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2.2.1 Photoresistor

Introduction

Photoresistor is a commonly used component of ambient light intensity in life. It helps the controller to recognize day and night and realize light control functions such as night lamp. This project is very similar to potentiometer, and you might think it changing the voltage to sensing light.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
ADC0834	-
Photoresistor	BUY

Schematic Diagram

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/c/2.2.1/

Step 3: Compile the code.

gcc 2.2.1_Photoresistor.c -lwiringPi

Step 4: Run the executable file.

sudo ./a.out

When the code is running, the brightness of the LED will change according to the light intensity sensed by the photoresistor.

Note

If it does not work after running, or there is an error prompt: "wiringPi.h: No such file or directory", please refer to Install and Check the WiringPi.

Code

#include <wiringPi.h>
#include <stdio.h>
#include <softPwm.h>

typedef unsigned char uchar;
typedef unsigned int uint;

#define     ADC_CS    0
#define     ADC_CLK   1
#define     ADC_DIO   2
#define     LedPin    3

uchar get_ADC_Result(uint channel)
{
    uchar i;
    uchar dat1=0, dat2=0;
    int sel = channel > 1 & 1;
    int odd = channel & 1;

    pinMode(ADC_DIO, OUTPUT);
    digitalWrite(ADC_CS, 0);
    // Start bit
    digitalWrite(ADC_CLK,0);
    digitalWrite(ADC_DIO,1);    delayMicroseconds(2);
    digitalWrite(ADC_CLK,1);    delayMicroseconds(2);
    //Single End mode
    digitalWrite(ADC_CLK,0);
    digitalWrite(ADC_DIO,1);    delayMicroseconds(2);
    digitalWrite(ADC_CLK,1);    delayMicroseconds(2);
    // ODD
    digitalWrite(ADC_CLK,0);
    digitalWrite(ADC_DIO,odd);  delayMicroseconds(2);
    digitalWrite(ADC_CLK,1);    delayMicroseconds(2);
    //Select
    digitalWrite(ADC_CLK,0);
    digitalWrite(ADC_DIO,sel);    delayMicroseconds(2);
    digitalWrite(ADC_CLK,1);

    digitalWrite(ADC_DIO,1);    delayMicroseconds(2);
    digitalWrite(ADC_CLK,0);
    digitalWrite(ADC_DIO,1);    delayMicroseconds(2);

    for(i=0;i<8;i++)
    {
        digitalWrite(ADC_CLK,1);    delayMicroseconds(2);
        digitalWrite(ADC_CLK,0);    delayMicroseconds(2);

        pinMode(ADC_DIO, INPUT);
        dat1=dat1<<1 | digitalRead(ADC_DIO);
    }

    for(i=0;i<8;i++)
    {
        dat2 = dat2 | ((uchar)(digitalRead(ADC_DIO))<<i);
        digitalWrite(ADC_CLK,1);    delayMicroseconds(2);
        digitalWrite(ADC_CLK,0);    delayMicroseconds(2);
    }

    digitalWrite(ADC_CS,1);
    pinMode(ADC_DIO, OUTPUT);
    return(dat1==dat2) ? dat1 : 0;
}

int main(void)
{
    uchar analogVal;
    if(wiringPiSetup() == -1){ //when initialize wiring failed,print messageto screen
        printf("setup wiringPi failed !");
        return 1;
    }
    softPwmCreate(LedPin,  0, 100);
    pinMode(ADC_CS,  OUTPUT);
    pinMode(ADC_CLK, OUTPUT);

    while(1){
        analogVal = get_ADC_Result(0);
        printf("Current analogVal : %d\n", analogVal);
        softPwmWrite(LedPin, analogVal);
        delay(100);
    }
    return 0;
}

Code Explanation

The codes here are the same as that in 2.1.4 Potentiometer. If you have any other questions, please check the code explanation of 2.1.7 Potentiometer for details.

Phenomenon Picture