import time

'''
hcsr04_funcs: Helper functions to interact with the HC-SR04 sensor.
'''

def read_hc_sr04(trig, echo):
    """
        reads the HC-SR04 sensor.
        returns tuple(temperature, humidity) if no errors
        returns None if there was an error
    """
    try:
        trig.value(0)
        time.sleep(0.1)
         
        trig.value(1)
        time.sleep_us(2)
        
        trig.value(0)
        
        while echo.value()==0:
             pulse_start = time.ticks_us()
        
        while echo.value()==1:
             pulse_end = time.ticks_us()
        
        pulse_duration = pulse_end - pulse_start
        distance = pulse_duration * 17165 / 1000000
        distance = round(distance, 2)
        
        return distance
    except:
        return None