Lesson 17 Photoswitch

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Introduction

The sensor is in fact a photoresistor which changes its resistance with varying light intensity. It can be used to make a photoswitch.

Components

– 1 * SunFounder Uno board

– 1 * USB data cable

– 1 * Relay module

– 1 * Photoresistor sensor module

– 2 * 3-Pin anti-reverse cable

– 1 * Dupont wire (F to F)

Experimental Principle

A photoresistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits. In this experiment, hook up the photoresistor to A0 of the SunFounder board, and relay to pin 8. When the value reaches or even exceeds 400, the normally open contact of the relay is closed and the LED at pin 13 on the SunFounder Uno board will light up; otherwise, it will be off. In this way you can make a photoswitch.

Experimental Procedures

Step 1: Build the circuit

The wiring between the relay and SunFounder Uno board:

RelaySunFounder Uno
GNDGND
VCC5V
SIG8

The wiring between the photoresistor and SunFounder Uno board:  

PhotoresistorSunFounder Uno
SIGA0
VCC5V
SIGA0

Step 2: Program (Please refer to the example code in LEARN -> Get Tutorial on our website)

Step 3: Compile

Step 4: Upload the sketch to SunFounder Uno board

Now hold the photoresistor with your fingers and check the value at A0 on Serial Monitor. You can see when the resistance is up to 400ohm, the normally open contact of the relay is closed and the LED connected to pin 13 on the SunFounder Uno board lights up; or else, it keeps out.

Summary

In this experiment we’ve use the sensor making a photoswitch. You may try other applications. For instance, connect a bulb to the relay module based on the circuit. Then when it gets dimmer, the normally open contact of the relay is closed and the bulb will light up. The same way applies to the street light.

 Code

/*****************************************************
* name:Photoswitch
* function: hold the photoresistor with your fingers and check the value at A0 on Serial Monitor.
* You can see when the resistance is up to 400ohm,
* the normally open contact of the relay is closed and the LED connected to pin 13 on the SunFounder Uno board lights up;
* or else, it keeps out.
************************************************/
//Email:support@sunfounder.com
//website:www.sunfounder.comconst int photocellPin = A0; //photoresistor module attach to A0
const int ledPin = 13; //pin 13 built-in led
const int relayPin=8; //relay module attach to digital 8
int outputValue = 0;
/*************************************************/
void setup()
{
  pinMode(relayPin,OUTPUT); //set relayPin as OUTPUT
  pinMode(ledPin,OUTPUT); //set ledPin as OUTPUT
  Serial.begin(9600); //initialize the serial communication as 9600bps
}
/*************************************************/
void loop()
{
  outputValue = analogRead(photocellPin);//read the value of photoresistor
  Serial.println(outputValue); //print it in serial monitor
  if(outputValue >= 400) //if the value of photoreisitor is greater than 400
  {
    digitalWrite(ledPin,HIGH); //turn on the led
    digitalWrite(relayPin,LOW); //relay connected
  }
  else //else
  {
    digitalWrite(ledPin,LOW); //turn off the led
    digitalWrite(relayPin,HIGH); //and relay disconnected
  }
  delay(1000); //delay 1s
}
/*************************************************/