CNC Shield V3 for Arduino UNO R3 and A4988 or DRV8825 Drivers

CNC Shield V3 expansion board for the Arduino UNO R3 and compatible ATmega328P-based boards. It can be used to build controllers for small CNC machines, laser engravers, plotters, positioning systems and other stepper-motor projects.

The board distributes Arduino control signals to Pololu-format motor drivers and provides the usual connections for motors, limit switches and auxiliary functions. It cannot drive motors by itself: a suitable Arduino, drivers, power supply, motors and firmware are also required.

Main features

• Shield format for the Arduino UNO R3.
• Four stepper-driver sockets: X, Y, Z and A.
• Dimensionally compatible with Pololu-format drivers such as the A4988 and DRV8825.
• Jumpers for configuring each driver's microstepping mode.
• The A channel can be configured with jumpers to clone the X, Y or Z movement.
• Connections for four-wire bipolar stepper motors.
• Inputs for limit switches and auxiliary control connections.
• Separate terminal for the motor power supply.
• Compatible with GRBL-based projects, subject to the board revision and firmware configuration.

Arduino compatibility

It is primarily designed for the Arduino UNO R3 and compatible boards using the same physical format, pin arrangement, 5 V logic and ATmega328P microcontroller.

A physically matching connector does not guarantee full compatibility with the Arduino UNO R4, Mega, Nano, ESP32 or other boards. These models may use a different microcontroller, logic voltage or pin mapping and may require different firmware or an adapter.

For Arduino Nano-based projects, the CNC Shield V4 for Arduino Nano is a possible alternative, but it is a different board rather than a direct replacement.

Compatible drivers

The sockets are intended for stepper-motor drivers with a compatible Pololu-format pin arrangement, including:

• A4988 stepper-motor driver.
• DRV8825 stepper-motor driver.

Before inserting a driver, carefully check the position of VMOT, GND, ENABLE and the other pins. The adjustment potentiometers on A4988 and DRV8825 modules may be located on opposite sides, so the potentiometer position must not be used as the only orientation reference.

Maximum current, permitted voltage and microstepping resolution depend on the installed driver, its cooling and the motor. The CNC Shield does not increase the electrical limits of the driver.

Axes and motors

Standard GRBL firmware for the Arduino UNO normally controls three independent axes: X, Y and Z. The fourth socket, marked A, can clone one of these axes through the configuration jumpers, which is useful for machines using two motors on the same gantry.

The A socket should not be presented as an independent fourth axis when using standard GRBL. Using it in this way may require custom-compiled firmware and a review of the D12 and D13 pin assignments.

Machine compatibility

This board can be used in custom projects such as:

• Light-duty three-axis CNC milling machines.
• DIY laser engraving and cutting machines.
• Drawing and writing plotters.
• Positioning machines and small Cartesian robots.
• Educational stepper-motor control projects.

It is not automatically a direct replacement for a commercial machine merely because that machine uses NEMA 17 motors. The electronics, drivers, motor voltage, limit switches, spindle or laser control and firmware configuration must also match.

GRBL and pin mapping

The shield can be used with GRBL firmware for the Arduino UNO, but some connections change function depending on the firmware version and compiled configuration. In particular, variable-speed or PWM spindle and laser control may swap the functions associated with pins D11 and D12, also affecting the Z-limit input.

Before connecting a spindle, laser module or limit switches, check the schematic for the specific board revision and the pin map used by the installed GRBL version.

Power and safety

Motor power is connected to the CNC Shield screw terminal and must not be drawn from the Arduino USB port. Use a power supply with voltage and current ratings suitable for the installed drivers and motors.

Do not connect or disconnect motors or drivers while the system is powered. Before the first power-up, check the terminal polarity, the orientation of every driver and its current-limit adjustment. Reverse connection may damage the driver, CNC Shield or Arduino.

Package contents

• 1 CNC Shield V3 for Arduino UNO.
• Configuration jumpers.

Arduino UNO, A4988 or DRV8825 drivers, heatsinks, motors, power supply, limit switches and wiring are not included unless expressly stated.