Introduction

Light-dependent resistors are electronic components whose resistance changes with light intensity. They are also called LDRs, photoresistors, or photoconductors. 

In this guide, you will learn to connect a light-dependent resistor to the micro:bit, and measure the relative brightness of the environment.

Complete this guide to learn how to use a light-dependent resistor. They are used in all sorts of light-sensing circuits; For instance, they could be used as a sensor in cameras or automatic lights that come on when it gets dark enough.
    • Before we begin, let's take a closer look at the light-dependent resistor module. It has four pins:

      3.3V  : While 'VCC' stands for Voltage Common Collector, we'll connect the VCC pin to 3.3V on the micro:bit

      GND: In electronics, we define a point in a circuit to be a kind of zero volts or 0V reference point, on which to base all other voltage measurements. This point is called  ground or GND.

      DO: Digital Output 

      AO: Analog Output

    • Voltage is the difference in potential between two points. As it is difficult to talk about voltage without a reference point, we need another point to compare it to. 

  1. let threshold = 0
    let sensorVal = 0
    basic.forever(function () {
        sensorVal = pins.analogReadPin(AnalogPin.P1)
        threshold = 500
        basic.showNumber(sensorVal)
    })
    
    • Open up MakeCode editor and start a new project.

    • Add the following code to the Javascript interface

  2. let threshold = 0
    let sensorVal = 0
    basic.forever(function () {
        sensorVal = pins.analogReadPin(AnalogPin.P1)
        threshold = 400
        basic.showNumber(sensorVal)
        if (sensorVal > threshold) {
            basic.showIcon(IconNames.SmallDiamond)
        } else if (sensorVal <= threshold) {
            basic.showIcon(IconNames.Target)
        }
    })
    
    • Connect your computer to the micro:bit by using a microUSB cable

    • Click on the 'Download' button on the bottom left corner of the MakeCode editor

    • The hex file will be downloaded to your 'Downloads' folder. So open up Finder on a Mac OSX, or in Explorer on Windows and go to your Downloads folder.

    • Drag and drop the downloaded hex file to the 'MICRO:BIT' drive

    • You may want to adjust the threshold level to your liking. Then, test it by covering the light-dependent resistor with your hands. The LED will light up.