IR_lightgate2

import RPi.GPIO as GPIO
from time import sleep
from datetime import datetime
from decimal import *

#-----------------------------------------------------------#
#                    General Parameters                     #
#-----------------------------------------------------------#

#display no warnings (on command line)
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BOARD)

GPIO.setup(13, GPIO.IN)   # GPIO2, BPW85 phototransistor
GPIO.setup(15, GPIO.IN)   # GPIO3, BPW85 phototransistor

global lg1, lg2, dt1, dt2, distance
lg1 = 0
lg2 = 0

distance = 30000 #um, distance between light gates

#-----------------------------------------------------------#
#function LIGHTGATE: function is executed when input pins   #
#                    are edge triggered                     #
#-----------------------------------------------------------#
def lightgate(channel):

  #Get current date/time stamp
  dt = datetime.now()
  print "Edge triggered on channel ", channel, " at ", dt
  print " "

  global lg1, lg2, dt1, dt2

  #Lightgate 1
  if channel==13:               #detect if lightgate 1 is triggered

    lg1 = 1
    dt1 = dt                    #remember date/time as dt1

    if lg2==1:                  #check if lightgate 2 was triggered already

      ddt = dt1-dt2             #calculate time difference between lightgate 1 and 2
      s = "Goodbye birdey!"     #string mentions that the bird just left the birdhouse

  #Lightgate 2
  if channel==15: #detect if lightgate 2 is triggered

    lg2 = 1
    dt2 = dt            #remember date/time as dt2

    if lg1==1:          #check if lightgate 1 was triggered already

      ddt = dt2 - dt1       #calculate time difference between lightgate 2 and 1
      s =  "Hello birdey!"  #string mentions that the bird just entered the birdhouse

  if lg1*lg2 == 1:      #if both lightgates were triggered, reset the status

    lg1 = 0
    lg2 = 0

    print s
    print " "
    print "dt2      : ", dt2
    print "dt1      : ", dt1
    print "time diff: ", ddt
    print " "

    #calculate time difference between lightgates in microseconds (us)
    deltat = 1000000*ddt.seconds+ddt.microseconds #us

    #determine decimal precision
    getcontext().prec = 2

    print "distance : ", Decimal(distance), "um"
    print "deltaT   : ", Decimal(deltat), "us"
    print " "

    #calculate speed of bird leaving/entering the birdhouse
    print "speed    : ", Decimal(distance) / Decimal(deltat), "m/s"
    print " "

#-----------------------------------------------------------#
#                     GPIO edge trigger                     #
#-----------------------------------------------------------#

#Check for falling edge of input pins. Call function LIGHTGATE if triggered
GPIO.add_event_detect(15,GPIO.FALLING,callback=lightgate,bouncetime=200)
GPIO.add_event_detect(13,GPIO.FALLING,callback=lightgate,bouncetime=200)

#-----------------------------------------------------------#
#                 main loop... sleeping...                  #
#-----------------------------------------------------------#
try:

  while True:
    sleep(1)    #Sleep as long as no edge is triggered

#-----------------------------------------------------------#
#               Watch for keyboard interupt                 #
#-----------------------------------------------------------#

except KeyboardInterrupt:  #CTRL+C
  print "KEYBOARD INTERRUPT (CTRL+C)!"

finally:
  print "Cleaning up..."
  GPIO.cleanup()
  print "Done."