Published March 12, 2022 © GPL3+

Light Gate using Arduino

Let's create a light gate using Arduino.

IntermediateShowcase (no instructions)2,806

Things used in this project

Hardware components

Arduino UNO

Photo resistor

I have used KY-018 Photo Resistor Module

Breadboard (generic)

Jumper wires (generic)

LED (generic)

Resistor 330 ohm

Flashlight / Torch

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

Scissor, Electrician

Black Paper Sheet

Story

What is a light gate?

The Light gate is a digital switch-type sensor most commonly used in timing experiments. The Light Gate has an infrared transmitter and receiver that will detect an object passing through the 'gate'.

NOTE: We are going to make a light gate which will detect visible light not infrared light.

The Basic Principle

The light gate we are going to make works on the speed distance time law which is:

Speed = Distance / Time

The distance will be fixed and the time needs to be calculated.

We need a flashlight to emit the light and a photo resistor to collect the light.

The object to measure will be embedded with a breaker (a small piece of paper which will block the light from passing through).

The breaker would have a fixed length (say 4 cm).

When the breaker comes in between the flashlight and photo resistor, the light will be blocked. So we can take the readings of light intensity from the photo resistor and when there is a low reading (which means the light is blocked), we can say that the object is between the flashlight and photo resistor. At that time we will start a timer and wait until the light intensity increases (which means the object is gone). The timer reading will be like 860 ms.

So we can say that the object covered 4 cm (the length of the breaker) in 860 ms (the timer). Then convert the length to meter and time to seconds to get the speed in m/s Through equation we say that:

  Speed = Distance / Time
= Speed = (4 / 100) / (860 / 1000)
= Speed = 0.04 / 0.860
= Speed = 0.05 m/s

Now, lets create the device using Arduino.

1. Paper Cuttings

We need some paper cutting to do the project.

Recommended to use black paper sheet.

A cylindrical cover for the photo resistor.

A paper sheet of length 4 cm (you can use any) to use as breaker.

1 / 3 • The breaker with a length of 4 cm.

2. Hardware

Pin 8 on Arduino to the first leg of resistor.

Resistors second leg to the positive terminal of LED.

LED's negative terminal to GND of Arduino.

Arduino's 5V to - of Photo Resistor.

Arduino's GND to + of Photo Resistor.

Arduino A0 pin to S pin of Photo resistor.

3. Software

Go to code section to get the whole code.

In the code I have given lengthOfBreaker value as 0.04 because the length of the breaker is 4 cm which is 0.04 in meters. You can change it according to the length of your breaker.

4. Testing

Setup the components.

NOTE: The light should only be blocked by the breaker or any other thing with a length of 4 cm. Otherwise the measurement will go wrong!!

Lift up the breadboard and photo resistor so that the object can move below it.

Connect the Arduino UNO to your computer to get the Serial output.

As soon as you turn on the Arduino, you should turn the flashlight on.

Attach the breaker to the object you want to measure the speed.

As soon as the breaker blocks the light the LED turns on and when the object go past the light gate, the LED turns off and the speed will be shown on the Serial Monitor.

Code

Arduino Code

int timer = 0; //For the counting of the breaked time of light.
bool checking = false; //Checks if the the object is being monitored.
float speed = 0; //The final speed of the object.
float lengthOfBreaker = 0.04; //The length of the breaker used in the object.

void setup() {
  pinMode(8, OUTPUT); //An LED for showing the 'checking' variable.
  Serial.begin(9600); //Begin the serial communication.
}

void loop() {
  if (analogRead(A0) < 900) { //Checks if the light intensity is below 900. That means the light is breaked.
    checking = true;
    digitalWrite(8, checking);
    timer = 0;
    while (analogRead(A0) <= 900) { //Increment the timer until the object is gone.
      timer++;
      delay(1); //A fixed time of 1 millisecond is given for counting.
    }
    if (timer > 0) { //Check if the timer value is greater that 0 milliseconds.
      checking = false; //Set the completed variable to true since the checking is completed.
      digitalWrite(8, checking);
      float timeInSec = (float(timer) / float(1000)); //Convert the time in milliseconds to seconds. Output is a float value.
      speed = lengthOfBreaker / timeInSec; //Calculates the speed of the object by using this formula: Speed = Distance / Time
      Serial.print("Object Instantaneous Speed: "); //
      Serial.print(speed);                          //  Print the object speed
      Serial.print(" m/s");                         //  in the Serial monitor.
      Serial.print("\n");                           //
      timeInSec = 0; // Reset the seconds value.
    }
    speed = 0;           //
    checking = false;    //  Reset other values too.
    timer = 0;           //
  }
}

Light Gate using Arduino

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

What is a light gate?

The Basic Principle

1. Paper Cuttings

2. Hardware

3. Software

4. Testing

Schematics

Circuit Diagram

Code

Arduino Code

Credits

madhav133

Comments

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Light Gate using Arduino

Light Gate using Arduino

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

What is a light gate?

The Basic Principle

1. Paper Cuttings

2. Hardware

3. Software

4. Testing

Schematics

Circuit Diagram

Code

Arduino Code

Credits

madhav133

Comments

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