Arduino and LDR example

In this example we show how you connect a photoresistor to an Arduino, the value read from the photoresistor corresponds to the amount of light present. The photoresistor is connected to analog pin 0 in this example.

A practical example could be a dark room sensor for photography, if the reading approached a critical level an alarm could be activated or even a night light

Here is our sensor, its part of the 37 in 1 sensor kit I mentioned in another post.

Schematic

Code

In this example we simply output the reading via the serial port. You can monitor this in the Serial Port Monitor

int sensorValue;

void setup()
{
Serial.begin(9600); // starts the serial port at 9600
}

void loop()
{
sensorValue = analogRead(0); // read analog input pin 0
Serial.print(sensorValue, DEC); // prints the value read
Serial.print(” \n”); // prints a space between the numbers
delay(1000); // wait 100ms for next reading
}

 

In this example we check the value returned by the photoresistor, if it drops beneath a certain value we switch the onboard LED on, if it goes above this value the LED will switch off

int sensorValue;
int led = 13;

void setup()
{
pinMode(led, OUTPUT);
}

void loop()
{
sensorValue = analogRead(0); // read analog input pin 0
//daylight was 700 – so lets detect a reading under 300
if (sensorValue < 300)
{
digitalWrite(led, HIGH);
}
else
{
digitalWrite(led, LOW);
}
delay(1000); // wait 100ms for next reading
}

Links

You can just buy some photoresistors, they are cheap items
Photoresistors on Amazon US

Photoresistors on Amazon UK

Here are links to the sensor kit

Ultimate 37 in 1 Sensor Modules Kit for Arduino from Amazon UK
Ultimate 37 in 1 Sensor Modules Kit for Arduino from Amazon US