AstralCNC • StarCNC Retrofit

My high school shop had a 25-year-old Larken 24/24 CNC router sitting dormant because its uses bespoke software. The frame, lead screws, and stepper motors were in perfect condition, but the electronics were completely obsolete. I designed AstralCNC, a custom open-hardware controller PCB based on the Raspberry Pi RP2040/RP2350 to run the open sourced GRBL-HAL firmware.

Key Engineering Decisions

• Hardware-Level E-Stop Latch: If a microcontroller ever hung, software-based safety stops could fail. I designed a physical hardware latching circuit to handle the emergency stop button directly without relying on MCU firmware.
• 5V I/O: Driven by 74HC244 line to output 5V logic pulses to external stepper drivers as the machine operated on 5v while the controller was on 3.3v.
• Integrated Power Delivery: Onboard AP63357 buck converter steps down the machine's 24V/36V main power supply to clean 5V and 3.3V rails.

Real-World Machine Specs

• Microcontroller: RP2040 / RP2350 running grblHAL with USB and serial control.
• Axis Support: Up to 8 step/direction channels with configurable microstepping and hardware pulse rates up to 200 kHz per axis.

Results

The 25-year-old router is now fully operational, cutting polycarbonate panels for our Vex Robotics team and course work. Schematics, gerbers, and BOM are fully open-sourced on GitHub.