layout: post

title: "ESP8266 and MicroPython - Part 2"

description: "Export, process, and visualize data stored by Home Assistant."

date: 2016-08-31 06:17:25 +0200

date_formatted: "August 31, 2016"

author: Fabian Affolter

comments: true

categories: How-To MQTT ESP8266 Micropython

og_image: /images/blog/2016-07-micropython/social.png

<img src='/images/blog/2016-07-micropython/micropython.png' style='clear: right; border:none; box-shadow: none; float: right; margin-bottom: 12px;' width='200' />

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](https://en.wikipedia.org/wiki/POST_(HTTP)) 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](/components/sensor.arest/). This is a great way to work with the ESP8266 based units and the Ardunio IDE.

You can find a simple examples for publishing and subscribing with MQTT in the [MicroPython](https://github.com/micropython/micropython-lib) library overview in the section for [umqtt](https://github.com/micropython/micropython-lib/tree/master/umqtt.simple).

The example below is adopted from the work of [@davea](https://github.com/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

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](/components/sensor.mqtt/) 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"