Voron Klipper Expander and Secondary MCU Guide

Electronics Klipper Guide

Modern Voron builds rarely use a single microcontroller. Between CANBus toolhead boards, chamber controllers, RGB LED drivers, and sensor expansion boards, most Vorons run 2-5 MCUs simultaneously. This guide covers the most popular expander and secondary MCU options for Voron printers: EBB CAN toolhead boards, the Pi's built-in GPIO expander, USB-to-CAN adapters, sensor breakouts, and how to configure them all in Klipper. Last updated: May 2025.

Why Secondary MCUs?

There are several compelling reasons to add secondary MCUs to your Voron:

• CANBus reduces toolhead wiring: Instead of running 10+ wires through the cable chain, run just 4 wires (24V, GND, CAN_H, CAN_L) to a toolhead board that handles all toolhead I/O locally.
• Additional sensors: Add a BME280 for chamber temperature/humidity monitoring, a MAX31865 for PT100 thermocouple reading, or a filament sensor.
• Chamber heater control: A dedicated MCU can run a PID loop for a chamber heater, keeping the enclosure at 50-65C for ABS/PC/Nylon printing.
• Enclosure fan control: Dedicated control for exhaust fans, Nevermore carbon filter fans, and intake fans — all independent of the toolhead.
• Nevermore control: Run a Nevermore activated carbon filter with timed or temperature-triggered cycles.
• RGB lighting: Dedicated MCU for Neopixel or WS2812 LED control without burdening the mainboard.

EBB CAN Toolhead Boards

EBB (EBB = ErCan Bridge Board) toolhead boards are the most popular secondary MCU for Voron printers. They mount directly on the toolhead and handle all local I/O.

EBB36 (CAN v1.1)

• MCU: STM32G0B1 (Cortex-M0+, 64MHz)
• Stepper drivers: Up to 5 (TMC2209 or similar, typically 1 extruder + 4 optional)
• CAN: Integrated CAN transceiver, CAN v1.1 spec
• Inputs: 2 thermistor inputs, 2 fan headers (4-pin), 1 probe input (3-pin), 2 endstop inputs
• Outputs: Neopixel/WS2812 header, servo/6-pin expansion header
• Dimensions: 36x36mm — fits standard Voron toolhead mounting pattern
• Best for: V2.4, Trident, Switchwire with standard SB toolhead

EBB42 (CAN v1.1)

• MCU: STM32G0B1 (same as EBB36)
• Stepper drivers: Up to 5
• CAN: Integrated CAN transceiver
• Inputs: 3 thermistor inputs, 3 fan headers, 2 probe inputs, 3 endstop inputs
• Outputs: Neopixel header, RGB header, 2 expansion ports
• Dimensions: 42x42mm — slightly larger than EBB36
• Best for: V0.2 (more space available on mini Stealthburner), builds needing extra I/O

SB2040 (Stealthburner CAN board)

• MCU: RP2040 (Dual-core Cortex-M0+, 133MHz)
• Stepper drivers: 1 (extruder only, designed for Stealthburner)
• CAN: Integrated CAN transceiver (SN65HVD230)
• Inputs: 1 thermistor, 1 fan header, 1 probe/endstop combo
• Design: Custom PCB that bolts directly onto the Stealthburner carriage
• Best for: Clean Stealthburner builds with minimal wiring

USB-to-CAN Adapters

To connect your CAN toolhead board to the Raspberry Pi (or other SBC), you need a USB-to-CAN adapter. These boards translate USB to CAN bus protocol.

BTT U2C (v1.0 / v2.0)

• The most popular USB-to-CAN adapter for Voron builds
• v2.0 updates: improved power handling, beefier USB-C connector, better termination resistor management
• Integrated 120 ohm termination resistor (selectable via jumper)
• 12-24V input, 5V regulator for CAN transceiver
• Status LEDs for CAN communication and power
• Comes with a case and mounting bracket

Fysetc UCAN

• Alternative to BTT U2C, identical functionality
• STM32-based CAN adapter
• Integrated termination resistor
• Reports as a USB-CAN adapter on the Pi
• Often cheaper than U2C, same performance

CANBus Wiring

Proper CANBus wiring is critical for reliable communication. Here are the essential rules:

Wiring Basics

• CAN_H and CAN_L: These are the two data wires. They must be a twisted pair to reject electromagnetic interference.
• Power: 24V and GND. 24V powers the toolhead board. The CAN transceiver uses 5V, typically regulated on-board.
• Cable: CAT5e or CAT6 Ethernet cable works perfectly. Use one twisted pair for CAN_H/CAN_L, another pair for 24V/GND. The remaining pairs can be spares.

