AstralCNC • StarCNC Retrofit

Our high school shop had a 25-year-old Larken 24/24 CNC router sitting dormant because its original Windows 98 parallel-port controller died. The mechanical 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 bring the machine back to life.

Key Engineering Decisions

• Hardware-Level E-Stop Latch: High-power AC spindles and stepper coils dump massive electromagnetic interference (EMI) into surrounding wiring. If a microcontroller ever hung from noise, software-based safety stops could fail. I designed a physical hardware latching circuit that cuts stepper driver enable lines directly without relying on MCU firmware.
• Robust 5V Step/Dir Buffering: Driven by 74HC244 line buffers to output crisp 5V logic pulses over long lead wires to industrial external stepper drivers (such as DM542s) without signal degradation.
• Integrated Power Delivery: Onboard AP63357 buck converter steps down the machine's 24V/36V main power supply to clean 5V and 3.3V rails with TVS transient suppression.

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.