Digital Level

The screen updates around five times a second, which makes the level feel sluggish next to a commercial unit. I'd assumed the bottleneck was I²C transport, but the bus is already at 400 kHz and the renderer only flushes dirty banks, not the full framebuffer — both of those are fine. The real cost is the circle drawing routine. It walks the perimeter in fine angular steps and calls cos() and sin() on every step, four circles per frame between the two clear-and-redraw passes. The ATmega328 has no FPU, so each soft-float trig call is roughly a thousand cycles, and at 8 MHz the trig alone burns about 125 ms per frame — almost exactly the observed 5–7 Hz. The fix is a precomputed unit-circle lookup table in PROGMEM (or a midpoint Bresenham circle), which would drop per-frame cost by two orders of magnitude and push the refresh well past 50 Hz.

The 3D-printed case was sized to fit a 4×AA battery holder alongside the PCB, OLED, and buttons. I forgot to put a channel in it for the battery wires to reach the board. Rather than reprint the whole case I jerry-rigged the wiring after the fact.

This project ran in parallel with my capstone, and a few things got cut when time ran out. Tap-to-wake via the ADXL343 interrupt pin was in the design but never implemented. A tilt-controlled game and a beeper that would chirp as you approached level were both stretch goals that didn't survive. Sleep and low-power modes got disabled entirely rather than tuned, trading battery life for one less thing to debug under deadline.