The Adafruit CLUE has a barometric pressure sensor that uses the pressure readings to calculate altitude. For more information on how this works, check out Wikipedia.
With CircuitPython and a little math, it is possible to use the altitude reading to calculate the height of an object using your CLUE! Start with the CLUE at the bottom of the object, and press button A to set the initial reading, and then lift your CLUE up to the top of the object to get your reading.
Remember that you must have the necessary libraries installed. Verify that your lib folder matches the list found on the CLUE CircuitPython Libraries page before continuing.
To get the most accurate altitude reading, you'll want to find out the sea level pressure at your location. A google search should provide you with a number of options. Make sure you convert the results to hPa. Then set clue.sea_level_pressure = to the sea level pressure at your location in hPa.
Installing Project Code
To use with CircuitPython, you need to first install a few libraries, into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.
Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory examples/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.
Your CIRCUITPY drive should now look similar to the following image:
# SPDX-FileCopyrightText: 2019 Kattni Rembor, written for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""Calculate the height of an object. Press button A to reset initial height and then lift the
CLUE to find the height."""
from adafruit_clue import clue
# Set to the sea level pressure in hPa at your location for the most accurate altitude measurement.
clue.sea_level_pressure = 1015
clue_display = clue.simple_text_display(
text_scale=2,
colors=(clue.CYAN, 0, clue.RED, clue.RED, 0, clue.YELLOW, 0, clue.GREEN),
)
initial_height = clue.altitude
clue_display[0].text = "Calculate height!"
clue_display[2].text = "Press A to reset"
clue_display[3].text = "initial height!"
while True:
if clue.button_a:
initial_height = clue.altitude
clue.pixel.fill(clue.RED)
else:
clue.pixel.fill(0)
clue_display[5].text = "Altitude: {:.1f} m".format(clue.altitude)
clue_display[7].text = "Height: {:.1f} m".format(clue.altitude - initial_height)
clue_display.show()
Let's take a look at the code.
First you set the sea level pressure at your location. Then you set up the text display to prepare to add your lines of text. Note that we don't use every line, so to set the colors on only the lines we used, we include a 0 as the color for the unused lines - this is easier and cleaner than setting them to a color! Then we get an initial height reading. The first three lines of text on the display are not dynamic in any way and can be set outside the loop.
Inside the loop, we check to see if button A is pressed, and if it is, we reset the initial height reading to the current altitude reading. This allows for you to reset the initial height reading while the program is running. As well, we turn the NeoPixel LED on the back of the board red when button A is pressed, otherwise we turn it off. Then we display the current altitude.
This is followed by the current height which is the change in altitude from the initial height reading, which is to say, our simple math: altitude - initial_height.
Then we call show() to make all of it show up on the display.
That's all there is to creating a height calculator with CircuitPython and CLUE!
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