Photo Cell Sensor

Introduction

Photocells are sensors that allow you to detect light. They are small, inexpensive, low-power, easy to use and don't wear out. For that reason they often appear in toys, gadgets and appliances. They are often referred to as CdS cells (they are made of Cadmium-Sulfide), light-dependent resistors (LDR), and photoresistors.

For most light-sentsitive applications like "is it light or dark out", "is there something in front of the sensor (that would block light)", "is there something interrupting a laser beam" (break-beam sensors), or "which of multiple sensors has the most light hitting it", photocells can be a good choice!

Features

• 2.54mm general interface
• Wide supply voltage range: 3V–30V
• 2.0cm x 2.0cm module
• Application fields widely

Schematic

Specifications

Key specification

Items	Min
PCB Size	2.0cm*2.0cm
Interface	2.54mm pitch pin header
IO structure	SIG,VCC,GND,NC
VCC	3~30V Type:5V
Supply current	0.5~3mA

Photoresistor characteristics

Items	Conditions	Min	Type	Max	Unit
Light Resistance	10lux	8	-	20	kΩ
Dark Resistance	0lux	-	1	-	kΩ
100γ10	-	-	0.6	-	-
Response Time	Rising	-	20	-	s
	Falling	-	30	-	s
Peak Wavelength	-	-	540	-	nm
Ambient Temperature	-	-30	-	+70	°C

Resistance curve

Usage

Hardware

Connect the module to the MCU the 2.54mm pitch pin header, then you can get a voltage value based on the light intensity of the environment.

Using these data, you can make your own application according to your requirement.

Programming

The program below uses the photo cell sensor to control the LED. As the picture shows above, the photo cell sensor is connected to analog port 0 and the LED is connected to port 12.

The resistance of the photoresistor which stands for light value can be calculated based on the voltage obtained through the analog port. Then you can use this data to control the LED or other thing you like.

<syntaxhighlight lang="c">

1. include <math.h>

const int ledPin=12; //Connect the LED Grove module to Pin12, Digital 12 const int thresholdvalue=10; //The treshold for which the LED should turn on. Setting it lower will make it go on at more light, higher for more darkness

void setup() {

 Serial.begin(9600);                //Start the Serial connection
 pinMode(ledPin,OUTPUT);            //Set the LED on Digital 12 as an OUTPUT

} void loop() {

 int sensorValue = analogRead(0);
 float Rsensor;
 Rsensor=(float)(1023-sensorValue)*10/sensorValue;

 if(Rsensor>thresholdvalue)
 {
   digitalWrite(ledPin,HIGH);
 }
 else
 {
 digitalWrite(ledPin,LOW);
 }

 Serial.println(Rsensor,DEC);

}

</syntaxhighlight>