BigClown - mqtt microservice - convert voltage to percentage

bc-battery_pct.py

import paho.mqtt.client as mqtt

# Configuration
################

## Server
mqtt_server = "turris"
mqtt_port = 1883

# Core module minimal voltage
module_critical_voltage = 2.0

# List of nodes
nodes = { "836d1982196f": { "cells": 2,
                            "cell_voltage": 1.6
                          },
          "836d19820e43": { "cells": 4,
                            "cell_voltage": 1.6
                          },
            "AAA":        { "cells": 2,
                            "cell_voltage": 1.6
                          }
        }

# Functions
###########

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("node/+/battery/+/voltage")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print("Topic: "+msg.topic+", payload: "+str(msg.payload))

    if str(msg.payload) == "b''":
        print("Null message!")
        return

    node_id = msg.topic.split("/")[1]
    node_type = msg.topic.split("/")[3]

    if nodes.get(node_id) == None:
        print("Unknown node: {0}".format(node_id))
        return

    topic_pct = "node/{0}/battery/{1}/percentage".format(node_id, node_type)
    topic_level= "node/{0}/battery/{1}/level".format(node_id, node_type)

    percentage = int(100 * (float(msg.payload) - module_critical_voltage) / (nodes[node_id]["cells"] * nodes[node_id]["cell_voltage"] - module_critical_voltage))


    if percentage > 100 :
        percentage = 100
    elif percentage < 0 :
        percentage = 0

    client.publish(topic_pct, percentage);

    if percentage > 80 :
        level = "high"
    elif percentage > 20 :
        level = "middle"
    elif percentage > 5 :
        level = "low"
    else :
        level = "critical"

    client.publish(topic_level, level);


########
# Main #
########

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect(mqtt_server, mqtt_port, 60)

# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
client.loop_forever()