ultraspi.py

# On 7/13/15 John Bohlhuis contribute his own Python code that he is using to automate the reading of distance values. 
# We gladly share this for your use in your projects. 
# Thank you John for sharing. 


# ***************************************************************************
# First, the Python module that does the actual work:
# ***************************************************************************

#!/usr/bin/python3
# Filename: maxSonarTTY.py

# Reads serial data from Maxbotix ultrasonic rangefinders
# Gracefully handles most common serial data glitches
# Use as an importable module with "import MaxSonarTTY"
# Returns an integer value representing distance to target in millimeters

from time import time
from serial import Serial

serialDevice = "/dev/ttyAMA0" # default for RaspberryPi
maxwait = 3 # seconds to try for a good reading before quitting

def measure(portName):
    ser = Serial(portName, 9600, 8, 'N', 1, timeout=1)
    timeStart = time()
    valueCount = 0

    while time() < timeStart + maxwait:
        if ser.inWaiting():
            bytesToRead = ser.inWaiting()
            valueCount += 1
            if valueCount < 2: # 1st reading may be partial number; throw it out
                continue
            testData = ser.read(bytesToRead)
            if not testData.startswith(b'R'):
                # data received did not start with R
                continue
            try:
                sensorData = testData.decode('utf-8').lstrip('R')
            except UnicodeDecodeError:
                # data received could not be decoded properly
                continue
            try:
                mm = int(sensorData)
            except ValueError:
                # value is not a number
                continue
            ser.close()
            return(mm)

    ser.close()
    raise RuntimeError("Expected serial data not received")

if __name__ == '__main__':
    measurement = measure(serialDevice)
    print("distance =",measurement)


# ***************************************************************************
# Also, here is a sample Python script that shows how the module may be used:
# ***************************************************************************

#!/usr/bin/python3
# Filename: rangeFind.py

# sample script to read range values from Maxbotix ultrasonic rangefinder

from time import sleep
import maxSonarTTY

serialPort = "/dev/ttyAMA0"
maxRange = 5000  # change for 5m vs 10m sensor
sleepTime = 5
minMM = 9999
maxMM = 0

while True:
    mm = maxSonarTTY.measure(serialPort)
    if mm >= maxRange:
        print("no target")
        sleep(sleepTime)
        continue
    if mm < minMM:
        minMM = mm
    if mm > maxMM:
        maxMM = mm

    print("distance:", mm, "  min:", minMM, "max:", maxMM)
    sleep(sleepTime)