Laser Triggered Countdown

This is a simple arduino based project that consists of a laser tripwire that, when triggered, will begin a countdown sequence on red, orange and green LEDs. I designed this to be an easy project for someone learning how arduinos work (like me).

This is my first instructable so please bare with me 🙂
(I’ll apologies in advance the picture quality, my phone’s camera isn’t too great)

Let’s Go!

Step 1: Materials

Step 2: Connecting the components

Connect all the components using the diagram as a guide.

The ldr will have one leg hooked up to the arduino’s 5volt and the other connected to the arduino’s ground through the 10k resistor. The ldr will also have one leg connected to analog 0.

All the LEDs are connecting in parallel with their positive terminals connected to the arduino (Red – digital pin 13, Orange – digital pin 12 and green – digital pin 11) and their negative terminals connected to ground through a 150 ohm resistor.

I hope the diagram (Made with Fritzing) explains this better than I have.

Step 3: Programming

First of all we need to calibrate the laser to its surroundings.
Take the now completed circuit to the location that this will be used. Connect the arduino to a laptop or computer and open the arduino software installed on it.

Copy + paste this sketch into the window:

// Laser Calibration

void setup()
{
Serial.begin(9600);
}

void loop()
{
Serial.println(analogRead(0));
}

Upload this to your arduino and open the serial window.
With the serial window open point your laser so it shines directly upon the ldr.
You will notice that the numbers in the serial window rise up to around 900ish. (if this doesn’t happen go back to step 2 and check that all your wiring is correct)
Note down the average number seen and take 50 away from it (mine was around 950 so I ended up with 900)
This number stops the ldr from reacting to the atmospheric light and just the light emitted from the laser.

Now copy and paste the following sketch into the arduino window:

// LASAR TRIGGERED COUNTDOWN

#define Red 13
#define Orange 12
#define Green 11

void setup()

{
pinMode(Red, OUTPUT);
pinMode(Orange, OUTPUT);
pinMode(Green, OUTPUT);
}

void loop()
{

if(analogRead(0) < 900) // Enter the value you got when calibrating here, mine was 900
{
digitalWrite(Red, HIGH); // 5
delay (950);
digitalWrite(Red, LOW);
delay (50);
digitalWrite(Red, HIGH); // 4
delay (950);
digitalWrite(Red, LOW);
delay (50);
digitalWrite(Red, HIGH); // 3
delay (950);
digitalWrite(Red, LOW);
delay (50);
digitalWrite(Red, HIGH); // 2
delay (950);
digitalWrite(Red, LOW);
delay (50);
digitalWrite(Orange, HIGH); // 1
delay (950);
digitalWrite(Orange, LOW);
delay (50);
digitalWrite(Green, HIGH); // GO!
delay (5000);
digitalWrite(Green, LOW);
}

else
{
digitalWrite(Red, LOW);
digitalWrite(Orange, LOW);
digitalWrite(Green, LOW);
}

}

Find the line *if(analogRead(0) < 900)* and replace 900 with your calibration number

For more detail: Laser Triggered Countdown