How the Wii Remote Accelerometer Works (Piezoelectric MEMS)

The Wii Remote uses a 3‑axis MEMS (Micro‑Electro‑Mechanical Systems) accelerometer based on piezoelectric effect (specifically, a capacitive MEMS design by Analog Devices / STMicroelectronics—commonly ADXL330 or similar).

Physics Simplified

1. Proof Mass: A microscopic silicon mass suspended by flexible springs inside the chip.
2. Inertia: When the remote accelerates, the mass lags behind due to inertia, displacing relative to the frame.
3. Capacitive Sensing: The displacement changes the capacitance between the mass and fixed electrodes (not piezoelectric voltage generation—correction: commercial MEMS accelerometers are almost exclusively capacitive, not piezoelectric).
4. Signal Conditioning: On‑chip ASIC converts capacitance delta → voltage → digital value (I²C/SPI).
5. Three Axes: X (left/right), Y (forward/back), Z (up/down). Gravity provides a constant 1g baseline on Z when flat.

Why MEMS Capacitive (Not Piezoelectric)?

• DC Response: Capacitive measures static gravity (tilt). Piezoelectric only responds to *change* (dynamic), drifting at rest.
• Low Power: µA current draw; piezo requires charge amplifiers.
• Integration: CMOS‑compatible fabrication allows ASIC + MEMS on one die.

Sensor Fusion in Games

• Accelerometer alone: Tilt, shake, gross motion. Cannot distinguish rotation from translation.
• + IR Camera (Sensor Bar): Absolute pointing, yaw correction.
• + Wii MotionPlus (Gyroscope): Precise angular rate (roll/pitch/yaw) → 1:1 sword/golf/tennis.

The accelerometer's 10‑bit resolution (~0.01g) and 100Hz sample rate were revolutionary for a $40 controller in 2006.