Visualizing Ambient Light Sensor (OPT3001) Data Using Matplotlib + MSP432 LaunchPad

In general, this is the output response of any sensor on a serial monitor (for example: Arduino) i.e. separated by a new line:
………
4079
4071
4072
4025
4035
4011
4014
4005
………
It would look nice if we can represent this sensor data graphically. Here’s how you can do this in a few steps!

We will be using a MSP432 LaunchPad + BoosterPack (TI BOOSTXL-EDUMKII) to send light sensor (OPT3001) data to PC serially and visualize the data in Matplotlib. A light sensor is a sensor that measures the intensity of visible light.

What you will need:

1. MSP432 LaunchPad
(http://www.ti.com/tool/MSP-EXP432P401R)
2. Educational BoosterPack MKII
(http://www.ti.com/tool/BOOSTXL-EDUMKII)

1. Energia IDE
Download: https://energia.nu/
2. PyCharm
Download: https://www.jetbrains.com/pycharm/

S1. Open Energia IDE.
S2. Select the correct serial port and board.
S3. Energia comes preloaded with the example code for OPT3001.
S4. Upload the below program to the LaunchPad by clicking on the Upload button.

#include <Wire.h>
#include "OPT3001.h"
#define USE_USCI_B1

opt3001 op;
int ledBlue = 37;

void setup()
{
  unsigned int readings = 0;
  
  Serial.begin(115200);
  delay(1000);  
  op.begin(); 
}
void loop()
{
  // Variables
  uint32_t readings;
     
  // Read OPT3001
  readings = op.readResult();  
  Serial.println(readings, DEC); //LUX Readings
  if (readings < 100)
  {
    digitalWrite(ledBlue, HIGH); //TURN ON - Blue Led             
  }
  else if (readings > 100)
  {
    digitalWrite(ledBlue, LOW); //Turn OFF - Blue Led
  }
  delay(500);
}

Before you begin, make sure that the following prerequisites are met:
-> You have installed Python. You can get it from: https://www.python.org/downloads/
-> You are working with PyCharm Community.

I. Creating a Python script in PyCharm

S1. Let’s start our project: if you are on the Welcome screen, click Create New Project. If you have already got a project open, choose File -> New Project.
S2. Select Pure Python -> Location (Specify the directory) -> Project Interpreter: New Virtualenv Environment -> Virtualenv tool -> Create.
S3. Select the project root in the Project tool window, then select File -> New -> Python file -> Type the new filename.
S4. PyCharm creates a new Python file and opens it for editing.

II. Install the following packages: PySerial, Numpy and Matplotlib.

S1. PySerial is a Python library which provides support for serial connections over a variety of different devices.
S2. Matplotlib is a plotting library for Python.
S3. NumPy is the fundamental package for scientific computing in Python.

III. To install any package in PyCharm

S1. File -> Settings.
S2. Under Project, select Project Interpreter and click on the “+” icon.
S3. In the search bar, type the package you wish to install and click on Install Package.

#NOTE: Make sure the COM port number and the baud rate is the same as that in the Energia sketch.

import serial
import matplotlib.pyplot as plt
plt.style.use("dark_background")
import numpy as np

#In interactive mode, pyplot functions automatically draw to the screen.
#Interactive mode may also be turned on via matplotlib.pyplot.ion(), and turned off via matplotlib.pyplot.ioff().
plt.ion()

msp432 = serial.Serial('COM4', 115200)  #(port number, baudrate) - create a serial object
i = 0
x0 = []
y0 = []

while True:
    msp432Serial = msp432.readline()
    lightSensorArray = int(msp432Serial)
    x0.append(i)
    y0.append(lightSensorArray)
    i += 1
    plt.xlim(left=max(0, i-20), right=i+20)  #set the x-limits of the current axis
    plt.ylim(0, 12000)  #set the y-limits of the current axis
    plt.yticks(np.arange(0, 12000, step=500))
    
    plt.ylabel('LUX Readings', fontname='Comic Sans MS', color='white', fontsize=14)  #set the label for the y-axis
    plt.title('AMBIENT LIGHT SENSOR DATA', fontname='Comic Sans MS', color='white', fontsize=16)  #set a title
    
    p1, = plt.plot(x0, y0, color='r', linewidth=2, marker='o')  #plot x0 versus y0 - red line
    plt.legend([p1], ['OPT3001'], loc='upper right', frameon=True)  #place legend in upper right corner of the chart

    plt.show()  #display the figure
    plt.pause(.000001)  #pause for interval seconds

Depending on your lighting condition you should start seeing a plot of the sensor’s lux reading.

Normally for bright indoors the lux value can be in the range of 1001-5000 while for pitch black conditions the range can be between 0-10. I have also added a small piece of code in the Energia sketch that turns the blue led on when the lux value falls below 100.

Feel free to play around with the code and note that this approach of visualizing data can be extended to almost any type of sensor reading!

References

Matplotlib:
https://matplotlib.org/

PySerial:
https://pyserial.readthedocs.io/en/latest/shortintro.html

Numpy:
https://numpy.org/devdocs/user/quickstart.html

Understanding and Interpreting Lux Values:
https://docs.microsoft.com/en-us/windows/win32/sensorsapi/understanding-and-interpreting-lux-values

OPT3001 Ambient Light Sensor (ALS):
http://www.ti.com/product/OPT3001