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Testing

What the First Printed StackCalc Prototype Can Teach Us

The first useful prototype is rarely the one that looks closest to a product. It is the one that makes the next decision cheaper. The current StackCalc hardware is a 3D-printed, tool-free mechanical prototype. Its KiCad PCB design is complete and fabrication is in progress, but there is no assembled, powered StackCalc board yet. The print lets us ask clearly: does the insertion path make sense, where does a part bind, and which keypad assumptions should be tested next?

Fuzzing the Firmware Path in an RP2350 Emulator

The StackCalc calculator board is not assembled yet, but the firmware path is already rich enough to break in interesting ways. A random input sequence can cross number entry, ENTER, stack lift, shifts, menus, modes, clear, correction, and display updates in combinations that a hand-written demo never reaches.

We use the RP2350 emulator to run the firmware image and fuzz those combinations through its keypad contract. That is firmware-emulation evidence, not evidence of a physical switch matrix or display.

What the Firmware Simulator Can Tell Us Before Board Bring-Up

The current StackCalc prototype is a 3D-printed, tool-free mechanical assembly. Its RP2350 calculator PCB design is in fabrication, but no board has yet been assembled and powered, so we cannot yet make claims about powered bring-up, battery life, display behavior, or key feel on the finished electronics.

That is why the firmware simulator is useful. It gives us a fast way to exercise the calculator software and its proposed row-and-column interface while the physical electronics are still being developed. It is evidence about the simulated build, not evidence that a physical PCB works.