grove_accel.py

#!/usr/bin/python
#
import smbus
import time

bus = smbus.SMBus(2)

# ADXL345 device address
ADXL345_DEVICE = 0x53

# 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=ADXL345_DEVICE):
        self.address = address
        self.set_bandwidth_rate(BW_RATE_100HZ)
        self.set_range(RANGE_2G)
        self.enable_measurement()

    def enable_measurement(self):
        bus.write_byte_data(self.address, POWER_CTL, MEASURE)

    def set_bandwidth_rate(self, rate_flag):
        bus.write_byte_data(self.address, BW_RATE, rate_flag)

    # set the measurement range for 10-bit readings
    def set_range(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 get_axes(self, gforce=False):
        bdata = bus.read_i2c_block_data(self.address, AXES_DATA, 6)

        x = bdata[0] | (bdata[1] << 8)
        if x & (1 << 16 - 1):
            x = x - (1 << 16)

        y = bdata[2] | (bdata[3] << 8)
        if y & (1 << 16 - 1):
            y = y - (1 << 16)

        z = bdata[4] | (bdata[5] << 8)
        if z & (1 << 16 - 1):
            z = z - (1 << 16)

        x = x * SCALE_MULTIPLIER
        y = y * SCALE_MULTIPLIER
        z = z * SCALE_MULTIPLIER

        if not gforce:
            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()

    while True:
        axes = adxl345.get_axes(True)
        print("ADXL345 on address 0x%x:" % adxl345.address)
        print("   x = %.3fG" % (axes['x']))
        print("   y = %.3fG" % (axes['y']))
        print("   z = %.3fG" % (axes['z']))
        time.sleep(2)