ESP8266 ESP201 : Blink LED remotely via Adafruit MQTT

After learning to send temperature data from ESP8266 module to a server (Adafruit MQTT), it was time to learn to send data from Adafruit MQTT to ESP8266 module.
In order to create a Toggle button in Adafruit IO which trigger the LED on ESP8266 module, we need to have Adafruit account; https://io.adafruit.com

After login to Adafruit IO :-
- Create a new dashboard. Enter project name.
- Choose Toggle option.
- Then, follow the steps of the setup wizard.

The Toggle button in Adafruit IO looks like on this picture :-

For wiring schematic , see below picture. It includes wiring to upload sketch or code to ESP8266 module :-

The code can be found here  https://github.com/adafruit/Adafruit_MQTT_Library/blob/master/examples/mqtt_esp8266/mqtt_esp8266.ino but it need to be modified because we only use a LED and it does not have code that trigger the LED.

Here is the modified code :-

	#include <ESP8266WiFi.h>
	#include "Adafruit_MQTT.h"
	#include "Adafruit_MQTT_Client.h"
	/************************* WiFi Access Point *********************************/
	#define WLAN_SSID "your-ssid"
	#define WLAN_PASS "your-password"
	/************************* Adafruit.io Setup *********************************/
	#define AIO_SERVER "io.adafruit.com"
	#define AIO_SERVERPORT 1883 // use 8883 for SSL
	#define AIO_USERNAME "...your-username..." //Put your Adafruit userid here
	#define AIO_KEY "...your-key...." // Put your Adafruit key here
	/************ Global State (you don't need to change this!) ******************/
	// Create an ESP8266 WiFiClient class to connect to the MQTT server.
	WiFiClient client;
	// or... use WiFiFlientSecure for SSL
	//WiFiClientSecure client;
	// Setup the MQTT client class by passing in the WiFi client and MQTT server and login details.
	Adafruit_MQTT_Client mqtt(&client, AIO_SERVER, AIO_SERVERPORT, AIO_USERNAME, AIO_KEY);
	/***************** LED setup ************************************/
	int ledPin = 2; // GPIO2 of ESP8266
	/****************************** Feeds ***************************************/
	// Setup a feed called 'photocell' for publishing.
	// Notice MQTT paths for AIO follow the form: <username>/feeds/<feedname>
	//Adafruit_MQTT_Publish photocell = Adafruit_MQTT_Publish(&mqtt, AIO_USERNAME "/feeds/photocell"); //Comment out because we don't use photocell.
	// Setup a feed called 'onoff' for subscribing to changes.
	Adafruit_MQTT_Subscribe onoffbutton = Adafruit_MQTT_Subscribe(&mqtt, AIO_USERNAME "/feeds/onoff");
	/*************************** Sketch Code ************************************/
	// Bug workaround for Arduino 1.6.6, it seems to need a function declaration
	// for some reason (only affects ESP8266, likely an arduino-builder bug).
	void MQTT_connect();
	void setup() {
	Serial.begin(115200);
	delay(10);
	//Led setup
	pinMode(ledPin, OUTPUT);
	digitalWrite(ledPin, LOW);
	Serial.println(F("Adafruit MQTT demo"));
	// Connect to WiFi access point.
	Serial.println(); Serial.println();
	Serial.print("Connecting to ");
	Serial.println(WLAN_SSID);
	WiFi.begin(WLAN_SSID, WLAN_PASS);
	while (WiFi.status() != WL_CONNECTED) {
	delay(500);
	Serial.print(".");
	}
	Serial.println();
	Serial.println("WiFi connected");
	Serial.println("IP address: "); Serial.println(WiFi.localIP());
	// Setup MQTT subscription for onoff feed.
	mqtt.subscribe(&onoffbutton);
	}
	uint32_t x=0;
	void loop() {
	// Ensure the connection to the MQTT server is alive (this will make the first
	// connection and automatically reconnect when disconnected). See the MQTT_connect
	// function definition further below.
	MQTT_connect();
	// this is our 'wait for incoming subscription packets' busy subloop
	// try to spend your time here
	Adafruit_MQTT_Subscribe *subscription;
	while ((subscription = mqtt.readSubscription(5000))) {
	if (subscription == &onoffbutton) {
	Serial.print("Got: ");
	Serial.println((char *)onoffbutton.lastread);
	if (strcmp((char *)onoffbutton.lastread, "ON") == 0) {
	digitalWrite(ledPin, HIGH);
	}
	if (strcmp((char *)onoffbutton.lastread, "OFF") == 0) {
	digitalWrite(ledPin, LOW);
	}
	}
	}
	// Now we can publish stuff!
	/* Comment out because we don't use photocell in this project.
	Serial.print(F("\nSending photocell val "));
	Serial.print(x);
	Serial.print("...");
	if (! photocell.publish(x++)) {
	Serial.println(F("Failed"));
	} else {
	Serial.println(F("OK!"));
	}
	*/
	// ping the server to keep the mqtt connection alive
	// NOT required if you are publishing once every KEEPALIVE seconds
	/*
	if(! mqtt.ping()) {
	mqtt.disconnect();
	}
	*/
	}
	// Function to connect and reconnect as necessary to the MQTT server.
	// Should be called in the loop function and it will take care if connecting.
	void MQTT_connect() {
	int8_t ret;
	// Stop if already connected.
	if (mqtt.connected()) {
	return;
	}
	Serial.print("Connecting to MQTT... ");
	uint8_t retries = 3;
	while ((ret = mqtt.connect()) != 0) { // connect will return 0 for connected
	Serial.println(mqtt.connectErrorString(ret));
	Serial.println("Retrying MQTT connection in 5 seconds...");
	mqtt.disconnect();
	delay(5000); // wait 5 seconds
	retries--;
	if (retries == 0) {
	// basically die and wait for WDT to reset me
	while (1);
	}
	}
	Serial.println("MQTT Connected!");
	}

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