Accelerometer

Accelerometers

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Accelerometer

  • Measures acceleration
    • Movement
    • Gravity

  • Model: ADXL345

  • Measurement range: ±2g/±4g/±8g/±16g
    • g = 9.8 m/s2 (Earth’s gravity)
  • Uses I2C serial protocol

Uses

  • Tilting sensing
  • Orientation detection (e.g. smart phone)
  • Vibration sensing
  • Motion (e.g. Wiimote)
    • Free fall

Measurement

  • Measures acceleration in X, Y, Z direction
  • At least one direction will be to acceleration due to gravity at any given time. This is how the sensor “knows” what orientation it is in

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  • It can be confusing because there are multiple types of sensors that perform similar functions
  • Other types of sensors are gyroscopes and inertial measuring units

Gyroscopes

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  • Measure rotation in X, Y, Z (pitch, roll, yaw)
  • Useful for flight guidance and autonomous vehicles

IMU (inertial measurement unit)

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  • Combine accelerometer and gyroscope
  • Detailed measurement of orientation, position, and velocity
  • Provides up to nine degrees of freedom
  • Useful for robotics

Sensor Wiring

Sensor Argon Function
GND GND Ground
VCC 3V3 Power (requires 3.3v)
CS 3V3 Need for I2C mode
SDO GND Need for I2C mode
SDA SDA I2C data (no resistors needed)
SCL SCL I2C clock (no resistors needed)
INT1 Any GPIO Pin Optional (if using interrupts)
INT2 Any GPIO Pin Optional (if using interrupts)

Sensor Wiring

ADXL345_Sparkfun_Particle Library

  • Initialize accelerometer object
ADXL345 adxl; 		//accelerometer object

void setup() {
  accel.powerOn(); // Power on the ADXL345
  • There are other additional settings to configure tap, etc.
  • These can be found in the example files in the library

Library Operations

  • Recommended library for Argon
    • ADXL345_Sparkfun_Particle
  • Check for vibrations
    • accel.readTap()
    • true means vibration
  • Measure acceleration
    • accel.cx int value for force of gravity in the X direction

    • accel.cy int value for force of gravity in the Y direction

    • accel.cz int value for force of gravity in the Z direction

Library Operations

adxl.readAndCalcAccel();
float x = adxl.cx;		//get X-dir measurement (in G's)  
float y = adxl.cy;		  
float z = adxl.cz;

Exercise 1

  • Create new project
  • Install library ADXL345_Sparkfun_Particle
  • Test library examples Sparkfun_ADXL345_Graph.ino

Exercise 2

  • Connect RGB LED
  • Then change LED colors based acceleration
  • Then turn on LED if there is vibration
  • Change LED colors based on orientation

Credit

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