix could cause issues

I would really appreciate any suggestions.

Robert Feranec , 09-30-2025, 01:28 PM

this is working ok

Robert Feranec , 09-30-2025, 01:28 PM

Abrar , 10-03-2025, 10:17 AM

Thanks @Robert Feranec for your suggestion on the ADC channel.
I have an issue with space management with placing the RP2040 SOM module in the keyboard pcb. there are barely any space left on the keyboard pcb. now I can think of some ways.
* make the **RP2040 SOM** module **10.5mm*40mm** with and fit it under the **first row**(marked in the pcb)
* make the RP2040 SOM module bigger and fit it beside the **space-key bar**
* if I fit the SOM module beside the space-key bar, the usb differential traces will be longer. not sure if it will cause any data interruption
* should I make the SOM module with **castellated pins** or **normal pad under the back layer**

Robert Feranec , 10-03-2025, 10:42 AM

maybe where the right shift and enter are you may have more space? also, maybe the module doesn't have to be rectangular if you need to fit it there? castellated holes may be useful if you will have to solder it by hand.