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Materials
Circuit
1. Breadboard power (Vcc) to 1K-ohm resistor.
2. 1K-ohm resistor to photoresistor power.
3. Photoresistor ground to breadboard ground.
4. Wire from between resistor & photoresistor to PIC pin AN0.
If R1 is the photoresistor, the voltage will increase with
increasing light intensity. If R2 is the photoresistor, the
voltage will decrease with increasing light intensity.
Code for single photoresistor
//all these # below set
up the PIC
#include <16F877A.h>
#device adc=8
#FUSES NOWDT
//No Watch Dog Timer
#FUSES HS
//Highspeed Osc > 4mhz
#FUSES PUT
//Power Up Timer
#FUSES NOPROTECT //Code not protected from reading
#FUSES NODEBUG //No Debug
mode for ICD
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP
//No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOCPD
//No EE protection
#use delay(clock=20000000) //crystal oscillator at 20000000
hertz
#use rs232(baud=9600, xmit=PIN_C6, invert) //serial port output
pin & baud rate
//run photoresistor signal wire to pin AN0
//connect LED/resistor to pin RB7
void main(){
int16 photo=0; //16 bit integer, safer than using int because
//int is only 8 bit which might lead to overflow problems for
add, multiply
setup_adc(ADC_CLOCK_INTERNAL); //configure analog to digiral
converter
setup_adc_ports(ALL_ANALOG); //set pins AN0-AN7 to analog (can
read values from 0-255 instead of just 0,1)
while(true){ //loop forever
set_adc_channel(0);//set the pic to read from AN0
delay_us(20);//delay 20 microseconds to allow PIC to switch to
analog channel 0
photo=read_adc(); //read input from pin AN0: 0<=photo<=255
//turn on LED when input > 127, else turn off LED
//Put finger over photoresistor & take it off to see LED turn
on/off
//127 may not be the actual value that separates light from
dark, so try different values
if(photo > 127){
output_high(PIN_B7);
}
else{
output_low(PIN_B7);
}
}
}
Code for multiple photoresistors
//all these # below set
up the PIC
#include <16F877A.h>
#device adc=8
#FUSES NOWDT //No Watch Dog
Timer
#FUSES HS
//Highspeed Osc > 4mhz
#FUSES PUT
//Power Up Timer
#FUSES NOPROTECT //Code not protected from reading
#FUSES NODEBUG //No Debug mode for ICD
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP //No low voltage
prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOCPD //No EE protection
#use delay(clock=20000000) //crystal oscillator at 20000000
hertz
#use rs232(baud=9600, xmit=PIN_C6, invert) //serial port output
pin & baud rate
//read input from 3 photoresistors
//run photoresistor signal wires to pin AN0, AN1, AN2
void main(){
int16 photo0=0; //16 bit integer, safer than using int
//int is only 8 bit which might lead to overflow problems for
add, multiply
int16 photo1=0;
int16 photo2=0;
setup_adc(ADC_CLOCK_INTERNAL); //configure analog to digiral
converter
setup_adc_ports(ALL_ANALOG); //set pins AN0-AN7 to analog (can
read values from 0-255 instead of just 0,1)
while(true){ //loop forever
set_adc_channel(0);//set the pic to read from AN0
delay_us(20);//delay 20 microseconds to allow PIC to switch to analog
channel 0
photo0=read_adc(); //read input from pin AN0: 0<=photo<=255
set_adc_channel(1);//set the pic to read from AN1
delay_us(20);
photo1=read_adc();
set_adc_channel(2); //set the pic to read from AN2
delay_us(20);
photo2 = read_adc();
//You could add 3 LEDs and turn them on if photo0/1/2 > 127
//just as with code for single photoresistor
}
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