Publishing MQTT messages from a NodeMCU – Soil Moisture Sensor

May 8, 2016May 8, 2016 iotalotc 0 Comments ESP8266, nodemcu

In this article I’d like to share the experience of building a soil moisture sensor built on NodeMCU which publishes MQTT messages (payload) to a cloud service.

This article is also a soft launch of a preview of cloud.iotalot.com service. We use it for our DIY projects to register json payload and visualise it is a very simple way. This allows us to “debug” our sensors. If you wish to get access to cloud.iotalot.com let us know by sending an email to admin@iotalot.com. We will provide you with the user account and instruct on how to start your project.
DISCLAIMER: We are not responsible for any data privacy or availability of the service at the moment.

Now back to the “experience” …

The set up

The sensor is mounted on the flower pot

Every 10 minutes is sends MQTT payload to cloud.iotalot.com

I can check the sensor data records using the telegram bot

This is how the components look like

The code

I assume you have a nodeMCU with the firmware burnt like explained in the post earlier. The firmware version that is used in this example is the following: nodemcu_float_0.9.6-dev_20150704.bin

This is the code for init.lua and moisturesensor.lua .
As a best practice, I don’t put the main code to int.lua file so that I can play with the NodeMCU module when the main code has some loops or timers. Before going to “production” I just put dofile("moisture sensor.lua") to init.lua to make sure the main code runs when the device is powered.

init.lua

dofile("moisturesensor.lua")

1	dofile("moisturesensor.lua")

moisturesensor.lua

local WIFI_SSID = "{WIFI_SSID}"
local WIFI_PASS = "{WIFI_PASS}"

local MAINTIMER_ID = 0
-- every 10 minutes = 600000ms
local MAINTIMER_INTERVAL_MS = {INTERVAL}

local mqtt_client = {}
local MQTT_CLIENTID = "{MQTT CLINT_ID STRING}"
local MQTT_USER = "{cloud.iotalot.com USERNAME}"
local MQTT_PASS = "{cloud.iotalot.com PASSWORD}"
local MQTT_TOPIC = "iotalot/sensors/{SENSOR_APIKEY}"
local MQTT_ADDR = "cloud.iotalot.com"
local MQTT_PORT = {MQTT_PORT}

print("Moisture Sensor Initialized")

function send_moisture_mqtt()
    moisture = adc.read(0)
    r = mqtt_client:publish(MQTT_TOPIC, string.format("{\"moisture\": %d}", moisture), 1, 1)
end

function register_main_timer()
    -- sending once the moisture wnen devices initialized
    send_moisture_mqtt()
    -- registering a timer
    tmr.register(MAINTIMER_ID, MAINTIMER_INTERVAL_MS, tmr.ALARM_AUTO, send_moisture_mqtt)
    tmr.start(MAINTIMER_ID)
end

function init_mqtt_client()
    -- init mqtt client with keepalive timer 120sec
    mqtt_client = mqtt.Client(MQTT_CLIENTID, 120, MQTT_USER, MQTT_PASS)    
    mqtt_client:connect(MQTT_ADDR, MQTT_PORT, register_main_timer, function(client, reason) print("failed reason: "..reason) end)
end

function wait_for_wifi_conn ( )
   tmr.alarm (1, 1000, 1, function ( )
      if wifi.sta.getip ( ) == nil then
         print ("Waiting for Wifi connection")
      else
         tmr.stop (1)
         print ("The mode is: " .. wifi.getmode ( ))
         print ("The module MAC address is: " .. wifi.ap.getmac ( ))
         print ("Config done, IP is " .. wifi.sta.getip ( ))
         -- creating the mqqt client
         init_mqtt_client()
      end
   end)
end

-- Configure the ESP as a station (client)
wifi.setmode (wifi.STATION)
wifi.sta.config (WIFI_SSID, WIFI_PASS)
wifi.sta.autoconnect (1)

-- Hang out until we get a wifi connection before the httpd server is started.
wait_for_wifi_conn ( )

local WIFI_SSID = "{WIFI_SSID}"

local WIFI_PASS = "{WIFI_PASS}"

local MAINTIMER_ID = 0

-- every 10 minutes = 600000ms

local MAINTIMER_INTERVAL_MS = {INTERVAL}

local mqtt_client = {}

local MQTT_CLIENTID = "{MQTT CLINT_ID STRING}"

local MQTT_USER = "{cloud.iotalot.com USERNAME}"

local MQTT_PASS = "{cloud.iotalot.com PASSWORD}"

local MQTT_TOPIC = "iotalot/sensors/{SENSOR_APIKEY}"

local MQTT_ADDR = "cloud.iotalot.com"

local MQTT_PORT = {MQTT_PORT}

print("Moisture Sensor Initialized")

function send_moisture_mqtt()

moisture = adc.read(0)

r = mqtt_client:publish(MQTT_TOPIC, string.format("{\"moisture\": %d}", moisture), 1, 1)

end

function register_main_timer()

-- sending once the moisture wnen devices initialized

send_moisture_mqtt()

-- registering a timer

tmr.register(MAINTIMER_ID, MAINTIMER_INTERVAL_MS, tmr.ALARM_AUTO, send_moisture_mqtt)

tmr.start(MAINTIMER_ID)

end

function init_mqtt_client()

-- init mqtt client with keepalive timer 120sec

mqtt_client = mqtt.Client(MQTT_CLIENTID, 120, MQTT_USER, MQTT_PASS)

mqtt_client:connect(MQTT_ADDR, MQTT_PORT, register_main_timer, function(client, reason) print("failed reason: "..reason) end)

end

function wait_for_wifi_conn ( )

tmr.alarm (1, 1000, 1, function ( )

if wifi.sta.getip ( ) == nil then

print ("Waiting for Wifi connection")

else

tmr.stop (1)

print ("The mode is: " .. wifi.getmode ( ))

print ("The module MAC address is: " .. wifi.ap.getmac ( ))

print ("Config done, IP is " .. wifi.sta.getip ( ))

