3-Axis tilt sensor for tilt only

[soggycashew]

I have a ADXL345 3-Axis Tilt Sensor working with the below code I found and showing the X,Y and Z in my Thonny shell.

My project is I want to determine what tilt my tractors loader bucket is in so I'm guessing its the X axis for tilt (back, level, down). My question(s) are what if I'm heading uphill with my tractor and the sensor is on my bucket will it take the incline I'm on in consideration and level would be the incline?

2nd question is the print("X:", "{:.2f}".format(acc_x) value displayed in the shell from the below code the degree of angle?

Thanks,

Code: Select all

import machine
from machine import Pin, I2C
import utime
import ustruct

# https://www.digikey.com/en/maker/projects/raspberry-pi-pico-rp2040-i2c-example-with-micropython-and-cc/47d0c922b79342779cdbd4b37b7eb7e2

###############################################################################
# Constants

# I2C address
ADXL345_ADDR = 0x53

# Registers
REG_DEVID = 0x00
REG_POWER_CTL = 0x2D
REG_DATAX0 = 0x32

# Other constants
DEVID = 0xE5
SENSITIVITY_2G = 1.0 / 256  # (g/LSB)
EARTH_GRAVITY = 9.80665     # Earth's gravity in [m/s^2]

###############################################################################

# Initialize I2C with pins 
print("Setting Up i2c")
sda = Pin(0)
scl = Pin(1)
id = 0

# Create I2C object
i2c = I2C(id=id, sda=sda, scl=scl,freq=400000)

# Scan the bus and print out address found
devices = i2c.scan()

if devices:
    for d in devices:
        print("i2c hex:",hex(d))

print("i2c scan:",repr(i2c.scan()))
if 0x53 not in i2c.scan():
    print("Failed to find device")
    raise RuntimeError()

###############################################################################
# Functions

def reg_write(i2c, addr, reg, data):
    """
    Write bytes to the specified register.
    """
    
    # Construct message
    msg = bytearray()
    msg.append(data)
    
    # Write out message to register
    i2c.writeto_mem(addr, reg, msg)
    
def reg_read(i2c, addr, reg, nbytes=1):
    """
    Read byte(s) from specified register. If nbytes > 1, read from consecutive
    registers.
    """
    
    # Check to make sure caller is asking for 1 or more bytes
    if nbytes < 1:
        return bytearray()
    
    # Request data from specified register(s) over I2C
    data = i2c.readfrom_mem(addr, reg, nbytes)
    
    return data

###############################################################################
# Main

# Read device ID to make sure that we can communicate with the ADXL345
data = reg_read(i2c, ADXL345_ADDR, REG_DEVID)
if (data != bytearray((DEVID,))):
    print("ERROR: Could not communicate with ADXL345")
    sys.exit()
    
# Read Power Control register
data = reg_read(i2c, ADXL345_ADDR, REG_POWER_CTL)
print("Power Control Register:", data)

# Tell ADXL345 to start taking measurements by setting Measure bit to high
data = int.from_bytes(data, "big") | (1 << 3)
reg_write(i2c, ADXL345_ADDR, REG_POWER_CTL, data)

# Test: read Power Control register back to make sure Measure bit was set
data = reg_read(i2c, ADXL345_ADDR, REG_POWER_CTL)
print("Register Back Power Control:", data)

# Wait before taking measurements
utime.sleep(2.0)

# Run forever
while True:
    
    # Read X, Y, and Z values from registers (16 bits each)
    data = reg_read(i2c, ADXL345_ADDR, REG_DATAX0, 6)

    # Convert 2 bytes (little-endian) into 16-bit integer (signed)
    acc_x = ustruct.unpack_from("<h", data, 0)[0]
    acc_y = ustruct.unpack_from("<h", data, 2)[0]
    acc_z = ustruct.unpack_from("<h", data, 4)[0]

    # Convert measurements to [m/s^2]
    acc_x = acc_x * SENSITIVITY_2G * EARTH_GRAVITY
    acc_y = acc_y * SENSITIVITY_2G * EARTH_GRAVITY
    acc_z = acc_z * SENSITIVITY_2G * EARTH_GRAVITY

    # Print results
    print("X:", "{:.2f}".format(acc_x), \
          "| Y:", "{:.2f}".format(acc_y), \
          "| Z:", "{:.2f}".format(acc_z))
    
    utime.sleep(0.1)

[elschopi]

Hi,

as far as I understand - if I'm mistaken, please excuse me - your question is, if the sensor would be able to determine if it's on an incline, always giving you only the angle of the loader bucket?
I don't have hands-on experience with these sensors, but from what I understand of their principle of operation, these sensors are not aware of ground level. They measure the relative accelerations in X, Y and Z in respect to the center of gravity, i.e. like a digital sounding line.
Just an idea, you could use a second sensor on the tractor to compare readings and / or create a virtual digital horizon.

Maybe for that use case, using a less advanced sensing method would be less complicated to implement, like a potentiometer for resistive angle measurement of the loader arm?

best regards
Chris