Lesson 5 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 Tutorials 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.

Code

/************************************
* name:Photoresistor
* function: 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.
*********************************************/
//Email: support@sunfounder.com
//Website: www.sunfounder.com const int NbrLEDs = 8;
const int ledPins[] = {5, 6, 7, 8, 9, 10, 11, 12};
const int photocellPin = 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);
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