ESP8266 and MicroPython - Part 2

Fabian Affolter August 31, 2016

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So, part 1 of [ESP8266 and MicroPython](/blog/2016/07/28/esp8266-and-micropython-part1/) 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 the information for the sensor? 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 in Home Assistant or it could be missed. This means the sensor must take initiative and send the data to Home Assistant.

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.