proximityClass.py

import RPi.GPIO as GPIO
import json
import time
from componentClass import Component


class ProximitySensor(Component):
    """
    An implementation of the component used to request data from the
    motor periodically, which then sends it to the corresponding topic
    to be read by the API
    """

    # Setup method for this specific device
    def setup(self,samplingInterval):
        self.sampInterval = samplingInterval
        self.set_topic("proximity")

        # Setup the GPIO pins
        self.TRIG = 17
        self.ECHO = 27
        GPIO.setmode(GPIO.BCM)
        GPIO.setup(self.TRIG, GPIO.OUT)
        GPIO.setup(self.ECHO, GPIO.IN)
        GPIO.output(self.TRIG, False)
        GPIO.setwarnings(False)
        time.sleep(1)
        self.filtered_distance = [0.0] * 3
        print "{} setup finished".format(self.name)

    # Data Handling for this specific device, from collection to publishing to
    # the correct MQTT Topics.
    def handleData(self, timestamp):
        self.mqttHandler.publish(self.my_topic, json.dumps(
            self.gen_payload_message(self.measureDistance(), timestamp)),
            retain=True)

    # Generates the payload specific to the IMU
    def gen_payload_message(self, distance, timestamp):
        return {
            'distance': distance,
            'timestamp': timestamp
        }

    def measureDistance(self):
        # Trigger the sensor
        GPIO.output(self.TRIG, True)
        time.sleep(0.00001)
        GPIO.output(self.TRIG, False)
        pulse_start = 0
        pulse_end = 0

        # Wait for Sonar Response
        begin = time.time()
        while GPIO.input(self.ECHO) == 0:
            pulse_start = time.time()
            if (pulse_start - begin) > 0.01:
                begin = 1
                break
        if begin == 1:
            return round((sum(self.filtered_distance) / 3), 2)

        else:
            while GPIO.input(self.ECHO) == 1:
                pulse_end = time.time()

        # Get the duration of the pulsem which indicates the time
        # it took for the sound wave to come back
        pulse_duration = pulse_end - pulse_start
        distance = pulse_duration * 17150.0
        if distance < 4:
            distance = 4
        # Calculate the distance in cm based on the speed of sound/2
        del self.filtered_distance[0]
        self.filtered_distance.append(distance)
        # Round to 2 decimal points
        return round((sum(self.filtered_distance) / 3), 2)