• Bugfixes
    • 3.3V regulator added so the SD card isn’t supplied by the reference output of the USB-Serial bridge.
    • Unused inputs on SD card buffer IC are grounded. Stock design leaves them floating.
    • PCB layout fixed to follow standard PCB design guidelines including best practices for Trinamic drivers from the TMC2209 datasheet.
      • Direct ground return path provided for each driver with minimal sharing between channels. Stock config has both channels on 4 drivers share a single circuitous path around the board that introduces current sensing errors.
      • 2x 10uF 1206 ceramic capacitors added as close as possible to each driver chip.
      • Ground planes maximized with via stitching to reduce noise and losses.
  • Improvements
    • Comes with Micro-B USB port standard. Mini-USB ports are not recommended on new designs because the port itself wears down over time and needs to be replaced, which requires soldering. With Micro-USB the cable wears down and can be easily replaced. The PCB layout supports both types.
    • Added second fan control channel with 2 fan connectors for the controller and hotend fans. There is a jumper to select if they are always on or controlled by pin 29/A2 through marlin. They can be setup to turn on/off with either the hotend or stepper motors in marlin.
    • 3-pin probe/bltouch header added with jumper to select beeper/probe for pin 27. Bltouch wire colors labeled on probe and Z stop connectors.
    • 15A ATO fuse added
    • ESD protection diodes added to 24V input, USB 5V+data pins and BLtouch data pin.
    • All other external inputs protected with series resistors and clamp diodes to protect against voltage spikes and accidental shorts during setup.
    • Low RDS(on) MOSFETs for bed and hotend stay cool to the touch with no heatsink necessary.
    • VREF trimmers replaced with high quality sealed units with a non-conductive screwdriver port.
      • .15ohm sense resistors, trimmed to 1.13V (580mA) for X/Y/Z axis and 1.27V (650mA) for E axis.
    • TX and RX pins added to EXT-A2 jumper, to support adding an ESP8266 module for wireless printing
  • Jumpers
    • USB_POWER header allows enabling/disabling 5V input from USB jack.
    • JP2 allows selecting Beeper or Probe on pin 27, external pin 27 board not necessary to add probe.
    • JP_FAN1 controls whether hotend+controller fans connected to FAN1A and FAN1B are always on or controlled by pin 29/A2 through marlin.
  • Status LEDs
    • White LEDs running from 5VOUT on each driver show when they have power.
    • Red LEDs on driver DIAG pins to show when drivers have a fault condition
    • Red LEDs on hotend and heated bed MOSFET gates show when they are heating.
    • Blue LEDs on FAN0 and FAN1 show when part cooling and controller+hotend fan are running
  • Software Configuration
    • Comes with Arduino bootloader installed and latest Marlin 2.0 stable
    • Linear advance enabled with 0.0 k factor by default, which is equivalent to disabling. Can be set with GCODE M900 command, such as with Cura Linear Advance plugin.
    • Babystepping enabled
    • S-curve Acceleration enabled
    • FAN1 setup as hotend cooling fan, so it should run whenever the extruder is over 50 degrees, which should be effective for most use cases.