How to Connect ADXL345 to Raspberry Pi Pico

In this tutorial learn how to connect the ADXL345 to the Raspberry Pi Pico to get real acceleration values.

Video

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Supplies

ADXL345

Step 1: Physical Connection

Setup pins as follows for I2C connection, you only need 4 jumper wires. You can get the sensor and Raspberry Pi pre-soldered or solder them yourself. This is sufficient enough to start getting sensor values! Be sure not to mix power connections as this can fry the sensor.

Step 2: Code

Run the following code in MicroPython

from machine import Pin, I2C
import time
import ustruct

# Constants
ADXL345_ADDRESS = 0x53 # address for accelerometer 
ADXL345_POWER_CTL = 0x2D # address for power control
ADXL345_DATA_FORMAT = 0x31 # configure data format
ADXL345_DATAX0 = 0x32 # where the x-axis data starts

# Initialize I2C
i2c = I2C(0, sda=Pin(0), scl=Pin(1), freq=400000)

# Initialize ADXL345
def init_adxl345():
    i2c.writeto_mem(ADXL345_ADDRESS, ADXL345_POWER_CTL, bytearray([0x08]))  # Set bit 3 to 1 to enable measurement mode
    i2c.writeto_mem(ADXL345_ADDRESS, ADXL345_DATA_FORMAT, bytearray([0x0B]))  # Set data format to full resolution, +/- 16g

# Read acceleration data
def read_accel_data():
    data = i2c.readfrom_mem(ADXL345_ADDRESS, ADXL345_DATAX0, 6)
    x, y, z = ustruct.unpack('<3h', data)
    return x, y, z

# Main loop
init_adxl345()
while True:
    x, y, z = read_accel_data()
    print('--------------------')
    print(x, y, z) # raw values from sensor
    print("X: {}, Y: {}, Z: {}".format(x*0.0039, y*0.0039, z*0.0039))
    time.sleep(0.5)


# if you do get OSError: [Errno 5] EIO, try unplug and plug
# if you do set different resolution 0.0039 may not be the constant (check data sheet)

If you set everything up properly you should start seeing values in x, y, and z in units of g (9.81 m/s^2).

Some takeaways from the code:

• Gives you acceleration values up to 16g. You can adjust this by changing the bytearray you pass into the DATA_FORMAT register.
• You can calibrate your sensor for more accurate results. ShillehTek has a video on this already here.
• If you do get OSError trying unplugging and plugging the Pico in.
• 0.0039 is retrieved from the ADXL345 datasheet, this value changes depending on the resolution you select
• You can extend this and calculate the angle with some trigonometry, another tutorial will be made on this topic.

Conclusion:

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