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Introduction

In this lesson, we will show how to use a MQTT client to remote control an active buzzer via MQTT protocol.

Preparation

Hardware:

(You can also add a series resistor to limit the buzzer current,it will decrease beep sound.)

Software:

Connection

Overhere,we use D2 as the output pin to control the buzzer.

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 client,check this link.

Topics Settings:

Running Result

Onece the upload done,if wifi hotspot ssid 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.

Next,open the MQTT client and publish "1" or "0" on the "OsoyooCommand" topic as below:

Then you will see the NodeMCU serial output. When you publish "1", the NodeMCU will subscribe this message and print "Command from MQTT broker is : [OsoyooCommand  Turn On Buzzer" on the serial monitor,the buzzer will beep; When you publish "0", the NodeMCU will subscribe this message and print "Command from MQTT broker is : [OsoyooCommand  Turn Off Buzzer",the buzzer will be turned off.