ESP8266 and MicroPython - Part 2

three minutes reading time
  • ESP8266
  • How-To
  • MQTT
  • Micropython
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So, part 1 of ESP8266 and MicroPython was pretty lame, right? Instead of getting information out of Home Assistant we are going a step forward and create our own sensor which is sending details about its state to a Home Assistant instance.

Beside HTTP POST requests, MQTT is the quickest way (from the author’s point of view) to publish information with DIY devices.

You have to make a decision: Do you want to pull or to poll? For slowly changing values like temperature it’s perfectly fine to wait a couple of seconds to retrieve the value. If it’s a motion detector the state change should be available instantly. This means the sensor must take initiative.

An example for pulling is aREST. This is a great way to work with the ESP8266 based units and the Ardunio IDE.

MQTT

You can find a simple examples for publishing and subscribing with MQTT in the MicroPython library overview in the section for umqtt.

The example below is adopted from the work of @davea as we don’t want to re-invent the wheel. The configuration feature is crafty and simplyfies the code with the usage of a file called /config.json which stores the configuration details. The ESP8266 device will send the value of a pin every 5 seconds.

import machine
import time
import ubinascii
import webrepl

from umqtt.simple import MQTTClient

# These defaults are overwritten with the contents of /config.json by load_config()
CONFIG = {
    "broker": "192.168.1.19",
    "sensor_pin": 0, 
    "client_id": b"esp8266_" + ubinascii.hexlify(machine.unique_id()),
    "topic": b"home",
}

client = None
sensor_pin = None

def setup_pins():
    global sensor_pin
    sensor_pin = machine.ADC(CONFIG['sensor_pin'])

def load_config():
    import ujson as json
    try:
        with open("/config.json") as f:
            config = json.loads(f.read())
    except (OSError, ValueError):
        print("Couldn't load /config.json")
        save_config()
    else:
        CONFIG.update(config)
        print("Loaded config from /config.json")

def save_config():
    import ujson as json
    try:
        with open("/config.json", "w") as f:
            f.write(json.dumps(CONFIG))
    except OSError:
        print("Couldn't save /config.json")

def main():
    client = MQTTClient(CONFIG['client_id'], CONFIG['broker'])
    client.connect()
    print("Connected to {}".format(CONFIG['broker']))
    while True:
        data = sensor_pin.read()
        client.publish('{}/{}'.format(CONFIG['topic'],
                                          CONFIG['client_id']),
                                          bytes(str(data), 'utf-8'))
        print('Sensor state: {}'.format(data))
        time.sleep(5)

if __name__ == '__main__':
    load_config()
    setup_pins()
    main()

Subscribe to the topic home/# or create a MQTT sensor to check if the sensor values are published.

$ mosquitto_sub -h 192.168.1.19 -v -t "home/#"
sensor:
  - platform: mqtt
    state_topic: "home/esp8266_[last part of the MAC address]"
    name: "MicroPython"

@davea created sonoff-mqtt. This code will work on ESP8622 based devices too and shows how to use a button to control a relay.

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