-- creating the mqqt client

init_mqtt_client()

end

end)

end

-- Configure the ESP as a station (client)

wifi.setmode (wifi.STATION)

wifi.sta.config (WIFI_SSID, WIFI_PASS)

wifi.sta.autoconnect (1)

-- Hang out until we get a wifi connection before the httpd server is started.

wait_for_wifi_conn ( )

To configure the code for your project you need to specify the following:

{WIFI_SSID}, {WIFI_PASS} – the name of your WiFi access point and a password to it;
{INTERVAL} – the interval in milliseconds for the timer. The code will send MQTT messages every {INTERVAL} milliseconds;
{MQTT_CLIENTID} – any unique string to identify the MQTT client;
{cloud.iotalot.com USERNAME}, {cloud.iotalot.com PASSWORD} – the MQTT server username and a password;
{SENSOR_APIKEY} – the sensor apikey on cloud.iotalot.com. Feel free to modify the topic to any other when not using cloud.iotalot.com;
{MQTT_PORT} – a port of MQTT service.

The code above explained …

Configuring the NodeMCU as a WiFi station trying to connect to WIFI_SSID access point using WIFI_PASS password.

-- Configure the ESP as a station (client)
wifi.setmode (wifi.STATION)
wifi.sta.config (WIFI_SSID, WIFI_PASS)
wifi.sta.autoconnect (1)

-- Hang out until we get a wifi connection before the httpd server is started.
wait_for_wifi_conn ( )

-- Configure the ESP as a station (client)

wifi.setmode (wifi.STATION)

wifi.sta.config (WIFI_SSID, WIFI_PASS)

wifi.sta.autoconnect (1)

-- Hang out until we get a wifi connection before the httpd server is started.

wait_for_wifi_conn ( )

Every 1 second we check that the IP is provided by access point DHCP. When given we create the MQTT client and connect to MQTT server.

function wait_for_wifi_conn ( )
   tmr.alarm (1, 1000, 1, function ( )
      if wifi.sta.getip ( ) == nil then
         print ("Waiting for Wifi connection")
      else
         tmr.stop (1)
         print ("The mode is: " .. wifi.getmode ( ))
         print ("The module MAC address is: " .. wifi.ap.getmac ( ))
         print ("Config done, IP is " .. wifi.sta.getip ( ))
         -- creating the mqqt client
         init_mqtt_client()
      end
   end)
end

function wait_for_wifi_conn ( )

tmr.alarm (1, 1000, 1, function ( )

if wifi.sta.getip ( ) == nil then

print ("Waiting for Wifi connection")

else

tmr.stop (1)

print ("The mode is: " .. wifi.getmode ( ))

print ("The module MAC address is: " .. wifi.ap.getmac ( ))

print ("Config done, IP is " .. wifi.sta.getip ( ))

-- creating the mqqt client

init_mqtt_client()

end

end)

end

In the following code the call back function register_main_timer() is provided for the case when connected successfully to MQTT server:

function init_mqtt_client()
    -- init mqtt client with keepalive timer 120sec
    mqtt_client = mqtt.Client(MQTT_CLIENTID, 120, MQTT_USER, MQTT_PASS)    
    mqtt_client:connect(MQTT_ADDR, MQTT_PORT, register_main_timer, function(client, reason) print("failed reason: "..reason) end)
end

function init_mqtt_client()

-- init mqtt client with keepalive timer 120sec

mqtt_client = mqtt.Client(MQTT_CLIENTID, 120, MQTT_USER, MQTT_PASS)

mqtt_client:connect(MQTT_ADDR, MQTT_PORT, register_main_timer, function(client, reason) print("failed reason: "..reason) end)

end

In the following part tmr.ALARM_AUTO means that timer doesn’t stop when once triggered. send_moisture_mqtt is called when timer is triggered.

function register_main_timer()
    -- sending once the moisture wnen devices initialized
    send_moisture_mqtt()
    -- registering a timer
    tmr.register(MAINTIMER_ID, MAINTIMER_INTERVAL_MS, tmr.ALARM_AUTO, send_moisture_mqtt)
    tmr.start(MAINTIMER_ID)
end

function register_main_timer()

-- sending once the moisture wnen devices initialized

send_moisture_mqtt()

-- registering a timer

tmr.register(MAINTIMER_ID, MAINTIMER_INTERVAL_MS, tmr.ALARM_AUTO, send_moisture_mqtt)

tmr.start(MAINTIMER_ID)

end

And at last, we read the analogue input on NodeMCU to which a moisture sensor is attached. The MQTT json message is published to a defined topic with QoS = 1.

function send_moisture_mqtt()
    moisture = adc.read(0)
    r = mqtt_client:publish(MQTT_TOPIC, string.format("{\"moisture\": %d}", moisture), 1, 1)
end

function send_moisture_mqtt()

moisture = adc.read(0)

r = mqtt_client:publish(MQTT_TOPIC, string.format("{\"moisture\": %d}", moisture), 1, 1)

end

Referenced articles and documentation:
NEWBIE BUILDS A SOIL MOISTURE SENSOR ON NODEMCU (ESP8266)
Official NodeMCU documentation on MQTT Module
Official NodeMCU documentation on Wifi Module
Official NodeMCU documentation on Timer Module
Lua – Strings Tutorial

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Publishing MQTT messages from a NodeMCU – Soil Moisture Sensor

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