The following guide shows how to publish data to the AskSensors IoT platform using Arduino Ethernet shield and MQTT.

a) Prerequisites :

• Create an AskSensors account.
• Setup a new sensor.
• Get started using this step-by-step user guide.

b) Required Hardwares :

• Computer running Arduino software (version 1.8.7 or higher).
• Arduino Uno.
• Arduino Ethernet Shield
• USB micro cable to connect the ESP8266 board to the computer.
• RJ45 Ethernet Cable

c) Software:

• Install the MQTT PubSubClient Library for the Arduino IDE.
• Download this demo from the AskSensors Github page.

The provided code includes the libraries for both connecting to a Ethernet network and to publish data to AskSensors using MQTT.
You need to fill the following:

• • The Api Key In and username to set the MQTT Topic:publish/username/apiKeyIn
  • A fixed IP address.

const char* username = "................."; // my AskSensors username
const char* pubTopic = "publish/..../....."; // publish/username/apiKeyIn
IPAddress ip(..., ..., ..., ...); // IP address

d) Run the code:

• Connect your Arduino board to the computer via serial USB and upload the code using the Arduino IDE.
• Connect your Arduino Ethernet shield to the network through Ethernet cable
• Reset the board
• Return back to your sensor page on AskSensors, Click on’Show Graph’ and select the chart type (such as Line, Bar, Binary..) to visualize your sensor data stream in graph.
• Open a serial terminal. You can cross-check the AskSensors graph readings with the values being printed on your Arduino Terminal.

e) Source Code:

A basic source code is shown below. Please refer to the AskSensors Github page to get the latest version and updates.

/*
* MQTT and AskSensors IoT Platform
* Description: Arduino Ethernet publishes data to AskSensors using MQTT
* Author: https://asksensors.com, 2020
* github: https://github.com/asksensors
*/
#include <SPI.h>
#include <Ethernet.h>
#include <PubSubClient.h>
// TODO: AskSensors MQTT user config
const char* username = "................."; // my AskSensors username
const char* pubTopic = "publish/..../....."; // publish/username/apiKeyIn
const unsigned int writeInterval = 25000; // write interval (in ms)
// MQTT host config
const char* mqtt_server = "mqtt.asksensors.com";
unsigned int mqtt_port = 1883;
// ETHERNET config.
// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
// Set the static IP address to use if the DHCP fails to assign
IPAddress ip(..., ..., ..., ...); // TODO: Add the IP address
EthernetClient askClient;
PubSubClient client(askClient);
void setup() {
Serial.begin(115200);
Serial.println("*****************************************************");
Serial.println("********** Program Start : Arduino Ethernet publishes data to AskSensors over MQTT");
Serial.print("********** connecting to Ethernet : ");
// start the Ethernet connection:
if (Ethernet.begin(mac) == 0) {
Serial.println("Failed to configure Ethernet using DHCP");
// try to congifure using IP address instead of DHCP:
Ethernet.begin(mac, ip);
}
// give the Ethernet shield a second to initialize:
delay(1000);
client.setServer(mqtt_server, mqtt_port);
client.setCallback(callback);
}

void loop() {
if (!client.connected())
reconnect();
client.loop();
Serial.println("********** Publish MQTT data to ASKSENSORS");
char mqtt_payload[30] = "";
snprintf (mqtt_payload, 100, "m1=%ld&m2=%ld", random(10,100), random(10,100) );
Serial.print("Publish message: ");
Serial.println(mqtt_payload);
client.publish(pubTopic, mqtt_payload);
Serial.println("> MQTT data published");
Serial.println("********** End ");
Serial.println("*****************************************************");
delay(writeInterval);// delay
}
void callback(char* topic, byte* payload, unsigned int length) {
Serial.print("Message arrived [");
Serial.print(topic);
Serial.print("] ");
for (int i = 0; i < length; i++) {
Serial.print((char)payload[i]);
}
Serial.println();
}
void reconnect() {
// Loop until we're reconnected
while (!client.connected()) {
Serial.print("********** Attempting MQTT connection...");
// Attempt to connect
if (client.connect("ethClient",username, "")) {
Serial.println("-> MQTT client connected");
} else {
Serial.print("failed, rc=");
Serial.print(client.state());
Serial.println("-> try again in 5 seconds");
// Wait 5 seconds before retrying
delay(5000);
}
}
}