Termination Resistors

CANBus requires a 120 ohm termination resistor at each end of the bus. In a typical Voron setup:

• End 1: U2C adapter has a built-in 120 ohm resistor (enable it via jumper)
• End 2: EBB board has a built-in 120 ohm resistor (enable it via jumper)
• No other resistors should be on the bus

Without proper termination, you'll get intermittent communication errors, retransmissions, and print failures. Check with a multimeter between CAN_H and CAN_L at the bus ends — you should read approximately 60 ohms (two 120 ohm resistors in parallel).

Klipper Config for Multiple MCUs

Klipper natively supports multiple MCUs. Each MCU gets its own section in printer.cfg:

Main MCU (controller board)

[mcu]
serial: /dev/serial/by-id/usb-Klipper_stm32f446xx_12345-if00
restart_method: command

Secondary CAN MCU (toolhead board)

[mcu canbus_uuid]
canbus_uuid: 123abc456def
canbus_interface: can0

To find your toolhead board's UUID, use:

~/klippy-env/bin/python ~/klipper/scripts/canbus_query.py can0

This returns a list of all CAN devices on the bus. The UUID is a hexadecimal string like 123abc456def.

Flashing CANBoot / Katapult on Secondary MCU

Katapult (formerly CANBoot) is a bootloader that enables firmware updates over CANBus — no USB cable needed once installed. Here's how to set it up:

Step 1: Build Katapult

cd ~/Katapult
make menuconfig

• Select your MCU (e.g., STM32G0B1 for EBB36/42, RP2040 for SB2040)
• Set CAN bus interface
• Set clock reference (e.g., 8MHz crystal for STM32G0)

make clean
make

Step 2: Flash Katapult via USB/ST-Link

make flash FLASH_DEVICE=/dev/serial/by-id/usb-Katapult_...

Step 3: Flash Klipper over CAN

python3 ~/klipper/scripts/flash_can.py -i can0 -f ~/klipper/out/klipper.bin -u 123abc456def

Once Katapult is installed, all future firmware updates can be done over CAN without touching the hardware.

Sensor Boards

MAX31865 for PT100

The MAX31865 is a PT100/PT1000 RTD-to-digital converter. It reads a resistance temperature detector (PT100) and communicates over SPI. Use it when your hotend has a PT100 thermocouple that the mainboard can't read directly. Wire it to spare pins on your secondary MCU and add this to Klipper:

[thermistor pt100]
sensor_type: MAX31865
sensor_pin: mcu:spi_cs0
spi_speed: 4000000

BME280 for Chamber Temp/Humidity

The BME280 is a temperature, humidity, and barometric pressure sensor. It connects over I2C. Mount it inside your Voron enclosure to monitor chamber conditions. Klipper config:

[temperature_sensor chamber]
sensor_type: BME280
i2c_address: 118
i2c_mcu: mcu

The BME280 appears in Mainsail/Fluidd as a chamber temperature reading alongside your other temperatures.

Daisy-Chaining EBB Boards

You can connect multiple CAN boards on the same bus. Each board has a unique UUID and Klipper communicates with each independently. A typical chain:

[Pi USB] → [U2C CAN adapter] → [EBB36 toolhead] → [EBB42 chamber controller]

Each board needs its own [mcu canbus_uuid] section in printer.cfg with its unique UUID. The termination resistor should only be enabled on the first and last devices on the bus.

Troubleshooting CAN Communication

CANBus may seem intimidating at first, but once it's working, it's rock-solid. The reduced wiring complexity is transformative for Voron builds — especially on toolheads where every gram of wire drag matters for print quality at high speeds.