Accelerometer
Reports acceleration on each measured axis as a digital value (typically over I²C/SPI) or analog voltage. Static tilt is read from the gravity component; dynamic motion is read from the changing component.
Most modern accelerometers are MEMS capacitive: a silicon proof mass is suspended on tiny springs between fixed electrodes. Acceleration deflects the mass, changing the capacitance, which is sensed and digitized on-chip.
In plain terms
A tiny ball-and-spring inside a box: shake the box and the ball lags behind, stretching the spring. Measure the stretch and you know how hard the box is being shaken.
Why designers use it
- Detect orientation (portrait vs landscape) on phones and tablets.
- Trigger airbag deployment in vehicles via crash-pulse detection.
- Step counting and activity recognition on wearables.
- Vibration monitoring on industrial machinery for predictive maintenance.
Best for
- Tilt
- Free-fall
- Vibration
- Step count
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- When you need rotation rate — that's a gyroscope's job.
- When you need absolute heading — accelerometers can find tilt-aligned 'down', not 'north'.
Common mistakes
- Forgetting to calibrate offset — every chip has a few mg of zero-g bias.
- Reading the data rate too slowly to capture the event of interest (aliasing).
Where you will find it
- Apple Watch crash detection uses the on-board accelerometer (alongside the gyroscope and barometer) to recognize the high-g signature of a car crash.
- Fitbit step counters integrate accelerometer data to count gait cycles.
- Automotive airbag ECUs trigger deployment within 15–30 ms of the accelerometer crossing a calibrated threshold.
A short history
Capacitive MEMS accelerometers were commercialized by Analog Devices in 1991 with the ADXL50 — the first single-chip accelerometer integrating sensor and signal conditioning, originally for automotive airbag systems. The technology grew out of work on micromachined silicon at UC Berkeley and Bell Labs through the 1980s.