1. David Friedman, Surjo Dutta
MMA8451 Accelerometer
David Friedman, Surjo Dutta

2. MMA8451 - Capabilities 3D acceleration measurements
Tilt/orientation detection
Jolt detection
Pulse detection
bit resolution
99 micro-g noise level

3. Measurement capabilities
Orientation detection
Coarse grained detection of sensor orientation (+/- 30 degree uncertainty)
8 orientations detected:
Portrait
up or down
front or back
Landscape
up and down
Measurement capabilities
Accelerations:
14 bit data for accelerations
Ranges:
+/ g
+/ g
+/ g
Jolt detection

4. Capacitive Accelerometers
Acceleration generates spring motion of the proof mass.
C1 and C2 are no longer equal.
Voltages detected across C1 and C2 change.
Capacitive Accelerometers
MMA8451 is a capacitive accelerometer.
In fact, it has three of them. One for each spatial direction.
Sensing fingers
Spring like structure
Proof mass
Acceleration C1 C2

5. Functionality Factory calibrated, but offsets can be manually set
Can transmit 8 or 14 bit data through the I2C bus, for preference of speed or precision
Auto Wake/Sleep can be triggered by an interrupt (Tap Detection, Orientation Detection and Motion/Freefall)
“Freefall” or “Motion” detection allows the sensor to signal the processor of such an event. Thresholds for either event can be set by the user
In-built tap detection and double tap detection with customizable pulse time width and latency between pulses
Orientation detection, to switch between portrait and landscape
Embedded Low-pass and High-pass filters, for noise reduction or to filter out slower data

6. References