#!/usr/bin/python

import pigpio
import time,sys

_TRIG=5             # hc-sr04 tigger pin
_ECHO=6             # hc-rc04 echo pin
                    # this one must be brought down to 3.3V
		    # from the hc-sr04 5V level through a level converter
pi = pigpio.pi()    # access the local Pi's gpio
if pi.connected == False:

    print "connection error"
    sys.exit(-1)
else:
    print "successfully connected"
pi.set_mode (_TRIG, pigpio.OUTPUT)
pi.set_mode (_ECHO, pigpio.INPUT)
# pi.write(_ECHO, pigpio.LOW)

print "hardware revision " + str(pi.get_hardware_revision())
count = 0

while True:
    
    print "triggering"
    pi.gpio_trigger(_TRIG,10,1)
#    pi.write(_TRIG,pigpio.HIGH)
#    time.sleep(0.000002)       # wait 10 us
#    pi.write(_TRIG,pigpio.LOW)

#    while pi.read(_ECHO) == pigpio.LOW:
#        count += 1
#        print count
    timeout = time.time()
    while pi.read(_ECHO) == 0:
        start = time.time()
        if start - timeout > 5:
            print "timeout: signal not coming high"
            continue

    while pi.read(_ECHO) == 1:
        stop = time.time()
        if stop - start > 5:
            print "timeout: signal not going low"
            continue

#    print count
    duration = stop - start
    distance = duration * 17150
    
    print "distance: " + str(distance) + "cm"
    time.sleep(1)