GRBLDuino Mega Shield V1

The GRBLDuino Mega Shield V1 is a 6 axis capable CNC controller shield for Arduino Mega systems running GRBL-Mega. Although the official release doesn’t support more than three axes, there are variants available supporting up to 6.

Shortly after starting the GRBLDuino Uno Shield, I came across some postings about the end of life for GRBL on the Arduino Uno since it is at maximum capacity. The next logical step was to move up to the Arduino Mega version as it had plenty of room for future expansion (and there are a few 6 axis branches out there).


  • Fits on Arduino Mega (4.79″ x 2.90″).
  • On board reset button.
  • All GRBLDuino are based on the Pololu DRV8825 stepper motor drivers and are compatible with all pin-compatible equivalents.
  • Maximum input voltage of 45 volts DC (genuine Pololu DRV8825 max voltage)
  • Jumper selectable high/low limit switch activation.
  • RC filters on limit switch and probe inputs.
  • All machine connections are broken out to screw terminals.
    • + and – Limit switches for each X, Y, and Z axis (only one per A, B, and C).
    • Resume, Hold, Abort, Emergency Stop, Door Safety support.
    • Flood and Mist coolant connections.
    • Spindle Enabled, Direction, and Speed (PWM) connections.
    • Probe connection.
  • 6 independent (X, Y, Z, A, B, C) axes or 3 independent (X, Y, Z) and 3 clone (A, B, C) axes.


The schematic is pretty straightforward – it shows all of the internal connections on the board and external connectors.

GRBLDuino Mega Shield V1 Schematic

GRBLDuino Mega Shield V1 Schematic

Bill of Materials

  • 1x GRBLDuino Mega Shield PCB
  • 21x Two position screw terminal blocks
  • 12x 1×8 female pin headers
  • 1x 1×3 male pin headers
  • 6x 1×4 male pin headers
  • 1x 1×6 male pin headers
  • 5x 1×8 male pin headers
  • 6x 2×3 male pin headers
  • 6x 2×6 male pin headers
  • 1x 2×18 male pin headers
  • 1x tactile switch
  • 1x 10k ohm resistor
  • 2x 680 ohm resistor network
  • 7x 150nF ceramic capacitors
  • 6x 100uF 50v electrolytic capacitors (genuine Nichicon)
  • 18x short 2 pin jumper shunts
  • 7x long 2 pin jumper shunts


The machine connections are listed in the image below.

Gerber Files

For those wishing to make their own board, the Gerber files are provided. There are no guarantees made to accuracy or completeness of these files.


I anticipate these being available for sale through a few outlets beginning in early April. Kits will sell for around $25 shipped in the US and assembled boards will sell for around $45 shipped in the US. Once available, the best price will be at the Eccentric Workshop store, but they will also be on Tindie and eBay.

Future Versions

Version 2 will likely drop full 6 axis support (back to 4 for reduced BOM costs) and introduce relay drivers on the coolant and spindle enable lines to control external devices. A version with the Arduino Mega integrated with the shield is also in the works.



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