Raspberry PI and ADXL345 GY-291 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.

Connection

I used the following connection from the module above to my Raspberry PI

PI Connection	Module Connection
3v3	VCC
Gnd	Gnd
SDA	SDA
SCL	SCL

This is a layout showing the connection

Code

This needs the following example – https://github.com/pimoroni/adxl345-python

Copy and extract to a folder on your Raspberry Pi’s file system.

You can run this from the command line by typing in the following sudo python adxl345.py and should see something like the following

Here is the code

Source code

# ADXL345 Python library for Raspberry Pi 
#
# author:  Jonathan Williamson
# license: BSD, see LICENSE.txt included in this package
# 
# This is a Raspberry Pi Python implementation to help you get started with
# the Adafruit Triple Axis ADXL345 breakout board:
# http://shop.pimoroni.com/products/adafruit-triple-axis-accelerometer
 
import smbus
from time import sleep
 
# select the correct i2c bus for this revision of Raspberry Pi
revision = ([l[12:-1] for l in open('/proc/cpuinfo','r').readlines() if l[:8]=="Revision"]+['0000'])[0]
bus = smbus.SMBus(1 if int(revision, 16) >= 4 else 0)
 
# ADXL345 constants
EARTH_GRAVITY_MS2   = 9.80665
SCALE_MULTIPLIER    = 0.004
 
DATA_FORMAT         = 0x31
BW_RATE             = 0x2C
POWER_CTL           = 0x2D
 
BW_RATE_1600HZ      = 0x0F
BW_RATE_800HZ       = 0x0E
BW_RATE_400HZ       = 0x0D
BW_RATE_200HZ       = 0x0C
BW_RATE_100HZ       = 0x0B
BW_RATE_50HZ        = 0x0A
BW_RATE_25HZ        = 0x09
 
RANGE_2G            = 0x00
RANGE_4G            = 0x01
RANGE_8G            = 0x02
RANGE_16G           = 0x03
 
MEASURE             = 0x08
AXES_DATA           = 0x32
 
class ADXL345:
 
    address = None
 
    def __init__(self, address = 0x53):        
        self.address = address
        self.setBandwidthRate(BW_RATE_100HZ)
        self.setRange(RANGE_2G)
        self.enableMeasurement()
 
    def enableMeasurement(self):
        bus.write_byte_data(self.address, POWER_CTL, MEASURE)
 
    def setBandwidthRate(self, rate_flag):
        bus.write_byte_data(self.address, BW_RATE, rate_flag)
 
    # set the measurement range for 10-bit readings
    def setRange(self, range_flag):
        value = bus.read_byte_data(self.address, DATA_FORMAT)
 
        value &= ~0x0F;
        value |= range_flag;  
        value |= 0x08;
 
        bus.write_byte_data(self.address, DATA_FORMAT, value)
 
    # returns the current reading from the sensor for each axis
    #
    # parameter gforce:
    #    False (default): result is returned in m/s^2
    #    True           : result is returned in gs
    def getAxes(self, gforce = False):
        bytes = bus.read_i2c_block_data(self.address, AXES_DATA, 6)
 
        x = bytes[0] | (bytes[1] << 8)
        if(x & (1 << 16 - 1)):
            x = x - (1<<16)
 
        y = bytes[2] | (bytes[3] << 8)
        if(y & (1 << 16 - 1)):
            y = y - (1<<16)
 
        z = bytes[4] | (bytes[5] << 8)
        if(z & (1 << 16 - 1)):
            z = z - (1<<16)
 
        x = x * SCALE_MULTIPLIER 
        y = y * SCALE_MULTIPLIER
        z = z * SCALE_MULTIPLIER
 
        if gforce == False:
            x = x * EARTH_GRAVITY_MS2
            y = y * EARTH_GRAVITY_MS2
            z = z * EARTH_GRAVITY_MS2
 
        x = round(x, 4)
        y = round(y, 4)
        z = round(z, 4)
 
        return {"x": x, "y": y, "z": z}
 
if __name__ == "__main__":
    # if run directly we'll just create an instance of the class and output 
    # the current readings
    adxl345 = ADXL345()
 
    axes = adxl345.getAxes(True)
    print "ADXL345 on address 0x%x:" % (adxl345.address)
    print "   x = %.3fG" % ( axes['x'] )
    print "   y = %.3fG" % ( axes['y'] )
    print "   z = %.3fG" % ( axes['z'] )