MQTT Communication Extension for Sensor Implementation

We extend our last approach in Listing 1 with the MQTT communication protocol in Listing 2, so that we can transmit the sensor measurement data. You can find this version of the code in the repository with the filename distance_sensor_simple_with_MQTT.py.

 
import RPi.GPIO as GPIO
import time
import paho.mqtt.client as mqtt

HOST = "test.mosquitto.org"
PORT = 1883

client = mqtt.Client()
client.connect(HOST, PORT)


# use Raspberry Pi board pin numbers
GPIO.setmode(GPIO.BOARD)

# set GPIO Pins
PIN_TRIGGER = 7
PIN_ECHO = 11

print("Distance Measurment In Progress")

# set GPIO input and output channels
GPIO.setup(PIN_TRIGGER, GPIO.OUT)
GPIO.setup(PIN_ECHO, GPIO.IN)

while True:
        # set Trigger to HIGH
        GPIO.output(PIN_TRIGGER, True)
        # set Trigger after 0.01ms to LOW
        time.sleep(0.00001)
        GPIO.output(PIN_TRIGGER, False)

        startTime = time.time()
        stopTime = time.time()

        # save start time
        while GPIO.input(PIN_ECHO) == 0:
                pass
        startTime = time.time()

        # save time of arrival
        while GPIO.input(PIN_ECHO) == 1:
                pass
        stopTime = time.time()

        # time difference between start and arrival
        TimeElapsed = stopTime - startTime
        # multiply with the sonic speed (34300 cm/s)
        # and divide by 2, because there and back
        distance = (TimeElapsed * 34300) / 2

        print ("Distance: %.1f cm" % distance)

        client.publish("/test/distance", "Distance={0:0.1f} cm".format(distance))
        client.subscribe("/test/distance")

        time.sleep(1)

Listing 2: Simple approach with MQTT communication protocol

To run the code in Listing 2, you first need to install a Mosquitto MQTT Broker:

sudo apt-get install mosquitto

Now you can run the above code in Listing 2 simply by calling the following command:

python distance_sensor_simple_with_MQTT.py