It's easy to use the MMA8451 sensor with Python or CircuitPython, and the Adafruit CircuitPython MMA8451 module. This module allows you to easily write Python code that reads the acceleration and more from the sensor.
You can use this sensor with any CircuitPython microcontroller board or with a computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library.
CircuitPython Microcontroller Wiring
First wire up a MMA8451 to your board exactly as shown on the previous pages for Arduino using an I2C connection. Here's an example of wiring a Feather M0 to the sensor with I2C:
Python Computer Wiring
Since there's dozens of Linux computers/boards you can use we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported.
Here's the Raspberry Pi wired with I2C:
CircuitPython Installation of MMA8451 Library
Next you'll need to install the Adafruit CircuitPython MMA8451 library on your CircuitPython board.
First make sure you are running the latest version of Adafruit CircuitPython for your board.
Next you'll need to install the necessary libraries to use the hardware--carefully follow the steps to find and install these libraries from Adafruit's CircuitPython library bundle. Our introduction guide has a great page on how to install the library bundle for both express and non-express boards.
Remember for non-express boards like the, you'll need to manually install the necessary libraries from the bundle:
- adafruit_mma8451.mpy
- adafruit_bus_device
Before continuing make sure your board's lib folder or root filesystem has the adafruit_mma8451.mpy, and adafruit_bus_device files and folders copied over.
Next connect to the board's serial REPL so you are at the CircuitPython >>> prompt.
Python Installation of MMA8451 Library
You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!
Once that's done, from your command line run the following command:
sudo pip3 install adafruit-circuitpython-mma8451
If your default Python is version 3 you may need to run 'pip' instead. Just make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!
CircuitPython & Python Usage
To demonstrate the usage of the sensor we'll initialize it and read the acceleration from the board's Python REPL. Run the following code to import the necessary modules and initialize the I2C connection with the sensor:
import board import adafruit_mma8451 i2c = board.I2C() sensor = adafruit_mma8451.MMA8451(i2c)
Now you're ready to read values from the sensor using any of these properties:
- acceleration - This returns a 3-tuple of X, Y, Z acceleration values in meters per second squared (i.e. 9.8m/s^2 is the force of gravity on the surface of the earth).
-
orientation - This is a value the MMA8451 calculates to help you understand what orientation the sensor is in, kind of like how a smartphone detects if its landscape or portrait orientation. This will return one of the following values:
- adafruit_mma8451.PL_PUF: Portrait, up, front
- adafruit_mma8451.PL_PUB: Portrait, up, back
- adafruit_mma8451.PL_PDF: Portrait, down, front
- adafruit_mma8451.PL_PDB: Portrait, down, back
- adafruit_mma8451.PL_LRF: Landscape, right, front
- adafruit_mma8451.PL_LRB: Landscape, right, back
- adafruit_mma8451.PL_LLF: Landscape, left, front
- adafruit_mma8451.PL_LLB: Landscape, left, back
x, y, z = sensor.acceleration
print('Acceleration: x={0:0.3f} m/s^2 y={1:0.3f} m/s^2 z={2:0.3f} m/s^2'.format(x, y, z))
orientation = sensor.orientation
print('Orientation: {0}'.format(orientation))
In addition there are a few properties you can read and write to change the behavior of the sensor:
-
range - The range of the accelerometer measurements. This must be a value of:
- adafruit_mma8451.RANGE_2G: +/- 2G range
- adafruit_mma8451.RANGE_4G: +/- 4G range (the default)
- adafruit_mma8451.RANGE_8G: +/- 8G range
-
data_rate - The rate at which the sensor measures acceleration data. This must be a value of:
- adafruit_mma8451.DATARATE_800HZ: 800hz
- adafruit_mma8451.DATARATE_400HZ: 400hz
- adafruit_mma8451.DATARATE_200HZ: 200hz
- adafruit_mma8451.DATARATE_100HZ: 100hz
- adafruit_mma8451.DATARATE_50HZ: 50hz
- adafruit_mma8451.DATARATE_12_5HZ: 12.5hz
- adafruit_mma8451.DATARATE_6_25HZ: 6.25hz
- adafruit_mma8451.DATARATE_1_56HZ: 1.56hz
sensor.range = adafruit_mma8451.RANGE_8G sensor.data_rate = adafruit_mma8451.DATARATE_400HZ
That's all there is to using the MMA8451 with CircuitPython!
The following is a complete example that will print the orientation and acceleration of the sensor every second. Save this as code.py on your board and open the REPL to see the output.
# SPDX-FileCopyrightText: 2018 Tony DiCola for Adafruit Industries
# SPDX-License-Identifier: MIT
# Simple demo of reading the MMA8451 orientation every second.
import time
import board
import adafruit_mma8451
# Create sensor object, communicating over the board's default I2C bus
i2c = board.I2C() # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C() # For using the built-in STEMMA QT connector on a microcontroller
# Initialize MMA8451 module.
sensor = adafruit_mma8451.MMA8451(i2c)
# Optionally change the address if it's not the default:
# sensor = adafruit_mma8451.MMA8451(i2c, address=0x1C)
# Optionally change the range from its default of +/-4G:
# sensor.range = adafruit_mma8451.RANGE_2G # +/- 2G
# sensor.range = adafruit_mma8451.RANGE_4G # +/- 4G (default)
# sensor.range = adafruit_mma8451.RANGE_8G # +/- 8G
# Optionally change the data rate from its default of 800hz:
# sensor.data_rate = adafruit_mma8451.DATARATE_800HZ # 800Hz (default)
# sensor.data_rate = adafruit_mma8451.DATARATE_400HZ # 400Hz
# sensor.data_rate = adafruit_mma8451.DATARATE_200HZ # 200Hz
# sensor.data_rate = adafruit_mma8451.DATARATE_100HZ # 100Hz
# sensor.data_rate = adafruit_mma8451.DATARATE_50HZ # 50Hz
# sensor.data_rate = adafruit_mma8451.DATARATE_12_5HZ # 12.5Hz
# sensor.data_rate = adafruit_mma8451.DATARATE_6_25HZ # 6.25Hz
# sensor.data_rate = adafruit_mma8451.DATARATE_1_56HZ # 1.56Hz
# Main loop to print the acceleration and orientation every second.
while True:
x, y, z = sensor.acceleration
print(
"Acceleration: x={0:0.3f}m/s^2 y={1:0.3f}m/s^2 z={2:0.3f}m/s^2".format(x, y, z)
)
orientation = sensor.orientation
# Orientation is one of these values:
# - PL_PUF: Portrait, up, front
# - PL_PUB: Portrait, up, back
# - PL_PDF: Portrait, down, front
# - PL_PDB: Portrait, down, back
# - PL_LRF: Landscape, right, front
# - PL_LRB: Landscape, right, back
# - PL_LLF: Landscape, left, front
# - PL_LLB: Landscape, left, back
print("Orientation: ", end="")
if orientation == adafruit_mma8451.PL_PUF:
print("Portrait, up, front")
elif orientation == adafruit_mma8451.PL_PUB:
print("Portrait, up, back")
elif orientation == adafruit_mma8451.PL_PDF:
print("Portrait, down, front")
elif orientation == adafruit_mma8451.PL_PDB:
print("Portrait, down, back")
elif orientation == adafruit_mma8451.PL_LRF:
print("Landscape, right, front")
elif orientation == adafruit_mma8451.PL_LRB:
print("Landscape, right, back")
elif orientation == adafruit_mma8451.PL_LLF:
print("Landscape, left, front")
elif orientation == adafruit_mma8451.PL_LLB:
print("Landscape, left, back")
time.sleep(1.0)
