Controlling a Photocell with Arduino

Gloria Julien

4 min readJun 10, 2019

Learning how to code an Arduino board

This documentation is part of my studies in the course, SDEG-600–1.

Part 1: Smart Lighting Code

https://openhomeautomation.net/smart-lighting-arduino-photocell/

Hardware Configuration

You first have to plug in the LED. Just connect a wire from the Arduino pin number 2 to the 470 ohms resistor, then to the anode of the LED (the long part), then another wire from the cathode to the ground.

I used 2ea of 220Ω resistors instead of the suggested 470Ω resistor for this circuit. Then, put the two 220Ω resistors in series to simulate a 440Ω resistance across the circuit.

Test Photocell Code:

// Define analog pin
int sensorPin = 0;// Setup
void setup() {
 // Init serial
 Serial.begin(9600);
}// Main loop
void loop() {// Get temperature
 int sensorValue = analogRead(sensorPin);// Put temperature on the serial port
 Serial.println(sensorValue,DEC);// Wait for 1 sec
 delay(1000);
}

Low lighting is around 300 and less.
High lighting is around 600 and above.

Turn LED On/Off Code:

// Pins
int sensorPin = 0;
int lightPin = 2;// Variables
int lightState = 0;
int lowThreshold = 300;
int highTreshold = 600;void setup() {
  
  // Start Serial & set pin to output  
  Serial.begin(9600);
  pinMode(lightPin,OUTPUT);
  
}void loop() {// Read the sensor pin
  int sensorValue = analogRead(sensorPin);// If light level is low is detected, switch light on
  if (sensorValue < lowThreshold){
    digitalWrite(lightPin, HIGH);
  }
  
  // If light level goes up again, switch the lights off
  if (sensorValue > highTreshold){ 
    digitalWrite(lightPin, LOW);
  }
}

Part 1, Figure 2 — Test Video of Turning On/Off LED

Part 2: Brighter Lighting when Display is Bright

Helper code from web: https://forum.arduino.cc/index.php?topic=568260.0

Code Test 1: (using analogWrite( ) )

Changed the lightPin location to “PWM 3”
Changed digitalWrite() to analogWrite() https://www.arduino.cc/reference/en/language/functions/analog-io/analogwrite/
Set output value when ambient lighting is above highThreshold to 255 (always ON)
Set output value when ambient light is below lowThreshold to 100 (halfway ON)

// Pins
int sensorPin = 0;
int lightPin = 3;// Variables
int lightState = 0;
int lowThreshold = 300;
int highThreshold = 600;void setup() {
  
  // Start Serial & set pin to output  
  Serial.begin(9600);
  pinMode(lightPin,OUTPUT);
  
}void loop() {// Read the sensor pin
  int sensorValue = analogRead(sensorPin);// If high light is detected, crank up the light slowly
  if (sensorValue > highThreshold){
    analogWrite(lightPin, 255);
  }
  
  // If light level gets dark, crank the light down
  if (sensorValue < lowThreshold){ 
    analogWrite(lightPin, 100);
  }
}

Code Test 2: Creating step in brightness

Write the current sensorValue to start the LED at before continuing with step increase
Set the light value (either moreBright or lessBright) to change when a certain sensorValue is detected
Create a delay between loops to view the dimming or brightening effects

// Pins
int sensorPin = 0;
int lightPin = 3;// Variables
int lightState = 10;
int lowThreshold = 300;
int highThreshold = 600;
int moreBright = 0;
int lessBright = 255;void setup() {
  
  // Start Serial & set pin to output  
  Serial.begin(9600);
  pinMode(lightPin,OUTPUT);
  
}void loop() {// Read the sensor pin
  int sensorValue = analogRead(sensorPin);// If high light is detected, crank up the light slowly
  if (sensorValue > highThreshold){
    analogWrite(lightPin, sensorValue);
    moreBright = moreBright + lightState;
    analogWrite(lightPin, moreBright);
    
  }
  
  // If light level gets dark, crank the light down
  if (sensorValue < lowThreshold){ 
    analogWrite(lightPin, sensorValue);
    lessBright = lessBright - lightState;
    analogWrite(lightPin, lessBright);}
  delay(500);
}

Part 2, Figure 2 — Brighten LED when Environment is Bright

Part 2, Figure 3 — Dim LED when Environment is Dark

Part 3: Create Emergency Flashing Lights when Lights Out

Code: (Use “blink”)

Modified the variables to create an ON and OFF condition
Use the “blink” code as a setup for flashing emergency lights

// Pins
int sensorPin = 0;
int lightPin = 3;// Variables
int lowThreshold = 300;
int highThreshold = 600;
int lightOff = 0;
int lightOn = 255;void setup() {
  
  // Start Serial & set pin to output  
  Serial.begin(9600);
  pinMode(lightPin,OUTPUT);
  
}void loop() {// Read the sensor pin
  int sensorValue = analogRead(sensorPin);// If high light is detected, keep the lights off
  if (sensorValue > highThreshold){
    analogWrite(lightPin, lightOff);
  }
  
  // If light level gets dark, flash the LED light
  if (sensorValue < lowThreshold){ 
    analogWrite(lightPin,lightOn);
    delay(500);
    analogWrite(lightPin,lightOff);
    delay(500);
  }
}