Lesson 4 Photoresistor

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Introduction

A photoresistor 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.

Experimental Conditions

– 1 * SunFounder Uno board

– 1 * USB data cable

– 1 * Photoresistor

– 1 * Resistor (10KΩ)

– 8 * LED

– 8 * Resistor (220Ω)

– Jumper wires

– 1 * Breadboard

Experimental Principle

The resistance of the photoresistor changes with incident light intensity. If the incident light intensity is high, the resistance reduces; if low, increases.

In this experiment, we will use eight LEDs to indicate light intensity. The higher the light intensity is, the more the LED is lit. When the light intensity is high enough, all the LEDs will be lit. When there is no light, all the LEDs will go out.

Experimental Procedures

Step 1: Build the circuit

The schematic diagram

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

Step 3: Compile the code

Step 4: Upload the sketch to the SunFounder Uno board

Now, if you shine the photoresistor with a certain light intensity, you will see several LEDs light up. If you increase the light intensity, you will see more LEDs light up. When you place it in dark environment, all the LEDs will go out.

Exploration

In addition, you can replace the photoresistor with a microphone to use LEDs to indicate sound intensity. The higher the sound intensity is, the more LEDs are lit. You can realize this effect by yourself.

Code

//Photoresistor
/*
Turns on a series of LEDs proportional to a value of an analog sensor.
8 LEDs are controlled but you can change the number of LEDs by changing
the value of NbrLEDs and adding the pins to the ledPins array
*/const int NbrLEDs = 8; // 8 leds
const int ledPins[] = { 5, 6, 7, 8, 9, 10, 11, 12 };//8 leds attach to 5,6,7,8,9,10,11,12 respectively
const int photocellPin = A0; //photoresistor attach to A0
int sensorValue = 0; // value read from the sensor
int ledLevel = 0; // sensor value converted into LED ‘bars’void setup()
{
for (int led = 0; led < NbrLEDs; led++)
{
pinMode(ledPins[led], OUTPUT);// make all the LED pins outputs
}
}void loop()
{ sensorValue = analogRead(photocellPin); //read the value of A0
ledLevel = map(sensorValue, 300, 1023, 0, NbrLEDs); // map to the number of LEDs
for (int led = 0; led < NbrLEDs; led++)
{
if (led < ledLevel )
{
digitalWrite(ledPins[led], HIGH); // turn on pins less than the level
}
else
{
digitalWrite(ledPins[led],LOW); // turn off pins higher than
// the level
}
}
}

Video