This hat gives you a CCID/PCSC Compatible Smart Card interface that can connect over UART through a standard Raspberry Pi GPIO header. (Uses the SEC1210UR2 or SEC1210 URT serial interface) and also gives you a USB-C socket that you can use to power your device.

Available in three variants, one for full sized cards and one for sim sized cards and one that has slots for both. (Though you can only use one slot at a time)

Can be used for SeedSigner + Satochip functionality with this fork of SeedSigner here: https://github.com/3rdIteration/seedsigner

Will also work with all normal smartcard functions via the standard Linux CCID driver (https://github.com/LudovicRousseau/CCID) for versions above 1.6.2. (See my GitHub repo for seedsigner-os for an example configuration file)

PCB Fabrication Notes

PCB Thickness: 1mm is best in terms of cases and giving you flexibility in terms of how you connect it. (Directly, with stacking header, etc)

Sim Size, Full Size or Dual Slot

This project is for the dual slot configuration, with a soldered stacking header.

If you want to remove any functionality, you can edit the BOM list to reflect the desired reader slots. (The top side can accommodate either a SIM or Full Size slot socket, the bottom side can accommodate a SIM socket) The PCB can then be trimmed with something like Tin-Snips (Easy on a 1mm board)

eFuse

The current part list will have the eFuse cut off the input voltage around 5.3v which is quite conservative, but should work with the vast majority of USB power supplies. You could also swap out R34 with a 27k resistor for a bit more headroom.