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Micro:Bit Light Measurement Tutorial

Tutorial Aim:

The aim of this tutorial is to use a BBC micro:bit with a photoresistor (LDR) sensor to measure light levels and display them as a percentage on the micro:bit’s LED screen. By reading the sensor’s analog values, the micro:bit converts light intensity into an easy-to-understand percentage format.

     

Requirements:

This tutorial makes use of the Micro:bit Electronics Learning Package

  • Microsoft MakeCode for micro:bit
  • Micro:bit V2
  • Micro:bit Robot:bit Expansion Shield V2
  • 3 FF Jumper Wires
  • Photoresistor (LDR) Module Sensor Module

Pin Layout:

Micro:Bit Pins:Photoresistor Module Pins:
GNDGND
3.3VVCC
0D0

Setup:

Please refer to the wiring diagram below.

  • Connect the Photoresistor (LDR) Module Sensor Module to pin 0 on the Micro:Bit using the FF jumper wires
  • Open Microsoft Makecode
  • Plug in the Micro:bit to the computer
Click to expand
Click to expand

Code Walk Through:

Calculating the light level:

As the photoresistor’s sensor output is analog, we can calculate the detected light level as a percentage & pause the code so that the percentage can be displayed on the LED grid. The code for this section will go inside the ‘forever’ block.

  • Creating a variable for the sensor output: In the Variables tab select “Make a Variable” & name it “sensorVal”.
  • Reading & storing the sensor output: In the Variables tab select  “set (variable name) to (number), change the variable name to sensorVal & set it to “analog read pin P0” (also found in the Variables tab).
  • Creating a variable for the light level: In the Variables tab select “Make a Variable” & name it lightLevel”
  • Calculating the light level: In the Math tab select -
    1. “0 / 0” & change it to “100 / 1023”
    2. “0 x 0” & drag the previous 2 code lines inside the code snippet so that it becomes “1023 - sensorVal - 100 / 1023”
    3. "0 - 0" & change it to "100 - 0", then drag the previous code snippet to the left hand side so that it becomes "100 - sensorVal x 100 / 1023"
    4. “Round (number)” and set the number to the previous code line
  • Setting lightLevel to the calculation: In the Variables tab select “set (variable name) to (number)” and select the variable to be lightLevel & set it to the math expression we created by dragging it inside the code snippet.
Click to expand
Displaying the percentage:

The code will have to be paused for a specified amount of time so that the micro:bit is able to display the percentage on the LED grid before executing the next task. The code for this section will be inside the ‘forever’ block.

  • Displaying the percentage: In the Basic tab & select “show number (number)” & change it to “show number lightLevel”.
  • Pausing the code: In the Basic tab select “pause (ms)” and set it to 2000 (2 secons).
Click to expand
Flashing the code onto the Micro:Bit:
  • Make sure the Micro:Bit is connected to the computer 
  • On the bottom left corner, click the “Download” button and follow the prompts

Python Code:

Entire python code for the tutorial:

sensorVal = 0
lightLevel = 0

def on_forever():
    global sensorVal, lightLevel
    sensorVal = pins.analog_read_pin(AnalogPin.P0)
    lightLevel = Math.round(100 - sensorVal * (100 / 1023))
    basic.show_number(lightLevel)
    basic.pause(2000)
basic.forever(on_forever)
 

Simulated Light Percentage

Displaying the sensor's output as a percentage for varying levels of brightness

Click to expand

Downloadable Content:

Please find this tutorial's python & hex file for microsoft makecode on our Github.

Credits:

  • Microsoft
  • The Micro:bit Community
  • The STEM Community
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