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Internet of Things (IoT) | Training Course ▸ Pysense

Pysense: Measuring acceleration, temperature, ...

Introduction

In this example, we will use a Lopy on a Pysense board to access various sensors such as 3-axis accelerometer, thermometer, barometer, ...

Learning outcomes

You will learn how to:

  • access Pysense sensors for you application of interest using Pycom high-level Python modules
  • dive deep into the Pysense sensor chips registers to address your custom use or to fix existing library [advanced and optional]

Required Components

For this example you will need:

  • a LoPy module on a Pysense board
  • a microUSB cables
  • a development PC

The source code is in the src/pysense directory.

Always update the firmware to the most recent version.

Using Pycom-provided high-level modules

In this lab., we will provide a series of examples:

  • accelerometer src/pysense/acceloremeter
  • measuring ambient light src/pysense/ambient-light
  • measuring temperature and atmospheric pressure src/pysense/temp-bar
  • measuring temperature and humidity src/pysense/temp-hum

Pycom provides a library (a set of Python modules) abstracting the implementation details of sensor chips (as you will see below). This library is already included in labs source code under the lib folder of each example. If you want to download or fetch the last version of this libary, please refer to workflow-and-setup.md

Let's take a look a the src/pysense/acceloremeter first:

from pysense import Pysense
from LIS2HH12 import LIS2HH12
import pycom
import micropython
import machine
import time

py = Pysense()
acc = LIS2HH12(py)
while True:
    print('----------------------------------')
    print('X, Y, Z:', acc.read())
    print('Roll:', acc.roll())
    print('Pitch:', acc.pitch())
    print('Yaw:', acc.yaw())
    time.sleep(1)

You notice that it looks particularly simple and straightforward! That's the power of code abstraction and Python.

Let's go trough each step:

  1. first create a Pysense object which will be used to communicate over the I2C serial bus between the microcontroller and sensor devices (in our specific case the LIS2HH12 accelerometer - refer to the src/pysense/datasheet folder for sensors' documentation).
py = Pysense()

For further information on I2C:

  1. then create a LIS2HH12 object passing the previously created Pysense object as argument. While the Pysense object provides general purpose methods to communicate over the I2C bus, this object will further specify the address of the device (LIS2HH12 sensor) and register addresses of interest to be used to calculate and give access to the 3-axis accelerometer measurements.

acc = LIS2HH12(py)

  1. and simply loop over measurements and readings every second:
while True:
    print('----------------------------------')
    print('X, Y, Z:', acc.read())
    print('Roll:', acc.roll())
    print('Pitch:', acc.pitch())
    print('Yaw:', acc.yaw())
    time.sleep(1)

It's that easy!

But less us be clear, in many real implementation, as soon as you'd like to finetune the setups of your sensor, calibrate or sometimes even fix the firmware provided, you will have to immerse yourself in all the technical details of the chip sensor.

Exercises

  1. Change the color of the LED based on accelerometer measurements (green, orange, red).
  2. When you push the button, the measurements are logged/saved into the /flash/log folder (while LED blinking blue every second) and when you push again logging is stopped and LED's colour is back to green.

Advanced

We have provided two versions of the temperature and pressure example:

  • src/pysense/temp-bar
  • src/pysense/temp-bar-alt

It illustrates the situation referred to earlier when the firmware provided (here MPL3115A2 class in /lib folder) needs to be fixed.

Synchronize and run the first implementation src/pysense/temp-bar and you will notice that measurements do not look correct.

Instead, an alterative to the default implementation is provided under src/pysense/temp-bar-alt folder. Try to grasp the general idea.