Sample solution

sample/publish_sample.py

+import datetime
+import json
+import random
+import numpy as np
+import time
+import uuid
+import os
+
+from wzl import mqtt
+
+### Time series creator
+
+T0 = 75 # Inital tem perature in degrees
+tau = 180 # decay factor in s 
+
+def exponential_decay(t, A0, tau, noise_factor=0.5):
+    value = (A0-21) * np.exp(-t / tau) + 21 
+    value += np.random.normal(0, noise_factor * np.sqrt(value))
+    return value
+
+### Function to embed sensor value into MQTT2Influx bridge format
+
+def soil_msg(value, unit="MTR", nonce = dict(uuid=str(uuid.uuid4()))):
+    """
+    value := sensor value, list
+    unit  := unit of the value, str
+    nonce := arbitrary dictionary of metadata, dict 
+    """
+    return json.dumps({"value": [value], "timestamp": datetime.datetime.utcnow().isoformat() + "Z",
+                                "nonce": nonce, "hash": None, "unit": unit})
+
+### Ask for settings and individual credentials ###
+
+## TODO 2: Use your credentials and the correct config for connecting to the MQTT broker at WZL
+MQTT_USER = os.environ["MQTT_USER"] # to be changed to your individual credentials or save your credentials in an environment variable called MQTT_USER, too
+MQTT_PASSWORD =  os.environ["MQTT_PASSWORD"] # to be changed to your individual credentials or save your credentials in an environment variable called MQTT_PASSWORD, too
+
+# MQTT_BROKER = "127.0.0.1"
+MQTT_PORT = 1883
+
+## TODO 1: Change the topic and observe what happens in the receiver output
+## TODO 2: Change the topic to soil-conform format
+MQTT_TOPIC = "OBJ-Env/VAR-Temperature"
+
+## TODO 3: Add a soil-conform status topic 
+MQTT_TOPIC_Status ="OBJ-Env/VAR-Status"
+
+### to connect to the central MQTT-Broker of MQ-MS use the following settings:
+MQTT_BROKER = "134.130.175.204"
+MQTT_VHOST = "metrology"
+
+### Ask for settings and individual credentials ###
+
+# time steps
+t = 0 # s
+
+if __name__ == "__main__":
+    # The publisher and receiver classes may consider a prefix, that is put in front of each topic
+    ## TODO 2: Add the WS b24 prefix to the Publisher 
+    client = mqtt.MQTTPublisher(prefix="b24")
+    client.connect(MQTT_BROKER, MQTT_PORT, MQTT_VHOST + ":" + MQTT_USER, MQTT_PASSWORD)
+
+    while True:
+        try:
+            # Message field
+            ## TODO Task 1: Change the message string and observe what happens with the transmitted message 
+            ## TODO Task 2: a) Use the soil_msg function defined above to bring your message into the soil-conform format.
+            ##              b) Use the exponential decay function from above and and pass a meaningful unit and a dictionary that includes a keyword "name" and as value your name 
+            message = soil_msg(exponential_decay(t, T0, tau), "K", nonce=dict(name="Dominik"))
+            client.publish(MQTT_TOPIC, message.encode("utf-8"), 0)
+           
+            time.sleep(1)
+            ## TODO Task 3: Create a second soil message that transmits the status of your demonstrator (0 = running, 1 = Off, 2=Maintenance) to the broker and publish it under a dedicated topic
+            message = soil_msg(1, "", nonce=dict(name="Dominik"))
+            client.publish(MQTT_TOPIC_Status, message.encode("utf-8"), 0)
+
+            # increase time step variable
+            t += 1
+        except KeyboardInterrupt:
+            break