How to Make a Light Controlled Lamp with Photoresistor?

1.Introduction
 

Sensors or components are ubiquitous in our daily life. For example, some public street lights turn on automatically at night and turn off automatically during the day. These make use of a photosensitive element that senses the intensity of external ambient light. When the outdoor brightness decreases at night, the street lights will automatically turn on. In the daytime, the street lights will automatically turn off. The principle of this is very simple.

In this lesson we will implement the function of this street light.

2.Components Required
 

3.Component Knowledge
 

Photoresistor:

Photosensor is a kind of resistor made by using the photoelectric effect of semiconductor, the resistance value changes with the intensity of the incident light, also known as photoelectric detector. When the surrounding light becomes stronger, the resistance becomes smaller and the analog signal becomes larger. However, when the light becomes weaker, the resistance increases and the analog signal becomes smaller.
 

The commonly used material for making photosensor is cadmium sulfide, in addition to selenium, aluminum sulfide, lead sulfide and bismuth sulfide and so on. These materials have the characteristic that their resistance decreases rapidly under the irradiation of light of a specific wavelength. This is because the carriers generated by the light are involved in the conduction and drift under the action of the applied electric field. The electrons rush to the positive electrode of the power supply, and the holes rush to the negative electrode of the power supply, so that the resistance of the photosensor drops rapidly.
 

Photoresistor is commonly applied in the measurement of light, light control and photovoltaic conversion (convert the change of light into the change of electricity).

Photoresistor is also being widely applied to various light control circuit, such as light control and adjustment, optical switches, etc.

We will start with a relatively simple experiment regarding to photovaristor application.

4.Read the Analog Value
 

We first use a simple code to read the value of the photoresistor, print it in the serial monitor. For wiring, please refer to the following wiring diagram.

/*
Read_the_photosensitive_resistance_analog_value
http//www.keyestudio.com
*/
int photocellpin=A0;// initializes the analog PIN A0 connected to the photoresistor
int val=0;// initializes the variable "val" with a value of 0
void setup()
{
Serial.begin(9600);// sets baudrate to 9600
}
void loop()
{
val=analogRead(photocellpin);// reads the value of the sensor and assigns its value to "val"
Serial.println(val);// displays the value of "val"
delay(200);// waits 0.2 second
}

Upload the code to the Plus Mainboard, wire up and power up, open the serial monitor and set the baud rate to 9600. Then you can read the analog value of photoresistor. When the light intensity around the sensor gets dim, the analog value displayed on the serial monitor will gradually reduce. On the contrary, the analog value will gradually increase.

5.Circuit Diagram and Wiring Diagram
 

Next, we make a light controlled lamp.

6.Code
 

/*
Light Controlled Lamp
http//www.keyestudio.com
*/
int photocellpin=A0;// initializes the analog PIN A0 connected to the photoresistor
int ledpin=11;//  initializes digital PIN 11
int val=0;// initializes the variable "val" with a value of 0
void setup()
{
pinMode(ledpin,OUTPUT);// sets digital PIN 11 to "output"
Serial.begin(9600);// sets baudrate to 9600
}
void loop()
{
val=analogRead(photocellpin);//reads the analog value of the sensor and assigns its value to "val"
Serial.println(val);//displays the value of "val"
analogWrite(ledpin,val/4);//sets brightness (Max:255)
delay(10);// waits 0.01 second
}

7.Result
 

Upload the code to the Plus Mainboard, wire up and power up, open the serial monitor and set the baud rate to 9600.

Then you can read the analog value of photoresistor. When the light intensity around the sensor gets dim, the analog value displayed on the serial monitor will gradually reduce. On the contrary, the analog value will gradually increase.