import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BOARD)
GPIO.setup(18,GPIO.OUT)
GPIO.setup(16,GPIO.IN)
fanpwm = GPIO.PWM(18,25000)

def getRPM():
    start=int(time.time())
    c=0
    state=False

    while (int(time.time()) <= start + 10):
        if GPIO.input(16):
            if (state == False):
                c=c+1
                state=True
            else:
                state=False

    rpm=(c*6)/2
    return rpm

fanpwm.start(0)
time.sleep(2)
fanpwm.start(100)
time.sleep(2)
fanpwm.start(0)
time.sleep(2)
fanpwm.start(100)
time.sleep(2)

for x in range(100,-1,-1):
    fanpwm.ChangeDutyCycle(x)
    print str(getRPM())
    time.sleep(0.25)