J2 connector ( towards camera side) : pin 1 (lens_gnd) and 3 (logic_gnd) are connected Under Linux, it is recognised as USB mass storage PCB version: EF-NEXIV_V2.3 date code: 20201223 U3: The MCU is a STM32F103T8U6 , cost ~USD 2 U1: W25Q?? serial flash ? There are 4 through holes labelled as G D C V, which is deduced to be ST-Link port G: gnd. connect to pin 1 of J2 V: Vcc. connect to pin 5 of J2 D: SIO, serial data. TBD C: CLK, serial clock. TBD Estimate BOM cost is USD 10 or less Viltrox EF-NEX II