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MicroPython library to create sensors for HomeAssistant using MQTT Discovery

This is a simple MicroPython library which allows to create sensors and group of sensors for HomeAssistant. The library makes use of the HomeAssistant MQTT Discovery method by announcing the devices through a configuration topic.

Getting Started

Prerequisites

MicroPython board capable of sending MQTT messages
HomeAssistant with MQTT Broker running
Some kind of sensor (not mandatory, but useful ;-))

Usage

MQTT Client

First a MQTT Client needs to be created. The module umqtt.simple provides a simple MQTT client. The module can be installed using upip. Make sure you are connected to the internet, e.g. using WiFi:

import network
wl = network.WLAN(network.STA_IF)
wl.active(True)
wl.connect(<SSID>, <PSK>)
wl.config(dhcp_hostname="Testboard")

Install the umqtt.simple module and create a MQTTClient object:

upip.install("micropython-umqtt.simple")
from umqtt.simple import MQTTClient
mqttc = MQTTClient(b"umqtt-testboard", <MQTT Server IP>, keepalive=10)
mqttc.connect()

Basic sensor

This example creates a single sensor and announces values. The second argument to the Sensor constructor is the name argument and will be the entity name in HomeAssistant. The argument extra_config allows to pass additional configuration values as specified by the MQTT Sensor Component. In this case the device class and unit of measurement of the sensor is specified.

With the creation of the Sensor object a persistent MQTT message is sent to the discovery topic. The configuration will be picked up by HomeAssistant and a sensor is created. The topic for the entites states update is handled by the class.

The publish_state() function will send the MQTT message to the state topic which will update the state of the particular entity in HomeAssistant.

# Temperature sensor...
import time
temp_config = { "unit_of_measurement": "°C", "device_class": "temperature" }
temp = Sensor(mqttc, b"temperature_sensor", b"sensorid", extra_conf=temp_config)
for i in range(10, 30):
    temp.publish_state(str(i))
    time.sleep(1)

# This deletes the sensor from HomeAssistant as well!
temp.remove_entity()

Multiple sensors

Multiple entities can share the same MQTT state topic. This allows to send a single (JSON formatted) MQTT message to update multiple entites in HomeAssistant. For this each entity needs to have a value_template specified so each entity know which value it needs to parse.

group = EntityGroup(mqttc, b"testboard")
sensor1_config = { "unit_of_measurement": "°C", "device_class": "temperature",
    "value_template": "{{ value_json.temperature }}" }
sensor1 = group.create_sensor(b"test1", b"test1id", extra_conf=sensor1_config)

sensor2_config = { "unit_of_measurement": "%", "device_class": "humidity",
    "value_template": "{{ value_json.humidity }}" }
sensor2 = group.create_sensor(b"test2", b"test2id", extra_conf=sensor2_config)

To update the group the publish_state() function on the group object needs to be used:

for i in range(10, 30):
    group.publish_state({ "temperature": str(i), "humidity": str(10 + i) })
    time.sleep(1)

To delete all entities of this group:

group.remove_group()

Multiple sensors with Device registry

HomeAssistant allows to group entites into devices via the Device Registry concept. MQTT entities allow to use the device registry to group individual entities to a device as well.

For this to work a device dictionary needs to be added to the configuration variable. A unique_id property with a unique ID for each entity is required too.

device_conf = { "identifiers": [ "common_identifier" ], "name": "Testboard",
    "manufacturer": "MicroPython", "model": "TinyPico", "sw_version": "0.1" }
common_conf = { "device": device_conf }
group = EntityGroup(mqttc, b"testboarder", extra_conf=common_conf)

sensor1_config = { "unit_of_measurement": "°C", "device_class":
    "temperature", "value_template": "{{ value_json.temperature }}"),
    "unique_id": mqtt_status + "sensor1"}
sensor1 = group.create_sensor(b"test1", b"test1id", extra_conf=sensor1_config)

sensor2_config = { "unit_of_measurement": "%", "device_class":
    "humidity", "value_template": "{{ value_json.humidity }}",
    "unique_id": mqtt_status + "sensor2"}
sensor2 = group.create_sensor(b"test2", b"test2id", extra_conf=sensor2_config)

Publishing state and removing the group stays the same as regular entity groups.

Using availability topic

MQTT allows to specify a last will message which is sent to the specified topic when a device does not connect for a certain period. The last will message is transmitted when connecting, hence this needs to be configured before connecting. Also choose a keep alive timeout which is higher than your expected sensor update time. E.g. if you plan to update the sensor value every minute, a value higher than 60 seconds make sense. The same topic then needs to be specified when creating the sensor:

mqtt_availability_topic = b"testboard/status"
mqttc = MQTTClient(b"umqtt-testboard", <MQTT Server IP>, keepalive=70)
mqttc.set_last_will(mqtt_status, b"offline", True)
mqttc.connect()
mqttc.publish(mqtt_status, b"online", retain=True)

temp_config = { "availability_topic": mqtt_availability_topic }
temp = Sensor(mqttc, b"temperature_sensor", b"sensorid", extra_conf=temp_config)

License

This project is licensed under the MIT License - see the LICENSE file for details