ADXL345传感器外观

ADXL345传感器介绍

• ADXL345三轴加速度采用ADXL345芯片，具有体积小，功耗低的特点，
• 13位数字精度分辨能够测量超过±16g的加速度变换。
• 信号输出为16位数字输出，可以通过SPI与I2C接口实现信号采集。
• ADXL345适用于倾斜角度测量，能够进行静态重力加速度检测。同时也适用于运动状态的追踪，测量运动或冲击过程造成的瞬时加速度。其高分辨率(4mg/LSB)使之能够感应变化小于1°的倾斜角度。
• DFrobot的ADXL345三轴加速度计还内置一款LDO模块让你的加速度计能够工作于3.3~6v的工作电压之下。
• 传感器提供了几个特殊的功能。能够在静态或动态情况下检测是否有运动或停止出现，另外能够感知单轴的加速度值是否超出用户的设定值。检测单击/双击。如果该设备正在下降，能进行自由落体感应检测。这些功能能够被映射到两个中断输出引脚上。
• 在低功耗模式是用户能够基于ADXL345动作感应，进行电源管理，同时只损耗极低的功耗。

ADXL345传感器参数

• 工作电压：3.3~6v
• 超低功耗：测量模式下40uA电流损耗，待机模式下0.1uA@2.5v
• 通讯接口：I2C、SPI(3线or4线)
• 接口类型：0.1″插针孔
• 尺寸：20x15mm

电路连接图

ADXL345和Arduino引脚对应列表

• 该连线方式适用于ADXL345的IIC通讯方式与Uno的通讯。如果您使用其他控制板，IIC管脚可能有所不同，请查阅对应管脚确保连线正确。如需使用ADXL345的SPI通讯模式，请查阅其数据手册

测试代码

该代码是用来收集传感器三轴加速度值，并计算Roll及Pitch角度信息。

#include 

#define DEVICE (0x53)      //ADXL345 device address
#define TO_READ (6)        //num of bytes we are going to read each time (two bytes for each axis)

byte buff[TO_READ] ;        //6 bytes buffer for saving data read from the device
char str[512];              //string buffer to transform data before sending it to the serial port
int regAddress = 0x32;      //first axis-acceleration-data register on the ADXL345
int x, y, z;                        //three axis acceleration data
double roll = 0.00, pitch = 0.00;       //Roll & Pitch are the angles which rotate by the axis X and y 
//in the sequence of R(x-y-z),more info visit
// https://www.dfrobot.com/wiki/index.php?title=How_to_Use_a_Three-Axis_Accelerometer_for_Tilt_Sensing#Introduction

void setup() {
  Wire.begin();         // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output

  //Turning on the ADXL345
  writeTo(DEVICE, 0x2D, 0);      
  writeTo(DEVICE, 0x2D, 16);
  writeTo(DEVICE, 0x2D, 8);
}

void loop() {

  readFrom(DEVICE, regAddress, TO_READ, buff); //read the acceleration data from the ADXL345
                                              //each axis reading comes in 10 bit resolution, ie 2 bytes.  Least Significat Byte first!!
                                              //thus we are converting both bytes in to one int
  x = (((int)buff[1]) << 8) | buff[0];   
  y = (((int)buff[3])<< 8) | buff[2];
  z = (((int)buff[5]) << 8) | buff[4];

  //we send the x y z values as a string to the serial port
  Serial.print("The acceleration info of x, y, z are:");
  sprintf(str, "%d %d %d", x, y, z);  
  Serial.print(str);
  Serial.write(10);
  //Roll & Pitch calculate
  RP_calculate();
  Serial.print("Roll:"); Serial.println( roll ); 
  Serial.print("Pitch:"); Serial.println( pitch );
  Serial.println("");
  //It appears that delay is needed in order not to clog the port
  delay(50);
}

//---------------- Functions
//Writes val to address register on device
void writeTo(int device, byte address, byte val) {
  Wire.beginTransmission(device); //start transmission to device 
  Wire.write(address);        // send register address
  Wire.write(val);        // send value to write
  Wire.endTransmission(); //end transmission
}

//reads num bytes starting from address register on device in to buff array
void readFrom(int device, byte address, int num, byte buff[]) {
  Wire.beginTransmission(device); //start transmission to device 
  Wire.write(address);        //sends address to read from
  Wire.endTransmission(); //end transmission

    Wire.beginTransmission(device); //start transmission to device
  Wire.requestFrom(device, num);    // request 6 bytes from device

  int i = 0;
  while(Wire.available())    //device may send less than requested (abnormal)
  { 
    buff[i] = Wire.read(); // receive a byte
    i++;
  }
  Wire.endTransmission(); //end transmission
}

//calculate the Roll&Pitch
void RP_calculate(){
  double x_Buff = float(x);
  double y_Buff = float(y);
  double z_Buff = float(z);
  roll = atan2(y_Buff , z_Buff) * 57.3;
  pitch = atan2((- x_Buff) , sqrt(y_Buff * y_Buff + z_Buff * z_Buff)) * 57.3;
}

• 常用的三轴加速度传感器数据处理的方法：How to Use a Three-Axis Accelerometer for Tilt Sensing.

测试效果

打开串口监视窗口，可以看到类似下图的数据，分别为：三轴加速度的数据，按照R-xyz旋转顺序时的Roll及Pitch角度。按各轴旋转可以观测到相应的数据变化。

应用

• 单击/双击检测
• 自由落体检测
• 倾角测量
• 切换横屏/竖屏模式

本文整理于DFRobot wiki