Sensor 04 Photosensor with digital input

This exercise is based on http://www.ladyada.net/learn/sensors/cds.html

 

Since I tried photosensor with analog input,this tutorial going to explain how to build a circuit and program for photosensor with digital input.

The circuit for photosensor with digital input is same as what we made for Boe-Bot.

 We will use Capacitor and measure the pulses that are sent from it with digital pin.

Actually, if we use analog input for photosensor, it is going to be 5 time easier than do a same thing with digital input. Especially, the program will be more complex. However, it is good to learn.

Requirements

Photosensor

Capacitor(I use a capacitor took out from Boe-Bot)

Wires

Arduino

 

Circuit

Program

This program read a interval of signals that send from capacitor as a darkness of the room.

More detail go http://www.ladyada.net/learn/sensors/cds.html

Basically, photosensor is a variable resistor so that changes the amount of electric supply to a capacitor by the darkness, so that interval of the signal from the capacitor will change. 

int photoPin = 2; // declare valiable 
int val;

void setup(void)
{
Serial.begin(9600); // setup serial speed 
}
void loop(void)
{
val = Reading();  // this cord is very similar with GOSUB that we used in Boe-Bot 
 Serial.println(val);//send back data from Arduino
delay(100);
}

//the following cord is similar with "Subroutine"
int Reading()
{

int time=0;
int pin = 2;
pinMode(pin, OUTPUT); //setup pin . This step is important.
digitalWrite(pin, LOW); //set the pin to ground. This step is also important. 
pinMode(pin,INPUT);//set the pin to read a signal 

while (digitalRead(pin)==0)//make a timer 
{
time++;
if(time==30000)//in case nothing is connected 
{
break;//return to "void loop" 
}
}
return time;//return the value to variable "Reading" 
}