# Laser Head Sensor with micro:bit

Difficulty
Moderate
Steps
16

A laser head sensor module is one of many useful external components that you can connect to your micro:bit!

In this guide, you will learn to connect the micro:bit with a laser head sensor module and create your own tripwire alarm system. With the addition of a light dependent resistor, the alarm will start to sound when the laser is broken.

By finishing this guide, you will have created a simple tripwire alarm system.

Parts Used in This Guide

## Step 1  The Module

Let's take a closer look at the laser head sensor module.

It has three pins:

• GND: Though it is labelled '-' on the module, this is the the 'GND' pin. 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.
• Note: Voltage is the difference in electric potential between two points. As it is difficult to talk about voltage without a reference point, we need another point to compare it to.
• Middle Pin: No connection required here
• Signal: This pin is the signal pin, which is the input to control the module

## Step 12  Code for button A and B!

Now that we have connected the laser head module to the micro:bit, we will program it! We will use the two push buttons on the micro-bit to turn the laser on and off.

• Open up MakeCode editor
• Click on the 'Projects' button then click on 'New Project ...'
• From the 'Input' tab, grab two 'on button A pressed' blocks.
• Then click on the 'Pins' tab to grab two 'digital write pin' blocks.
• Arrange them so that:
• When button A is pressed, pin 2  is set to a value of 0.
• When button B is pressed, pin 2 is set to a value of 1.

Upload this code to the micro:bit and press button A and B to see what it does!

Note: These are the two buttons found on the micro:bit.

## Step 13  Add the code for the buzzer!

We have also added a light dependent resistor module and a buzzer module to the circuit. Let's use them!

• Pin 2 has been used to connect to signal (S) of the laser head module, while pin 0 is connected to input or output signal (I/O) of the buzzer module.
• If sensorVal is more than 600, the micro:bit will display the value and then sound the alarm by playing a Middle C tone for 2 beats each time.
• Else, the micro:bit will display the sensorVal when the laser is not broken.

## Step 14  Add Some Visuals!

Let's change the code some more to add more visuals. The changes made:

• When the trip wire alarm system goes off now, it will display an angry face using the micro:bit's LEDs.
• Otherwise, if all is well, it will display a smiley face on the LEDs.

## Step 15  Send a message to a second micro:bit!

If you have another micro:bit laying around, use the following MakeCode, else skip to the next step!

• We will use another micro:bit to receive a message when the trip wire alarm system goes off.
• Now when the laser is broken and the sensorVal goes above 600, the second micro:bit will display the string, "Intruder alert!".