NodeMCU (ESP8266) / HC-SR04 with MQTT support

Introduction

Hello! This application was written with the purpose of measuring the coal level in my furnace storage and publish it over MQTT to my OpenHab installation. The hardware used in the excellent ESP8266 with a distance sensor HC-SR04.

Features

Even though the code is small it has several useful features:

• HC-SR04 measurement, both single and continuous (timer based)

• Wifi connection

• MQTT connection with auto-reconnect

• Subscribes to own channel for command inception

Setup

Besides uploading all *.lua code files you need to create manually one more file, namely credentials.lua. It should contain the connection details to both your WiFi and MQTT broker.

credentials.lua contents:

SSID

The SSID of your WiFi network

PASSWORD

WiFi password

MQTT_HOST

Host address of the MQTT broker

MQTT_PORT

Port of the MQTT broker

MQTT_USER

Username to access the broker

MQTT_PASSWORD

Password for MQTT user

HC-SR04 connection

In my setup the HC-SR04 is connected to pins D3 and D4 on the board (echo and trigger respectively) → see application.lua PIN_TRIG and PIN_ECHO.

Ground and VCC are connected to GND and VTA. Be aware that sometimes if you have too weak power source the board might not boot up with sensor connected.

This happened for me when debugging, I had to first disconnect sensor, reset board, then upload files, restart again and connect sensor live. But when used with phone charger (5V - 2A) everything worked flawlessly.

MQTT

Connection to MQTT broker (I use Mosquitto) is initialized manually but after that it is automatically reconnected. Also the connection is first established upon first published message.

By default the channel is named coal and the client id is coalo. The MQTT client also establishes a subscription to a command channel named after client id (coalo here) — but only if a callback function is given.

Usage

Simply upload all the *.lua files to the board and restart. Upon successful WiFi connection the MQTT broker connection should be initialized and first measurement started.

Result is always made as an average of 3 consecutive measurements. Even with this results can be sometimes way off - I think this is due to sensor limitations.

When you give a callback function to MqttClient (see application.lua) it then subscribes to a command channel named after client id (coalo by default).

If you publish something to that channel it will be picked up and processed. Currently the only recognized command is update. It forces an immediate measurement. So even if you have set up a continuous work but the delay is high, you can enforce an update.

For example:

mosquitto_pub -h mqtt_host -p mqtt_port -u mqtt_user -P mqtt_password -t coalo -m "update"

Hope you find this useful. Thanks!