accel_data.py

# Distributed with a free-will license.
# Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
# MMA8452Q
# This code is designed to work with the MMA8452Q_I2CS I2C Mini Module available from ControlEverything.com.
# https://www.controleverything.com/content/Accelorometer?sku=MMA8452Q_I2CS#tabs-0-product_tabset-2

import os
import smbus
import time

fname = 'accel_data_out'

try:
    os.unlink(fname)
except:
    print "no previous data file to remove"

# Get I2C bus
bus = smbus.SMBus(1)

# MMA8452Q address, 0x1D(28)
# Select Control register, 0x2A(42)
#		0x00(00)	StandBy mode
bus.write_byte_data(0x1D, 0x2A, 0x00)
# MMA8452Q address, 0x1D(28)
# Select Control register, 0x2A(42)
#		0x01(01)	Active mode
bus.write_byte_data(0x1D, 0x2A, 0x01)
# MMA8452Q address, 0x1D(28)
# Select Configuration register, 0x0E(14)
#		0x00(00)	Set range to +/- 2g
bus.write_byte_data(0x1D, 0x0E, 0x00)

time.sleep(0.5)

i = 0

fout = open(fname, 'w')
fout.write( "time, X, Y, Z\n" )

while i < 6000:  # 1 min runtime

    # MMA8452Q address, 0x1D(28)
    # Read data back from 0x00(0), 7 bytes
    # Status register, X-Axis MSB, X-Axis LSB, Y-Axis MSB, Y-Axis LSB, Z-Axis MSB, Z-Axis LSB
    data = bus.read_i2c_block_data(0x1D, 0x00, 7)

    # Convert the data
    xAccl = (data[1] * 256 + data[2]) / 16
    if xAccl > 2047 :
        xAccl -= 4096

    yAccl = (data[3] * 256 + data[4]) / 16
    if yAccl > 2047 :
        yAccl -= 4096

    zAccl = (data[5] * 256 + data[6]) / 16
    if zAccl > 2047 :
        zAccl -= 4096

    # Output data to screen
    ts = int(round(time.time() * 1000))
#    print ts
#    print "Acceleration in X-Axis : %d" %xAccl
#    print "Acceleration in Y-Axis : %d" %yAccl
#    print "Acceleration in Z-Axis : %d" %zAccl
    fout.write( str(ts) + ", " + str(xAccl) + ", " + str(yAccl) + ", " + str(zAccl) + "\n" )
    time.sleep(0.0086)
    i = i + 1

fout.close()