Built a contactless ultrasonic distance meter for a national engineering competition (WETI 2026, Gdansk University of Technology).

How it works: ATtiny1616 fires a 40 kHz burst, receives the echo through a 2-stage MCP6002 bandpass amp, and fuses two ranging methods - fast ToF envelope onset (TCB0 counter, 100 ns/tick) + Goertzel phase filter for sub-millimeter refinement. NTC thermistor corrects speed of sound in real time. Between measurements the MCU sleeps in Standby, analog frontend powered down - total idle draw: 0.18 mA.

Results: 2.4 mm RMSE over 35 readings, 10-50 cm range, total BOM cost 43.73 PLN (~11 USD). Pure AVR-GCC on bare registers, no Arduino libs.

Custom 2-layer PCB, 3D-printed enclosure, full LaTeX documentation.