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Introduction

In this lesson, we will show how to use a MQTT client(MQTTBox here) to send a digit MQTT message to NodeMCU. NodeMCU will subscribe to corrsponding publish topic and display the subscription messages  on a 4-digit 7 segment LED device.

Preparation

Hardware:

Software:

Connection

NodeMCU 4 digital display
3.3V VCC
GND GND
D2 CLK
D3 DIO

Upload Sketch

Connect the NodeMCU to computer via USB cable,open this sketch by using Arduino IDE(Version1.6.4+):

Edit the code to fit your own WiFi and MQTT settings as following operations:

1)Hotspot Configration:

const char* ssid = "your_hotspot_ssid";

const char* password = "your_hotspot_password";

Find above code line,put your own ssid and password on there.

2)MQTT  Server  Address Setting

const char* mqtt_server = "broker.mqtt-dashboard.com";

You can use your own MQTT broker URL or IP address to set above mqtt_server value. You can also use some famous free MQTT server to test the project such as  "broker.mqtt-dashboard.com",  "iot.eclipse.org" etc.

3)MQTT Client Settings

If your MQTT broker require clientID,username and password authentication,you need to change

if (client.connect(clientId.c_str()))

to

if (client.connect(clientId,userName,passWord)) //put your clientId/userName/passWord here

If not,just keep them as default.

After do that,choose the coresponding board type and port type as below,then upload the sketch to the NodeMCU.

MQTT Client Settings

About how to config the MQTT clientr,check this link.

Topics Settings:

Running Result

Onece the upload done,if wifi hotspot name and password setting is ok and MQTT broker is connected, open the Serial Monitor,you will see following result:

The NodeMCU serial port will show the IP address and the connection satatus,then print the command from MQTT client.NOTE: When the number is between 0 and 191, it can be displayed normally.The initial state output value is 83.

Open the MQTTBox and publish different number(0~191) to the broker,

The 4 digital LED display will show as below :

The Serial Monitor output as below: