Great Prusa i3 MK3/3S replacement board for printer hardware hackers! Ideal for use with Klipper firmware, but Marlin firmware is included. It is essentially a BTT SKR-type board with a 32-bit & 168 MHz ARM Cortex-M4 MCU, but with the Ultimachine Einsy-Rambo (8-bit & 16 MHz ATMega2560 MCU) style connections as used on genuine Prusa printers, so no need to cut and replace connectors! Make sure to install only the driver jumpers for serial UART mode for all the TMC2209! See the BTT TMC2209 v1.2 driver documentation linked below. BigTreeTech doesn't approve of firmware updates over USB, but you can still do that if you replace the stock proprietary BTT bootloader! Because the STM32F407VE processor has pins BOOT0 = pulled-down and BOOT1 = floating / not routed, there are only two ways to update the firmware out-of-the-box: the BTT method of placing a 'firmware.bin' file at the top-level of SD card, or by using the software debugger port ('SWD' socket) with a ST-LINK or similar device. However the bootloader can ONLY be updated via the SWD socket. You can opt to install via ST-LINK an open source USB HID (a no-driver-required serial port) bootloader to allow updating over USB, as is common in the Arduino IDE world. This works by entering firmware update mode for a few seconds after reset, flashing 'LED1' on pin 'PB12', and waiting for a connection, and then starting the normal firmware if the update process timed-out. The routing of two pins on the underside of the drivers are not shown on the board schematic: the 'DIAG' pin on drivers are routed to the axis end-stop pin to utilize stepper stall detection, and the 'VREF' pin on drivers are routed to 3.3 Volts to force a maximum stepper current limit since that is instead programmed via the drivers' serial UART interface. The PINDA probe is also safely connected the same Z-axis endstop pin in wired-OR fashion. 4-star rating because of the BOOT0/1 pins being fixed, and the BTT bootloader being proprietary closed source. https://github.com/bigtreetech/BTT002-V1.0 https://github.com/bigtreetech/BIGTREETECH-TMC2209-V1.2 https://github.com/Serasidis/STM32_HID_Bootloader https://github.com/Arksine/STM32_HID_Bootloader Others: https://github.com/bigtreetech?tab=repositories https://www.st.com/en/microcontrollers-microprocessors/stm32f407vg.html