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Introduction

In this lesson, we will show how to check the potentiometer resistance value by NodeMCU, then send the resistance value to a MQTT broker via MQTT protocol,the MQTT client will subscribe to correspoding topic and get these values.

Preparation

Hardware:

Software:

Connection

Overhere,we use A0 as the analog input pin.

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.

  • Board:”NodeMCU 0.9(ESP-12 Module)”
  • CPU Frequency:”80MHz”
  • Flash Size:”4M (3M SPIFFS)”
  • Upload Speed:”115200″
  • Port: Choose your own Serial Port for your NodeMCU

MQTT Client Settings

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

Topics Settings:

  • Topic to subscribe: OsoyooData

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 resistance value.As you can see from the sketch,twist the knob of potentiometer, When the resistance value is more than 50, the serial output will be:

“0: The resistance value is: ** “

When the resistance value is less than 50, the serial output will be:

“1: The resistance value is:  **”

Open the MQTTBox and choose the corresponding subsucribe topic,click the Subscribe button, you will see the subscription information as below:

                                    

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