import time
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)

GPIO.setup(26, GPIO.IN, pull_up_down = GPIO.PUD_DOWN)

i = 0

start = time.time()

while time.time() - start < 60:
        GPIO.wait_for_edge(26, GPIO.FALLING)
        i += 1

watts = i*3600.0/10.0

print watts, "Watts"

GPIO.cleanup()