import RPi.GPIO as GPIO
from time import sleep

class Fan:
    def __init__(self):
        GPIO.setmode(GPIO.BCM)
        
        #prepare switch GPIO port
        self.switchPin = 22
        GPIO.setup(self.switchPin, GPIO.OUT)
        
        #prepare PWM GPIO port
        pwmPin = 27
        GPIO.setup(pwmPin, GPIO.OUT)
        self.pwm = GPIO.PWM(pwmPin, 2000) #Notice: The target frequency for PWM on PC Ventilators is 25kHz. However, the Raspberry Pi 2, I am using for testing, appears not to be able to switch the Pin with that high frequency in a clean manner. But the Fan appears to accept the 2kHz. That might not apply to each and every fan out there.
        
        #prepare TACH GPIO port
        self.tachPin = 17
        GPIO.setup(self.tachPin, GPIO.IN)

    def start(self):
        GPIO.output(self.switchPin, 1)
        self.setFullSpeed()
    
    def stop(self):
        GPIO.output(self.switchPin, 0)
        self.pwm.stop()
    
    def setSpeed(self, percent):
	    #some sanity esurance
        percent = 100 if percent > 100 else percent
        percent = 0 if percent < 0 else percent
                
        #compensation for inverted PWM signal
        dc = 100 - percent
        
        self.pwm.stop()
        self.pwm.start(dc)
        
    def setFullSpeed(self):
        self.setSpeed(100)
    
    def setSlowSpeed(self):
        self.setSpeed(0)
    
    def getSpeed(self):
        self.rpmCount = 0
        GPIO.add_event_detect(self.tachPin, GPIO.RISING, callback=self.rpmCounter)
        sleep(2)
        GPIO.remove_event_detect(self.tachPin)
        pwm = (self.rpmCount/2) * 30 #Notice: The Fan I am using generates two risings per revolution. While many PC-Fans work that way, that again might not apply to every fan. We measure for 2 seconds, means 30 times per minute.
        return pwm
    
    def rpmCounter(self, pin):
        self.rpmCount += 1

#TESTING PROGRAM
print("start Fan")
fan = Fan()
fan.start()
sleep(15)

print "RPM is {0}".format(fan.getSpeed())
print("set fan to 75")
fan.setSpeed(75)
sleep(15)

print "RPM is {0}".format(fan.getSpeed())
print("set fan to 50")
fan.setSpeed(50)
sleep(15)

print "RPM is {0}".format(fan.getSpeed())
print("set fan to 25")
fan.setSpeed(25)
sleep(15)

print "RPM is {0}".format(fan.getSpeed())
print("set fan to slow")
fan.setSlowSpeed()
sleep(15)

print "RPM is {0}".format(fan.getSpeed())
print("set fan to full speed")
fan.setFullSpeed()
sleep(15)

print "RPM is {0}".format(fan.getSpeed())
print("stop Fan")
fan.stop()

GPIO.cleanup()