photoresistor_step.py

import RPi.GPIO as GPIO
import time


GPIO.setmode(GPIO.BCM)

pin = 18

def discharge():
    GPIO.setup(pin, GPIO.OUT)
    GPIO.output(pin, False)
    time.sleep(0.1)
    

# return the time taken for the capacitor to go HIGH
# than means around 1.65V
def charge_time():
    t1 = time.time()
    GPIO.setup(pin, GPIO.IN)
    while not GPIO.input(pin):
        # charge for 1ms
        GPIO.setup(pin, GPIO.OUT)
        GPIO.output(pin, True)
        time.sleep(0.001)
        # set to input to test again
        GPIO.setup(pin, GPIO.IN)  
        time.sleep(0.001) 
    t2 = time.time()
    return (t2 - t1) * 1000000

# Take an analog reading as the time taken to charge C
def analog_read():
    discharge()
    return charge_time()


while True:
    print(analog_read())
    time.sleep(0.5)