Amazon.com: DEVMO Mach3 USB Interface Board USB CNC Controller 4 Axis Motion Control Card Interface Breakout Board for Stepper Motor Driver : Electronics
DIY CNC Controller: How to Setup Your Arduino & gShield
USB Pendant | OpenBuilds
CKD test - Mach3 & Arduino UNO - external DRO & Hotkey via MODBUS - YouTube
My experiments with Mach3 ModBus and Arduino, Part I