#
# hello.HC-SR04.py
#
# HC-SR04 sonar hello-world
#    hello.HC-SR04.py serial_port
#
# Neil Gershenfeld 11/15/15
# (c) Massachusetts Institute of Technology 2015
#
# This work may be reproduced, modified, distributed,
# performed, and displayed for any purpose. Copyright is
# retained and must be preserved. The work is provided
# as is; no warranty is provided, and users accept all
# liability.
#

# from Tkinter import *
import serial
import sys

prev_value = 0

def main():
    global prev_value

    # idle routine
    byte2 = 0
    byte3 = 0
    byte4 = 0
    ser.flush()
    while 1:
        # find framing
        byte1 = byte2
        byte2 = byte3
        byte3 = byte4
        byte4 = ord(ser.read())
        if ((byte1 == 1) & (byte2 == 2) & (byte3 == 3) & (byte4 == 4)):
            break
    low = ord(ser.read())
    high = ord(ser.read())
    value = (256 * high + low)
    if abs(value - prev_value) > 10:
        print(value)
    prev_value = value

#  check command line arguments
if (len(sys.argv) != 2):
    print "command line: hello.HC-SR04.py serial_port"
    sys.exit()
port = sys.argv[1]

# open serial port
ser = serial.Serial(port, 9600)
ser.setDTR()

while 1:
    main()