Most USB-to-bus adapters, like CANTact Pro or MeatPi’s Ollie V1 and V2, typically support CAN or RS-485/RS-422 as fixed-function serial devices. The FalCAN Probe by Anders B. Nielsen is a multi-protocol USB adapter based on the STM32F042 microcontroller.
The FalCAN Probe is an open-source USB Type-C board connecting a computer to CAN, RS-485, and full-duplex RS-422 networks. It exposes the MCU’s native USB interface along with SWD and GPIOs, and serves as a small Arm Cortex-M0 development platform.
FalCAN Probe specifications:
– MCU: STMicro STM32F042C6Tx Arm Cortex-M0 microcontroller @ 48 MHz with 32KB flash, 6KB SRAM
– Host Interface: USB 2.0 Full Speed via USB Type-C port
– Interfaces (non-isolated):
– CAN bus via Texas Instruments SN65HVD230 transceiver; enumerates as a GS_USB CAN device when jumper JP4 is open
– RS485 and full-duplex RS422 via dual SP3485EN transceivers
– Expansion:
– 2x 17-pin GPIO expansion headers
– Unpopulated female DE-9 (DSUB-9) footprint for CAN standard pinout
– Exposed USART1 (PB6/PB7) for external USB-to-UART usage
– Header pins for GPIOs, boot configuration, SWD debugging, and bus routing (JP3/JP4)
– Debug: Dedicated header for SWD programming
– Misc: Green and Red status LEDs
– Power: 5V via USB-C, regulated by an on-board MIC5504-3.3 LDO
– Dimensions: TBD (4-layer FR4 PCB ~1.6mm thickness)
What differentiates the FalCAN Probe from similar tools like CANable or Candlelight adapters is its firmware. It uses a fork of the candleLight_fw that supports the mainline Linux gs_usb kernel module, allowing it to be used with standard can-utils without installing custom drivers. The firmware adds support for RS-485 and RS-422 mode switching, and the hardware exposes the STM32 development pins.
Mode switching is handled via jumpers checked at startup. If JP4 is open during reset, the device shows as a CAN interface (gs_usb). If JP4 is closed, it appears as a USB serial port (CDC) connected to USART1 for RS-485/RS-422 communication.
Anders notes that the board is a simple STM32 development board with built-in industrial communication hardware, making it easy to reprogram. It can be used as a bus traffic generator, a CAN analyzer, or turned into an ST-Link–style programmer with custom firmware.
The hardware design files (schematics, PCB layout, Gerbers, and BOM with LCSC part numbers) are available on GitHub under a CC BY-SA 4.0 license. The firmware is available in a separate GitHub repository.
The FalCAN Probe with CAN and RS-485 is available for purchase on iMania.dk for 249.00 DKK (~$36 USD), with prices including 25% VAT for European buyers (VAT removed at checkout for US/International buyers). It ships without pin headers or the DE-9 connector soldered, but an unsoldered male DE-9 is included in the package.
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