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Micro:bit, Coding Alex Micro:bit, Coding Alex

Micro:bit light sensor basics

The Micro:bit has LEDs that emit light. The same LEDs are used to collect and measure light. The LEDs on the Micro:bit perform double duty.

In this lesson, we are going to:

1. Learn to measure the light received by the sensor.

2. Set the brightness of the Micro:bit LEDs based on the ambient light.

3. Turn the LEDs On or Off based on the ambient light.

Micro:bit light sensor basics

Micro:bit light sensor

The Micro:bit has LEDs that emit light. The same LEDs are used to collect and measure light. The LEDs on the Micro:bit perform double duty.

In this lesson, we are going to:

1. Learn to measure the light received by the sensor.

2. Set the brightness of the Micro:bit LEDs based on the ambient light.

3. Turn the LEDs On or Off based on the ambient light.

You don’t need to have a Micro:bit to learn about the Micro:bit. Microsoft provides a free online Micro:bit simulator. No login account is required. Use the link below to access the simulator.

The simulator is also the environment we use to create code for the Micro:bit.

https://makecode.microbit.org

Use the link to go to the Make Code website. Click the New Project button.

new project button

Use “light sensor project” for the name and click the Create button.

project name

Each new project includes two code blocks. The [on start] code runs instructions the moment the Micro:bit is turned on or restarted. The [forever] loop runs code in the loop for as long as the Micro:bit is powered.

on start and forever code blocks

A BIT of information

A bit is the smallest container of information. A bit holds a maximum of two values, either 1 or 0. These represent programmings states like yes, no, on, off, true or false. The states are translated into information. The combination of possible states is expressed as an exponent. Eight bits is 2 to the power of 8 or 256 bits of information. The number of bits here is exactly what the Micro:bit uses to represent the amount of light received by the sensors. The Micro:bit detects light with the LED sensors. The light is processed and the intensity of the light is converted to a number range. That range is 0 to 255.

Measuring light

Go to the Basic code blocks section. Find the [show information] code block.

basic codes section

Place the code block into the [forever] loop.

show number code block

Go to the Input section; find the [light level] code block.

light level code block

Place the code into the [show number] parameter.

code in parameter

Look over at the simulator. A simulated light meter is placed at the top left corner. The LEDs on the Micro:bit scroll to display the light reading. The light reading is also represented below the light meter. That reading is 128. This number represents the midpoint of the possible light received by the sensors.

Micro:bit simulator

Use the mouse arrow to change the light level. Click inside the meter and move the pointer up. This reduces the light intensity. I reduced the light intensity to 98 in my example. Drag the meter down to increase the light intensity.

light meter value at 98

Dimming

Let’s use the sensor as a dimmer. A dimmer reduces or increases the light based on sensor input.

Remove the [show number] block and set it to one side.

code removed

Go to the Basic section; get a [show icon] code block and place it in the loop.

show icon code in loop

Go to the LED section and into the More section. Find the [set brightness] code block.

set brightness code block

Place the code into the loop and below the [show icon] code block.

code in loop

Get a [light level] code block from the Input section and place it into the [set brightness] parameter.

code in parameter

Go over to the simulator. Move the light input meter up and down. Watch the icon increase and decrease in brightness.

full brightness level

The brightness of the LEDs is proportional to the light level received from the sensor. The sensor provides graduated information to the program. The program uses this information to brighten or dim the LEDs accordingly.

On/Off sensor

The sensor can be used as a simple switch. We need to use conditions to decide when to turn the LEDs On or Off. We want the LEDs to turn on when the light level on the meter is below a certain value. We can choose any value.

Remove the [set brightness] block from the loop and set it to one side.

code block removed

Go to the Logic section and find the [if True then] code block.

code block selected

Place the condition statement inside the loop and below the [show icon] code.

code block attached

The condition statement looks for a condition to be True.

We want the condition statement to look at the light level information. If the value from the meter is less than a certain value, we the LEDs to turn on. If the value is greater than a certain value we want to turn the LEDs Off. We can choose any value to trigger the switch.

We need a way to store this value and pass it into the condition and parameters later. The value will be stored in a Variable.

Go to the Variables section and click the "Make a Variable" button.

make variable button

Set the name of the variable to “light trigger” and click the OK button.

variable name

Variable code blocks are created. Get the [set variable to…] code block.

set variable code block

Place the code block into the [on start] section. You might need to move the code blocks around.

code in on start code block

Enter 100 into the variable parameter. This assigns 100 to the variable. The value is assigned when the Micro:bit turns on or is restarted.

This is our value to turn the LEDs On or Off.

variable parameter changed

Go to the Logic section and into the Comparison blocks. Look for the [less than] cod block.

less than code block selected

Place the code block into the condition parameter.

less than code block in place

Get the [light trigger] variable and place it into the right side of the [less than] parameter.

light trigger variable in place

Get the [light level] input and place it into the left side of the [less than] parameter.

light level in parameter

Get the [set brightness] code block we set aside earlier and place it into the condition statement.

adding code block

Remove the [light level] code from the [set brightness] parameter.

removing code

Take the code to the Codes section to remove it from the coding area.

removing code

If the light level is less than the light trigger, 100, we want the LEDs to turn On. The brightness value is already set at 255. This is the maximum brightness. This takes care of turning the LEDs On.

brightness parameter value

We need to follow the same process for turning the LEDs Off. The process is just reversed. The condition statement turns the LEDs Off when the light level is greater than the light trigger.

Right-click on the condition statement; select the duplicate option.

duplicate option

Place the duplicate below the first condition statement.

code in place

Click the comparator selector; choose the greater than comparator option.

selected operation

Change the brightness level to 0.

brightness level set

Move the light sensor meter to a value less than 100; the icon lights to full brightness.

adjusting brightness

Move the meter to a value greater than 100; the icon turns off.

brightness meter

The light trigger might be too high or low. Change the value in the light trigger variable to 50 or 150. Choose a value of your own.

light trigger variable set to 50
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