The PCB is designed to be inserted into the (micro) SIM card socket of the Sixfab Raspberry Pi LTE Base HAT.
It attaches to the RST and IO pin of the SIM card that are required for APDU tunneling.
To make the IO pin compatible with the Raspberry's UART we add a Schottky diode between RX and TX.
Thanks to Markus Maier for designing the PCB.