It's easy to use the analog accelerometer breakouts with CircuitPython and its built-in analog I/O module. You can read the X, Y, Z accelerometer axis values as simple analog inputs that are converted to acceleration values with simple Python code.
This page will show how to use the ADXL335 with a CircuitPython board like the Feather M0. Remember your CircuitPython board must support and have three analog inputs, so the ESP8266 and small boards like Gemma M0 won't work. Stick with a Feather or Metro M0.
Wire up the ADXL335 to your board as follows:
- Board 3V to sensor VIN
- Board GND to sensor GND
- Board A1 to sensor Xout
- Board A2 to sensor Yout
- Board A3 to sensor Zout
Remember you can use any available analog inputs for the X, Y, Z outputs. Be sure that these analog inputs are tolerant of up to 3.3 volt input (the Feather and Metro M0 powered by 3.3-5V as shown will be tolerant)!
Next connect to the board's serial REPL so you are at the CircuitPython >>> prompt.
If you haven't read it yet it will be helpful to read the analog I/O guide as it explains the basics of reading analog inputs with the board's analog to digital converter. We will read the X, Y, Z axis values as analog inputs. First import the necessary board and analogio modules and create three inputs, one for each axis:
import board import analogio x_axis = analogio.AnalogIn(board.A1) y_axis = analogio.AnalogIn(board.A2) z_axis = analogio.AnalogIn(board.A3)
You can read the raw value of an axis with the value property:
print('Raw XYZ: ({0}, {1}, {2})'.format(x_axis.value, y_axis.value, z_axis.value))
Raw values aren't that interesting though, you really want the acceleration. Luckily it's easy to convert raw values to acceleration with a simple formula. Remember these sensors output a radiometric analog voltage proportional to the acceleration between -3G and 3G. Let's define a function to do this conversion:
def accel_value(axis):
# Convert axis value to float within 0...1 range.
val = axis.value / 65535
# Shift values to true center (0.5).
val -= 0.5
# Convert to gravities.
return val * 3.0
Now try reading the axis values again using the function to convert to gravities:
x = accel_value(x_axis)
y = accel_value(y_axis)
z = accel_value(z_axis)
print('Acceleration (G): ({0}, {1}, {2})'.format(x, y, z))
That's all there is to using the ADXL335 with CircuitPython! You can use the built-in analog input capabilities to convert the accelerometer's X, Y, Z axis acceleration into a gravity value for your own use!
Here's a complete example of printing the X, Y, Z axis acceleration every second. Save this as main.py on your board and examine the REPL output:
import analogio
import board
import time
# Create analog inputs for each ADXL335 axis.
x_axis = analogio.AnalogIn(board.A1)
y_axis = analogio.AnalogIn(board.A2)
z_axis = analogio.AnalogIn(board.A3)
# Define function to convert raw analog values to gravities.
def accel_value(axis):
# Convert axis value to float within 0...1 range.
val = axis.value / 65535
# Shift values to true center (0.5).
val -= 0.5
# Convert to gravities.
return val * 3.0
# Main loop prints acceleration every second.
while True:
x = accel_value(x_axis)
y = accel_value(y_axis)
z = accel_value(z_axis)
print('Acceleration (G): ({0}, {1}, {2})'.format(x, y, z))
time.sleep(1.0)
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