Threshold detection is a fundamental concept in electronics and embedded systems, where a specific condition is monitored, and an action is triggered when a predefined threshold is crossed. This technique is widely used in various applications, such as temperature monitoring, light intensity detection, and motion sensing. In this article, we will explore how to implement threshold detection using an Arduino microcontroller. The focus will be on creating a project that detects when a light level crosses a certain threshold and then activates an LED as an indicator.

Project: In this project, we will create a light-sensitive threshold detection system using an Arduino. The objective is to monitor the ambient light level using a photoresistor (LDR) and turn on an LED when the light level falls below a specified threshold. This project is ideal for applications such as automatic night lights or security systems that respond to changes in lighting conditions.

Components List:

1. Arduino Uno (1)
2. Photoresistor (LDR) (1)
3. 10kΩ Resistor (1)
4. LED (1)
5. 220Ω Resistor (1)
6. Breadboard (1)
7. Jumper Wires (several)

Examples:

// Define the pin connections
const int LDR_PIN = A0; // Photoresistor connected to analog pin A0
const int LED_PIN = 13; // LED connected to digital pin 13

// Define the threshold value
const int THRESHOLD = 500; // Adjust this value based on your environment

void setup() {
  // Initialize the LED pin as an output
  pinMode(LED_PIN, OUTPUT);

  // Initialize serial communication for debugging
  Serial.begin(9600);
}

void loop() {
  // Read the value from the photoresistor
  int lightLevel = analogRead(LDR_PIN);

  // Print the light level to the serial monitor
  Serial.print("Light Level: ");
  Serial.println(lightLevel);

  // Check if the light level is below the threshold
  if (lightLevel < THRESHOLD) {
    // Turn on the LED if the light level is below the threshold
    digitalWrite(LED_PIN, HIGH);
  } else {
    // Turn off the LED if the light level is above the threshold
    digitalWrite(LED_PIN, LOW);
  }

  // Small delay to stabilize the readings
  delay(100);
}

Explanation:

1. Pin Definitions: We define the pins for the photoresistor (LDR_PIN) and the LED (LED_PIN).
2. Threshold Definition: A threshold value (THRESHOLD) is set to determine when the LED should be activated.
3. Setup Function:
   • The LED pin is set as an output using pinMode.
   • Serial communication is initialized for debugging purposes using Serial.begin.
4. Loop Function:
   • The light level is read from the photoresistor using analogRead.
   • The light level is printed to the serial monitor for debugging.
   • A conditional statement checks if the light level is below the threshold.
   • If the light level is below the threshold, the LED is turned on using digitalWrite.
   • If the light level is above the threshold, the LED is turned off.
   • A small delay is added to stabilize the readings.

This project demonstrates a simple yet effective way to implement threshold detection using an Arduino. By adjusting the threshold value, you can customize the sensitivity of the system to suit your specific application.