ADXL345 accelerometer and LPC1768 example

The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16g. Digital output data is formatted as 16-bit twos complement and is accessible through either a SPI (3- or 4-wire) or I2C digital interface.

The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes less than 1.0°.

Several special sensing functions are provided. Activity and inactivity sensing detect the presence or lack of motion and if the acceleration on any axis exceeds a user-set level. Tap sensing detects single and double taps. Free-fall sensing detects if the device is falling. These functions can be mapped to one of two interrupt output pins. An integrated, patent pending 32-level first in, first out (FIFO) buffer can be used to store data to minimize host processor intervention.

Features

Parts List

Layout

mbed and ADXL345

Code

You will need to import the library from https://os.mbed.com/components/ADXL345-Accelerometer/ and I used the I2C example as well, which you can see below

[codesyntax lang=”cpp”]

#include "ADXL345_I2C.h"

 ADXL345_I2C accelerometer(p28, p27);
 Serial pc(USBTX, USBRX);

 int main() 
 {
       pc.baud(115200);
     int readings[3] = {0, 0, 0};
     
     pc.printf("Starting ADXL345 test...\n");
     wait(.001);
     pc.printf("Device ID is: 0x%02x\n", accelerometer.getDeviceID());
     wait(.001);
    
     // These are here to test whether any of the initialization fails. It will print the failure
    if (accelerometer.setPowerControl(0x00))
    {
         pc.printf("didn't intitialize power control\n"); 
         return 0;  
    }
     //Full resolution, +/-16g, 4mg/LSB.
     wait(.001);
     
     if(accelerometer.setDataFormatControl(0x0B))
     {
        pc.printf("didn't set data format\n");
        return 0;  
     }
     wait(.001);
     
     //3.2kHz data rate.
     if(accelerometer.setDataRate(ADXL345_3200HZ))
     {
        pc.printf("didn't set data rate\n");
        return 0;    
     }
     wait(.001);
     
     //Measurement mode.
     
     if(accelerometer.setPowerControl(MeasurementMode)) 
     {
        pc.printf("didn't set the power control to measurement\n"); 
        return 0;   
     } 
 
     while (1) 
     {
        wait(0.5);
        accelerometer.getOutput(readings);
        pc.printf("%i, %i, %i\r\n", (int16_t)readings[0], (int16_t)readings[1], (int16_t)readings[2]);
     }
 
 }

[/codesyntax]

Testing

Using a terminal program like Teraterm you should see something like this

-320, 226, 164
-254, -8, 94
-12, -168, -70
-172, -210, 60
-76, -38, -162
-198, 322, 130
-42, -254, -8
-126, 228, 0
-140, 70, -92
-342, 66, 46
-122, 156, 158
-78, 148, 204

Links

GY-291 ADXL345 3-Axis Digital Gravity Sensor Acceleration Module IIC/SPI transmission