Turning a Raspberry Pi Into a CNC Controller with Linux CNC — and a GPIO-Connected Parallel HAT

Pseudonymous maker "audioartillery" has penned a guide to running a computer numeric control (CNC) mill or other device from a Raspberry Pi single-board computer — directly, using its general-purpose input/output (GPIO) pins rather than an external controller board.

"This article is about using LinuxCNC on Raspberry Pi microcomputers for control of a CNC machine," audioartillery writes by way of introduction. "It will specifically focus on direct control of CNC machine stepper motors with the Raspberry Pi I/O [Input/Output] pins (as opposed to with an Ethernet based control board such as Mesa)."

Raspberry Pi single-board computers are no uncommon sight in CNC, robotics, and 3D printing projects, thanks to their relatively high performance for their size and cost. What is less common, though, is to see the GPIO header being used to directly control said devices — with the Raspberry Pi usually given more of an orchestrating role and the hardware interfacing being left up to dedicated controller boards, typically connected over USB or Ethernet.

"You may have heard that a Raspberry Pi can't directly control stepper motors and you need an Ethernet based controller (Mesa etc) or an MCU [Microcontroller] based controller (Arduino, etc)," audioartillery explains. "As far as I can tell, this is not true. However it is worth digging into the details around performance. The maximum update rate will limit how fast you can turn your stepper motors and thus the speed of the machine. It's said the maximum update rate is 5kHz, which is usable."

For software, audioartillery is using the open-source LinuxCNC. For hardware, a Raspberry Pi 5 — "4GB version is fine," the maker notes — with a Byte2Bot Parallel HAT add-on, a stepper motor breakout board, and driver modules for the CNC's X, Y, and Z axis stepper motors.

The full write-up is available on Instructables; audioartillery has also designed a 3D-printable case for the Raspberry Pi 5 to make active cooling easier, but at the time of writing had yet to release the print files.