import RPi.GPIO as GPIO, time

progName="Test_readCD2.py"
print("progName:",progName)
#Purpose: to sense if 2CD photocells "see" Light or Dark
#          using an internal pulldown resistor
#By D@CC on 2023JOct30
# tested with PPin=40 on a Raspberrry Pi400
#Cover the CDs with a thumb to "Make it Dark"
print("always works with 2 CD in series (covering both), ")
print("works with 1 CD sometimes. . . ")
print("from phys pin 38 (with output High).")
print("  to phys pin 40 (as input with PUD_DOWN)")
#PPout=38  #phys pin 38 #GPIO 20  output
#PPin =40  #phys pin 40 #GPIO 21  input
PPin=40
#This also works with PPin = 37 (But not PPin=3 nor 19)
# It probably works with some other adjacent pin pairs
def initCD2(PPin):
    #PPin-2 is PPout  (tested with PPin = 40)
    GPIO.setmode(GPIO.BOARD) #physical Board numbers
    #            GPIO.BMB     BroadCoM numbering eg GPIO #s
    isBadPin= ((PPin-2==1) or (PPin-2==17))  # they are 3v3
    # Ground pins won't work either
    if not isBadPin:
        GPIO.setup(PPin-2,GPIO.OUT)
        print("turn On phys pin:", PPin-2)
        GPIO.output(PPin-2, True)
    #if end
    GPIO.setup(PPin, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
    # on a Raspberry Pi, PullUpDown is a 10k resistor
    # a photoresistor photocell (CD) when  lit is 5k0.
    #                                when dark is 0k0
    return
#def end
def readCD2(PPin):
    #Purpose: to return True if both CDs are covered
    #By: D@CC on 2023JOct30
    #Tested with PPin=40
    reading=GPIO.input(PPin)
    # reading is True if the CD photoCells are Dark
    if reading:                                                                                                                                                                                                    
        state=False
    else:
        state=True
    #if end
    #time.sleep(1)
    return state
#def end
turnOn=initCD2(PPin)
while True:
    if readCD2(PPin):
        print("Dark")
    else:
        print("Light")
    #if end
    time.sleep(1)
#while end
#/Test_readCD2.py