# Retrieve Last Data from Antares Server with MQTT Protocol In this project you will be directed to send simple data from the **Lynx-32 Development Board** to the **Antares IoT Platform** using WiFi connectivity with the MQTT protocol. ## Prerequisites The materials required follow the **General Prerequisites** on the previous page. If you have not prepared the requirements on that page, then you can visit the following page. {% content-ref url="/pages/Zpk3iTltrVZubNhHlGNm" %} [General Prerequisites ESP32 Wi-Fi](/en/code-and-library-examples/esp32-wi-fi/general-prerequisites-esp32-wi-fi.md) {% endcontent-ref %} The additional materials specific to this project are as follows. 1. Antares ESP HTTP Library. This documentation uses the **Antares ESP MQTT library version 1.0.** {% hint style="info" %} If you have not installed **Antares ESP MQTT** version 1.0, you can follow these steps. [Antares Wi-Fi MQTT](/en/getting-started/arduino-library-installation/antares-wi-fi-mqtt.md) {% endhint %} ## Follow These Steps ### 1. Run the Arduino IDE application ### 2. Opening Sample Programme {% hint style="info" %} You can open the programme code in the Arduino IDE via **File > Examples > Antares ESP MQTT > AntaresMQTTRetrieveLatestData.** {% endhint %} The following is the AntaresMQTTRetrieveLatestData example programme code ```arduino /* This is an example sketch to subscribe to MQTT data on ESP8266 via the Antares IoT Platform. MQTT server & port: platform.antares.id, port 1338 MQTT topic: /oneM2M/req/your-access-key/antares-cse/json The main function in this sketch is the callback function, which will be fired every time a new message is published to the topic. For more information, please visit https://antares.id/id/docs.html */ #include #define ACCESSKEY "YOUR-ACCESS-KEY" // Antares account access key #define WIFISSID "YOUR-WIFI-SSID" // Wi-Fi SSID to connect to #define PASSWORD "YOUR-WIFI-PASSWORD" // Wi-Fi password #define projectName "YOUR-APPLICATION-NAME" // Name of the application created in Antares #define deviceName "YOUR-DEVICE-NAME" // Name of the device created in Antares AntaresESPMQTT antares(ACCESSKEY); unsigned long previousMillis=0; unsigned long interval =5000; void callback(char topic[], byte payload[], unsigned int length) { /* Get the whole received data, including the topic, and parse the data according to the Antares data format. */ antares.get(topic, payload, length); Serial.println("New Message!"); // Print topic and payload Serial.println("Topic: " + antares.getTopic()); Serial.println("Payload: " + antares.getPayload()); // Print individual data } void setup() { Serial.begin(115200); antares.setDebug(true); antares.wifiConnection(WIFISSID, PASSWORD); antares.setMqttServer(); antares.setCallback(callback); } void loop() { /* Check if we're still connected to the MQTT broker/server. If disconnected, the device will try to reconnect. */ antares.checkMqttConnection(); while(millis()-previousMillis > interval) { previousMillis = millis(); antares.retrieveLastData(projectName,deviceName); } } ``` ### 3. Set MQTT Parameters in Programme Code Change the HTTP Protocol parameters in the following variables **\*ACCESSKEY, \*WIFISSID, \*PASSWORD, \*projectName,** and **\*deviceName**. Adjust to the parameters in the Antares console. ```arduino #define ACCESSKEY "YOUR-ACCESS-KEY" // Replace with your Antares account access key #define WIFISSID "YOUR-WIFI-SSID" // Replace with your Wi-Fi SSID #define PASSWORD "YOUR-WIFI-PASSWORD" // Replace with your Wi-Fi password #define projectName "YOUR-APPLICATION-NAME" // Replace with the Antares application name that was created #define deviceName "YOUR-DEVICE-NAME" // Replace with the Antares device name that was created ``` {% hint style="info" %} The **\*Access key** parameter is obtained from your Antares account page. {% endhint %}

Access Key Location on Antares Account Page

{% hint style="info" %} The **WIFISSID** parameter is obtained from the **Wi-Fi/Hotspot** name that will be used by the **Lynx-32 Development Board**. An example is shown below. {% endhint %}

{% hint style="info" %} The **\*PASSWORD** parameter is obtained from the **WiFi password** you are currently using. {% endhint %} {% hint style="info" %} The parameters **\*projectName** and **\*deviceName** are obtained from the **Application Name** and **Device Name** that have been created in the Antares account. {% endhint %}

### 4. Compile and Upload Program Connect the **Lynx-32** with your computer and make sure the **Communication Port** is read. {% hint style="info" %} On Windows operating systems the check can be done via **Device Manage**r. If your **Lynx-32** is read then the **USB-Serial CH340** appears with the port adjusting the port availability (in this case it reads **COM4**). {% endhint %}

Set up the **ESP32** board by clicking **Tools > Board > esp32** in the Arduino IDE, then make sure the **ESP32 Dev Module** is used. Select the port according to the communication port that is read (in this case COM4). The result will look like the following image.

Display of Board Specifications and Ports Used

After all the setup is complete, upload the programme by pressing the arrow icon as shown below. Wait for the compile and upload process to finish

Compile Icon for Tick and Upload Icon for Arrow

{% hint style="info" %} **The Tick icon** on the Arduino IDE is just the verify process. Usually used to **Compile** the programme to find out whether there are errors or not. \ **The Arrow icon** on the Arduino IDE is the verify and upload process. Usually used to **Compile** the programme as well as Flash the programme to the target board. {% endhint %} If the programme upload is successful, it will look like the following image.

Upload Successful Programme Output Display

After uploading the programme, you can view the **serial monitor** to debug the programme. The **serial monitor** icon is shown in the following image.

Set the **serial baud rate** to 115200 and select BothNL & CR. The result will look like the following image.

{% hint style="danger" %} Make sure the **serial baud rate** matches the value defined in the programme code. If the **serial baud rate** is not the same between the **programme code** and the **serial monitor**, the ASCII characters will not be read properly. {% endhint %} ### 5. Check Data in Antares After uploading the programme successfully, then open the Antares device page and see if the data taken matches the data in the Antares Console.

{% hint style="info" %} The data sent from the **Lynx-32 Development Board** with the MQTT protocol is in the form of temperature, humidity, wind\_speed, rain\_level, and location variables containing latitude and longitude. {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.antares.id/en/code-and-library-examples/esp32-wi-fi/esp32-wi-fi-mqtt-protocol/retrieve-last-data-from-antares-server-with-mqtt-protocol.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.